--- /dev/null
+From: Roland McGrath <roland@redhat.com>
+Date: Mon Aug 25 17:22:07 2008 -0700
+Subject: utrace core
+References: FATE#304321
+Patch-mainline: no
+
+This adds the utrace facility, a new modular interface in the kernel for
+implementing user thread tracing and debugging. This fits on top of the
+tracehook_* layer, so the new code is well-isolated.
+
+The new interface is in <linux/utrace.h> and the DocBook utrace book
+describes it. It allows for multiple separate tracing engines to work in
+parallel without interfering with each other. Higher-level tracing
+facilities can be implemented as loadable kernel modules using this layer.
+
+The new facility is made optional under CONFIG_UTRACE.
+When this is not enabled, no new code is added.
+It can only be enabled on machines that have all the
+prerequisites and select CONFIG_HAVE_ARCH_TRACEHOOK.
+
+In this initial version, utrace and ptrace do not play well together.
+If both utrace and ptrace are attached to the same thread, they can
+confuse each other about the stopping and resuming of that thread.
+The old ptrace code is unchanged and nothing using ptrace should be
+affected by this patch as long as utrace is not used at the same time.
+A later patch will make them cooperate properly.
+
+Signed-off-by: Roland McGrath <roland@redhat.com>
+Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
+
+---
+ Documentation/DocBook/Makefile | 2
+ Documentation/DocBook/utrace.tmpl | 566 ++++++++
+ fs/proc/array.c | 3
+ include/linux/sched.h | 5
+ include/linux/tracehook.h | 71 +
+ include/linux/utrace.h | 711 ++++++++++
+ init/Kconfig | 10
+ kernel/Makefile | 1
+ kernel/utrace.c | 2495 ++++++++++++++++++++++++++++++++++++++
+ 9 files changed, 3862 insertions(+), 2 deletions(-)
+
+--- a/Documentation/DocBook/Makefile
++++ b/Documentation/DocBook/Makefile
+@@ -7,7 +7,7 @@
+ # list of DOCBOOKS.
+
+ DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \
+- kernel-hacking.xml kernel-locking.xml deviceiobook.xml \
++ kernel-hacking.xml kernel-locking.xml deviceiobook.xml utrace.xml \
+ procfs-guide.xml writing_usb_driver.xml networking.xml \
+ kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
+ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
+--- /dev/null
++++ b/Documentation/DocBook/utrace.tmpl
+@@ -0,0 +1,566 @@
++<?xml version="1.0" encoding="UTF-8"?>
++<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
++"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
++
++<book id="utrace">
++ <bookinfo>
++ <title>The utrace User Debugging Infrastructure</title>
++ </bookinfo>
++
++ <toc></toc>
++
++ <chapter id="concepts"><title>utrace concepts</title>
++
++ <sect1 id="intro"><title>Introduction</title>
++
++ <para>
++ <application>utrace</application> is infrastructure code for tracing
++ and controlling user threads. This is the foundation for writing
++ tracing engines, which can be loadable kernel modules.
++ </para>
++
++ <para>
++ The basic actors in <application>utrace</application> are the thread
++ and the tracing engine. A tracing engine is some body of code that
++ calls into the <filename><linux/utrace.h></filename>
++ interfaces, represented by a <structname>struct
++ utrace_engine_ops</structname>. (Usually it's a kernel module,
++ though the legacy <function>ptrace</function> support is a tracing
++ engine that is not in a kernel module.) The interface operates on
++ individual threads (<structname>struct task_struct</structname>).
++ If an engine wants to treat several threads as a group, that is up
++ to its higher-level code.
++ </para>
++
++ <para>
++ Tracing begins by attaching an engine to a thread, using
++ <function>utrace_attach_task</function> or
++ <function>utrace_attach_pid</function>. If successful, it returns a
++ pointer that is the handle used in all other calls.
++ </para>
++
++ </sect1>
++
++ <sect1 id="callbacks"><title>Events and Callbacks</title>
++
++ <para>
++ An attached engine does nothing by default. An engine makes something
++ happen by requesting callbacks via <function>utrace_set_events</function>
++ and poking the thread with <function>utrace_control</function>.
++ The synchronization issues related to these two calls
++ are discussed further below in <xref linkend="teardown"/>.
++ </para>
++
++ <para>
++ Events are specified using the macro
++ <constant>UTRACE_EVENT(<replaceable>type</replaceable>)</constant>.
++ Each event type is associated with a callback in <structname>struct
++ utrace_engine_ops</structname>. A tracing engine can leave unused
++ callbacks <constant>NULL</constant>. The only callbacks required
++ are those used by the event flags it sets.
++ </para>
++
++ <para>
++ Many engines can be attached to each thread. When a thread has an
++ event, each engine gets a callback if it has set the event flag for
++ that event type. Engines are called in the order they attached.
++ </para>
++
++ <para>
++ Event reporting callbacks have details particular to the event type,
++ but are all called in similar environments and have the same
++ constraints. Callbacks are made from safe points, where no locks
++ are held, no special resources are pinned (usually), and the
++ user-mode state of the thread is accessible. So, callback code has
++ a pretty free hand. But to be a good citizen, callback code should
++ never block for long periods. It is fine to block in
++ <function>kmalloc</function> and the like, but never wait for i/o or
++ for user mode to do something. If you need the thread to wait, use
++ <constant>UTRACE_STOP</constant> and return from the callback
++ quickly. When your i/o finishes or whatever, you can use
++ <function>utrace_control</function> to resume the thread.
++ </para>
++
++ </sect1>
++
++ <sect1 id="safely"><title>Stopping Safely</title>
++
++ <sect2 id="well-behaved"><title>Writing well-behaved callbacks</title>
++
++ <para>
++ Well-behaved callbacks are important to maintain two essential
++ properties of the interface. The first of these is that unrelated
++ tracing engines should not interfere with each other. If your engine's
++ event callback does not return quickly, then another engine won't get
++ the event notification in a timely manner. The second important
++ property is that tracing should be as noninvasive as possible to the
++ normal operation of the system overall and of the traced thread in
++ particular. That is, attached tracing engines should not perturb a
++ thread's behavior, except to the extent that changing its user-visible
++ state is explicitly what you want to do. (Obviously some perturbation
++ is unavoidable, primarily timing changes, ranging from small delays due
++ to the overhead of tracing, to arbitrary pauses in user code execution
++ when a user stops a thread with a debugger for examination.) Even when
++ you explicitly want the perturbation of making the traced thread block,
++ just blocking directly in your callback has more unwanted effects. For
++ example, the <constant>CLONE</constant> event callbacks are called when
++ the new child thread has been created but not yet started running; the
++ child can never be scheduled until the <constant>CLONE</constant>
++ tracing callbacks return. (This allows engines tracing the parent to
++ attach to the child.) If a <constant>CLONE</constant> event callback
++ blocks the parent thread, it also prevents the child thread from
++ running (even to process a <constant>SIGKILL</constant>). If what you
++ want is to make both the parent and child block, then use
++ <function>utrace_attach_task</function> on the child and then use
++ <constant>UTRACE_STOP</constant> on both threads. A more crucial
++ problem with blocking in callbacks is that it can prevent
++ <constant>SIGKILL</constant> from working. A thread that is blocking
++ due to <constant>UTRACE_STOP</constant> will still wake up and die
++ immediately when sent a <constant>SIGKILL</constant>, as all threads
++ should. Relying on the <application>utrace</application>
++ infrastructure rather than on private synchronization calls in event
++ callbacks is an important way to help keep tracing robustly
++ noninvasive.
++ </para>
++
++ </sect2>
++
++ <sect2 id="UTRACE_STOP"><title>Using <constant>UTRACE_STOP</constant></title>
++
++ <para>
++ To control another thread and access its state, it must be stopped
++ with <constant>UTRACE_STOP</constant>. This means that it is
++ stopped and won't start running again while we access it. When a
++ thread is not already stopped, <function>utrace_control</function>
++ returns <constant>-EINPROGRESS</constant> and an engine must wait
++ for an event callback when the thread is ready to stop. The thread
++ may be running on another CPU or may be blocked. When it is ready
++ to be examined, it will make callbacks to engines that set the
++ <constant>UTRACE_EVENT(QUIESCE)</constant> event bit. To wake up an
++ interruptible wait, use <constant>UTRACE_INTERRUPT</constant>.
++ </para>
++
++ <para>
++ As long as some engine has used <constant>UTRACE_STOP</constant> and
++ not called <function>utrace_control</function> to resume the thread,
++ then the thread will remain stopped. <constant>SIGKILL</constant>
++ will wake it up, but it will not run user code. When the stop is
++ cleared with <function>utrace_control</function> or a callback
++ return value, the thread starts running again.
++ (See also <xref linkend="teardown"/>.)
++ </para>
++
++ </sect2>
++
++ </sect1>
++
++ <sect1 id="teardown"><title>Tear-down Races</title>
++
++ <sect2 id="SIGKILL"><title>Primacy of <constant>SIGKILL</constant></title>
++ <para>
++ Ordinarily synchronization issues for tracing engines are kept fairly
++ straightforward by using <constant>UTRACE_STOP</constant>. You ask a
++ thread to stop, and then once it makes the
++ <function>report_quiesce</function> callback it cannot do anything else
++ that would result in another callback, until you let it with a
++ <function>utrace_control</function> call. This simple arrangement
++ avoids complex and error-prone code in each one of a tracing engine's
++ event callbacks to keep them serialized with the engine's other
++ operations done on that thread from another thread of control.
++ However, giving tracing engines complete power to keep a traced thread
++ stuck in place runs afoul of a more important kind of simplicity that
++ the kernel overall guarantees: nothing can prevent or delay
++ <constant>SIGKILL</constant> from making a thread die and release its
++ resources. To preserve this important property of
++ <constant>SIGKILL</constant>, it as a special case can break
++ <constant>UTRACE_STOP</constant> like nothing else normally can. This
++ includes both explicit <constant>SIGKILL</constant> signals and the
++ implicit <constant>SIGKILL</constant> sent to each other thread in the
++ same thread group by a thread doing an exec, or processing a fatal
++ signal, or making an <function>exit_group</function> system call. A
++ tracing engine can prevent a thread from beginning the exit or exec or
++ dying by signal (other than <constant>SIGKILL</constant>) if it is
++ attached to that thread, but once the operation begins, no tracing
++ engine can prevent or delay all other threads in the same thread group
++ dying.
++ </para>
++ </sect2>
++
++ <sect2 id="reap"><title>Final callbacks</title>
++ <para>
++ The <function>report_reap</function> callback is always the final event
++ in the life cycle of a traced thread. Tracing engines can use this as
++ the trigger to clean up their own data structures. The
++ <function>report_death</function> callback is always the penultimate
++ event a tracing engine might see; it's seen unless the thread was
++ already in the midst of dying when the engine attached. Many tracing
++ engines will have no interest in when a parent reaps a dead process,
++ and nothing they want to do with a zombie thread once it dies; for
++ them, the <function>report_death</function> callback is the natural
++ place to clean up data structures and detach. To facilitate writing
++ such engines robustly, given the asynchrony of
++ <constant>SIGKILL</constant>, and without error-prone manual
++ implementation of synchronization schemes, the
++ <application>utrace</application> infrastructure provides some special
++ guarantees about the <function>report_death</function> and
++ <function>report_reap</function> callbacks. It still takes some care
++ to be sure your tracing engine is robust to tear-down races, but these
++ rules make it reasonably straightforward and concise to handle a lot of
++ corner cases correctly.
++ </para>
++ </sect2>
++
++ <sect2 id="refcount"><title>Engine and task pointers</title>
++ <para>
++ The first sort of guarantee concerns the core data structures
++ themselves. <structname>struct utrace_attached_engine</structname> is
++ a reference-counted data structure. While you hold a reference, an
++ engine pointer will always stay valid so that you can safely pass it to
++ any <application>utrace</application> call. Each call to
++ <function>utrace_attach_task</function> or
++ <function>utrace_attach_pid</function> returns an engine pointer with a
++ reference belonging to the caller. You own that reference until you
++ drop it using <function>utrace_engine_put</function>. There is an
++ implicit reference on the engine while it is attached. So if you drop
++ your only reference, and then use
++ <function>utrace_attach_task</function> without
++ <constant>UTRACE_ATTACH_CREATE</constant> to look up that same engine,
++ you will get the same pointer with a new reference to replace the one
++ you dropped, just like calling <function>utrace_engine_get</function>.
++ When an engine has been detached, either explicitly with
++ <constant>UTRACE_DETACH</constant> or implicitly after
++ <function>report_reap</function>, then any references you hold are all
++ that keep the old engine pointer alive.
++ </para>
++
++ <para>
++ There is nothing a kernel module can do to keep a <structname>struct
++ task_struct</structname> alive outside of
++ <function>rcu_read_lock</function>. When the task dies and is reaped
++ by its parent (or itself), that structure can be freed so that any
++ dangling pointers you have stored become invalid.
++ <application>utrace</application> will not prevent this, but it can
++ help you detect it safely. By definition, a task that has been reaped
++ has had all its engines detached. All
++ <application>utrace</application> calls can be safely called on a
++ detached engine if the caller holds a reference on that engine pointer,
++ even if the task pointer passed in the call is invalid. All calls
++ return <constant>-ESRCH</constant> for a detached engine, which tells
++ you that the task pointer you passed could be invalid now. Since
++ <function>utrace_control</function> and
++ <function>utrace_set_events</function> do not block, you can call those
++ inside a <function>rcu_read_lock</function> section and be sure after
++ they don't return <constant>-ESRCH</constant> that the task pointer is
++ still valid until <function>rcu_read_unlock</function>. The
++ infrastructure never holds task references of its own. Though neither
++ <function>rcu_read_lock</function> nor any other lock is held while
++ making a callback, it's always guaranteed that the <structname>struct
++ task_struct</structname> and the <structname>struct
++ utrace_attached_engine</structname> passed as arguments remain valid
++ until the callback function returns.
++ </para>
++
++ <para>
++ The common means for safely holding task pointers that is available to
++ kernel modules is to use <structname>struct pid</structname>, which
++ permits <function>put_pid</function> from kernel modules. When using
++ that, the calls <function>utrace_attach_pid</function>,
++ <function>utrace_control_pid</function>,
++ <function>utrace_set_events_pid</function>, and
++ <function>utrace_barrier_pid</function> are available.
++ </para>
++ </sect2>
++
++ <sect2 id="reap-after-death">
++ <title>
++ Serialization of <constant>DEATH</constant> and <constant>REAP</constant>
++ </title>
++ <para>
++ The second guarantee is the serialization of
++ <constant>DEATH</constant> and <constant>REAP</constant> event
++ callbacks for a given thread. The actual reaping by the parent
++ (<function>release_task</function> call) can occur simultaneously
++ while the thread is still doing the final steps of dying, including
++ the <function>report_death</function> callback. If a tracing engine
++ has requested both <constant>DEATH</constant> and
++ <constant>REAP</constant> event reports, it's guaranteed that the
++ <function>report_reap</function> callback will not be made until
++ after the <function>report_death</function> callback has returned.
++ If the <function>report_death</function> callback itself detaches
++ from the thread, then the <function>report_reap</function> callback
++ will never be made. Thus it is safe for a
++ <function>report_death</function> callback to clean up data
++ structures and detach.
++ </para>
++ </sect2>
++
++ <sect2 id="interlock"><title>Interlock with final callbacks</title>
++ <para>
++ The final sort of guarantee is that a tracing engine will know for sure
++ whether or not the <function>report_death</function> and/or
++ <function>report_reap</function> callbacks will be made for a certain
++ thread. These tear-down races are disambiguated by the error return
++ values of <function>utrace_set_events</function> and
++ <function>utrace_control</function>. Normally
++ <function>utrace_control</function> called with
++ <constant>UTRACE_DETACH</constant> returns zero, and this means that no
++ more callbacks will be made. If the thread is in the midst of dying,
++ it returns <constant>-EALREADY</constant> to indicate that the
++ <constant>report_death</constant> callback may already be in progress;
++ when you get this error, you know that any cleanup your
++ <function>report_death</function> callback does is about to happen or
++ has just happened--note that if the <function>report_death</function>
++ callback does not detach, the engine remains attached until the thread
++ gets reaped. If the thread is in the midst of being reaped,
++ <function>utrace_control</function> returns <constant>-ESRCH</constant>
++ to indicate that the <function>report_reap</function> callback may
++ already be in progress; this means the engine is implicitly detached
++ when the callback completes. This makes it possible for a tracing
++ engine that has decided asynchronously to detach from a thread to
++ safely clean up its data structures, knowing that no
++ <function>report_death</function> or <function>report_reap</function>
++ callback will try to do the same. <constant>utrace_detach</constant>
++ returns <constant>-ESRCH</constant> when the <structname>struct
++ utrace_attached_engine</structname> has already been detached, but is
++ still a valid pointer because of its reference count. A tracing engine
++ can use this to safely synchronize its own independent multiple threads
++ of control with each other and with its event callbacks that detach.
++ </para>
++
++ <para>
++ In the same vein, <function>utrace_set_events</function> normally
++ returns zero; if the target thread was stopped before the call, then
++ after a successful call, no event callbacks not requested in the new
++ flags will be made. It fails with <constant>-EALREADY</constant> if
++ you try to clear <constant>UTRACE_EVENT(DEATH)</constant> when the
++ <function>report_death</function> callback may already have begun, if
++ you try to clear <constant>UTRACE_EVENT(REAP)</constant> when the
++ <function>report_reap</function> callback may already have begun, or if
++ you try to newly set <constant>UTRACE_EVENT(DEATH)</constant> or
++ <constant>UTRACE_EVENT(QUIESCE)</constant> when the target is already
++ dead or dying. Like <function>utrace_control</function>, it returns
++ <constant>-ESRCH</constant> when the thread has already been detached
++ (including forcible detach on reaping). This lets the tracing engine
++ know for sure which event callbacks it will or won't see after
++ <function>utrace_set_events</function> has returned. By checking for
++ errors, it can know whether to clean up its data structures immediately
++ or to let its callbacks do the work.
++ </para>
++ </sect2>
++
++ <sect2 id="barrier"><title>Using <function>utrace_barrier</function></title>
++ <para>
++ When a thread is safely stopped, calling
++ <function>utrace_control</function> with <constant>UTRACE_DETACH</constant>
++ or calling <function>utrace_set_events</function> to disable some events
++ ensures synchronously that your engine won't get any more of the callbacks
++ that have been disabled (none at all when detaching). But these can also
++ be used while the thread is not stopped, when it might be simultaneously
++ making a callback to your engine. For this situation, these calls return
++ <constant>-EINPROGRESS</constant> when it's possible a callback is in
++ progress. If you are not prepared to have your old callbacks still run,
++ then you can synchronize to be sure all the old callbacks are finished,
++ using <function>utrace_barrier</function>. This is necessary if the
++ kernel module containing your callback code is going to be unloaded.
++ </para>
++ <para>
++ After using <constant>UTRACE_DETACH</constant> once, further calls to
++ <function>utrace_control</function> with the same engine pointer will
++ return <constant>-ESRCH</constant>. In contrast, after getting
++ <constant>-EINPROGRESS</constant> from
++ <function>utrace_set_events</function>, you can call
++ <function>utrace_set_events</function> again later and if it returns zero
++ then know the old callbacks have finished.
++ </para>
++ <para>
++ Unlike all other calls, <function>utrace_barrier</function> (and
++ <function>utrace_barrier_pid</function>) will accept any engine pointer you
++ hold a reference on, even if <constant>UTRACE_DETACH</constant> has already
++ been used. After any <function>utrace_control</function> or
++ <function>utrace_set_events</function> call (these do not block), you can
++ call <function>utrace_barrier</function> to block until callbacks have
++ finished. This returns <constant>-ESRCH</constant> only if the engine is
++ completely detached (finished all callbacks). Otherwise returns it waits
++ until the thread is definitely not in the midst of a callback to this
++ engine and then returns zero, but can return
++ <constant>-ERESTARTSYS</constant> if its wait is interrupted.
++ </para>
++ </sect2>
++
++</sect1>
++
++</chapter>
++
++<chapter id="core"><title>utrace core API</title>
++
++<para>
++ The utrace API is declared in <filename><linux/utrace.h></filename>.
++</para>
++
++!Iinclude/linux/utrace.h
++!Ekernel/utrace.c
++
++</chapter>
++
++<chapter id="machine"><title>Machine State</title>
++
++<para>
++ The <function>task_current_syscall</function> function can be used on any
++ valid <structname>struct task_struct</structname> at any time, and does
++ not even require that <function>utrace_attach_task</function> was used at all.
++</para>
++
++<para>
++ The other ways to access the registers and other machine-dependent state of
++ a task can only be used on a task that is at a known safe point. The safe
++ points are all the places where <function>utrace_set_events</function> can
++ request callbacks (except for the <constant>DEATH</constant> and
++ <constant>REAP</constant> events). So at any event callback, it is safe to
++ examine <varname>current</varname>.
++</para>
++
++<para>
++ One task can examine another only after a callback in the target task that
++ returns <constant>UTRACE_STOP</constant> so that task will not return to user
++ mode after the safe point. This guarantees that the task will not resume
++ until the same engine uses <function>utrace_control</function>, unless the
++ task dies suddenly. To examine safely, one must use a pair of calls to
++ <function>utrace_prepare_examine</function> and
++ <function>utrace_finish_examine</function> surrounding the calls to
++ <structname>struct user_regset</structname> functions or direct examination
++ of task data structures. <function>utrace_prepare_examine</function> returns
++ an error if the task is not properly stopped and not dead. After a
++ successful examination, the paired <function>utrace_finish_examine</function>
++ call returns an error if the task ever woke up during the examination. If
++ so, any data gathered may be scrambled and should be discarded. This means
++ there was a spurious wake-up (which should not happen), or a sudden death.
++</para>
++
++<sect1 id="regset"><title><structname>struct user_regset</structname></title>
++
++<para>
++ The <structname>struct user_regset</structname> API
++ is declared in <filename><linux/regset.h></filename>.
++</para>
++
++!Finclude/linux/regset.h
++
++</sect1>
++
++<sect1 id="task_current_syscall">
++ <title><filename>System Call Information</filename></title>
++
++<para>
++ This function is declared in <filename><linux/ptrace.h></filename>.
++</para>
++
++!Elib/syscall.c
++
++</sect1>
++
++<sect1 id="syscall"><title><filename>System Call Tracing</filename></title>
++
++<para>
++ The arch API for system call information is declared in
++ <filename><asm/syscall.h></filename>.
++ Each of these calls can be used only at system call entry tracing,
++ or can be used only at system call exit and the subsequent safe points
++ before returning to user mode.
++ At system call entry tracing means either during a
++ <structfield>report_syscall_entry</structfield> callback,
++ or any time after that callback has returned <constant>UTRACE_STOP</constant>.
++</para>
++
++!Finclude/asm-generic/syscall.h
++
++</sect1>
++
++</chapter>
++
++<chapter id="internals"><title>Kernel Internals</title>
++
++<para>
++ This chapter covers the interface to the tracing infrastructure
++ from the core of the kernel and the architecture-specific code.
++ This is for maintainers of the kernel and arch code, and not relevant
++ to using the tracing facilities described in preceding chapters.
++</para>
++
++<sect1 id="tracehook"><title>Core Calls In</title>
++
++<para>
++ These calls are declared in <filename><linux/tracehook.h></filename>.
++ The core kernel calls these functions at various important places.
++</para>
++
++!Finclude/linux/tracehook.h
++
++</sect1>
++
++<sect1 id="arch"><title>Architecture Calls Out</title>
++
++<para>
++ An arch that has done all these things sets
++ <constant>CONFIG_HAVE_ARCH_TRACEHOOK</constant>.
++ This is required to enable the <application>utrace</application> code.
++</para>
++
++<sect2 id="arch-ptrace"><title><filename><asm/ptrace.h></filename></title>
++
++<para>
++ An arch defines these in <filename><asm/ptrace.h></filename>
++ if it supports hardware single-step or block-step features.
++</para>
++
++!Finclude/linux/ptrace.h arch_has_single_step arch_has_block_step
++!Finclude/linux/ptrace.h user_enable_single_step user_enable_block_step
++!Finclude/linux/ptrace.h user_disable_single_step
++
++</sect2>
++
++<sect2 id="arch-syscall">
++ <title><filename><asm/syscall.h></filename></title>
++
++ <para>
++ An arch provides <filename><asm/syscall.h></filename> that
++ defines these as inlines, or declares them as exported functions.
++ These interfaces are described in <xref linkend="syscall"/>.
++ </para>
++
++</sect2>
++
++<sect2 id="arch-tracehook">
++ <title><filename><linux/tracehook.h></filename></title>
++
++ <para>
++ An arch must define <constant>TIF_NOTIFY_RESUME</constant>
++ and <constant>TIF_SYSCALL_TRACE</constant>
++ in its <filename><asm/thread_info.h></filename>.
++ The arch code must call the following functions, all declared
++ in <filename><linux/tracehook.h></filename> and
++ described in <xref linkend="tracehook"/>:
++
++ <itemizedlist>
++ <listitem>
++ <para><function>tracehook_notify_resume</function></para>
++ </listitem>
++ <listitem>
++ <para><function>tracehook_report_syscall_entry</function></para>
++ </listitem>
++ <listitem>
++ <para><function>tracehook_report_syscall_exit</function></para>
++ </listitem>
++ <listitem>
++ <para><function>tracehook_signal_handler</function></para>
++ </listitem>
++ </itemizedlist>
++
++ </para>
++
++</sect2>
++
++</sect1>
++
++</chapter>
++
++</book>
+--- a/fs/proc/array.c
++++ b/fs/proc/array.c
+@@ -82,6 +82,7 @@
+ #include <linux/pid_namespace.h>
+ #include <linux/ptrace.h>
+ #include <linux/tracehook.h>
++#include <linux/utrace.h>
+
+ #include <asm/pgtable.h>
+ #include <asm/processor.h>
+@@ -191,6 +192,8 @@ static inline void task_state(struct seq
+ p->uid, p->euid, p->suid, p->fsuid,
+ p->gid, p->egid, p->sgid, p->fsgid);
+
++ task_utrace_proc_status(m, p);
++
+ task_lock(p);
+ if (p->files)
+ fdt = files_fdtable(p->files);
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -1202,6 +1202,11 @@ struct task_struct {
+ #endif
+ seccomp_t seccomp;
+
++#ifdef CONFIG_UTRACE
++ struct utrace *utrace;
++ unsigned long utrace_flags;
++#endif
++
+ /* Thread group tracking */
+ u32 parent_exec_id;
+ u32 self_exec_id;
+--- a/include/linux/tracehook.h
++++ b/include/linux/tracehook.h
+@@ -49,6 +49,7 @@
+ #include <linux/sched.h>
+ #include <linux/ptrace.h>
+ #include <linux/security.h>
++#include <linux/utrace.h>
+ struct linux_binprm;
+
+ /**
+@@ -63,6 +64,8 @@ struct linux_binprm;
+ */
+ static inline int tracehook_expect_breakpoints(struct task_struct *task)
+ {
++ if (unlikely(task_utrace_flags(task) & UTRACE_EVENT(SIGNAL_CORE)))
++ return 1;
+ return (task_ptrace(task) & PT_PTRACED) != 0;
+ }
+
+@@ -111,6 +114,9 @@ static inline void ptrace_report_syscall
+ static inline __must_check int tracehook_report_syscall_entry(
+ struct pt_regs *regs)
+ {
++ if ((task_utrace_flags(current) & UTRACE_EVENT(SYSCALL_ENTRY)) &&
++ utrace_report_syscall_entry(regs))
++ return 1;
+ ptrace_report_syscall(regs);
+ return 0;
+ }
+@@ -134,6 +140,8 @@ static inline __must_check int tracehook
+ */
+ static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
+ {
++ if (task_utrace_flags(current) & UTRACE_EVENT(SYSCALL_EXIT))
++ utrace_report_syscall_exit(regs);
+ ptrace_report_syscall(regs);
+ }
+
+@@ -155,6 +163,8 @@ static inline int tracehook_unsafe_exec(
+ else
+ unsafe |= LSM_UNSAFE_PTRACE;
+ }
++ if (unlikely(task_utrace_flags(task)))
++ unsafe |= utrace_unsafe_exec(task);
+ return unsafe;
+ }
+
+@@ -173,6 +183,8 @@ static inline struct task_struct *traceh
+ {
+ if (task_ptrace(tsk) & PT_PTRACED)
+ return rcu_dereference(tsk->parent);
++ if (unlikely(task_utrace_flags(tsk)))
++ return utrace_tracer_task(tsk);
+ return NULL;
+ }
+
+@@ -194,6 +206,8 @@ static inline void tracehook_report_exec
+ struct linux_binprm *bprm,
+ struct pt_regs *regs)
+ {
++ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(EXEC)))
++ utrace_report_exec(fmt, bprm, regs);
+ if (!ptrace_event(PT_TRACE_EXEC, PTRACE_EVENT_EXEC, 0) &&
+ unlikely(task_ptrace(current) & PT_PTRACED))
+ send_sig(SIGTRAP, current, 0);
+@@ -211,6 +225,8 @@ static inline void tracehook_report_exec
+ */
+ static inline void tracehook_report_exit(long *exit_code)
+ {
++ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(EXIT)))
++ utrace_report_exit(exit_code);
+ ptrace_event(PT_TRACE_EXIT, PTRACE_EVENT_EXIT, *exit_code);
+ }
+
+@@ -254,6 +270,7 @@ static inline int tracehook_prepare_clon
+ static inline void tracehook_finish_clone(struct task_struct *child,
+ unsigned long clone_flags, int trace)
+ {
++ utrace_init_task(child);
+ ptrace_init_task(child, (clone_flags & CLONE_PTRACE) || trace);
+ }
+
+@@ -280,6 +297,8 @@ static inline void tracehook_report_clon
+ unsigned long clone_flags,
+ pid_t pid, struct task_struct *child)
+ {
++ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(CLONE)))
++ utrace_report_clone(clone_flags, child);
+ if (unlikely(trace) || unlikely(clone_flags & CLONE_PTRACE)) {
+ /*
+ * The child starts up with an immediate SIGSTOP.
+@@ -345,6 +364,11 @@ static inline void tracehook_report_vfor
+ */
+ static inline void tracehook_prepare_release_task(struct task_struct *task)
+ {
++#ifdef CONFIG_UTRACE
++ smp_mb();
++ if (task_utrace_struct(task) != NULL)
++ utrace_release_task(task);
++#endif
+ }
+
+ /**
+@@ -358,7 +382,25 @@ static inline void tracehook_prepare_rel
+ */
+ static inline void tracehook_finish_release_task(struct task_struct *task)
+ {
++#ifdef CONFIG_UTRACE
++ int bad = 0;
++#endif
+ ptrace_release_task(task);
++#ifdef CONFIG_UTRACE
++ BUG_ON(task->exit_state != EXIT_DEAD);
++ if (unlikely(task_utrace_struct(task) != NULL)) {
++ /*
++ * In a race condition, utrace_attach() will temporarily set
++ * it, but then check @task->exit_state and clear it. It does
++ * all this under task_lock(), so we take the lock to check
++ * that there is really a bug and not just that known race.
++ */
++ task_lock(task);
++ bad = unlikely(task_utrace_struct(task) != NULL);
++ task_unlock(task);
++ }
++ BUG_ON(bad);
++#endif
+ }
+
+ /**
+@@ -380,6 +422,8 @@ static inline void tracehook_signal_hand
+ const struct k_sigaction *ka,
+ struct pt_regs *regs, int stepping)
+ {
++ if (task_utrace_flags(current))
++ utrace_signal_handler(current, stepping);
+ if (stepping)
+ ptrace_notify(SIGTRAP);
+ }
+@@ -400,6 +444,8 @@ static inline int tracehook_consider_ign
+ int sig,
+ void __user *handler)
+ {
++ if (unlikely(task_utrace_flags(task) & UTRACE_EVENT(SIGNAL_IGN)))
++ return 1;
+ return (task_ptrace(task) & PT_PTRACED) != 0;
+ }
+
+@@ -421,6 +467,9 @@ static inline int tracehook_consider_fat
+ int sig,
+ void __user *handler)
+ {
++ if (unlikely(task_utrace_flags(task) & (UTRACE_EVENT(SIGNAL_TERM) |
++ UTRACE_EVENT(SIGNAL_CORE))))
++ return 1;
+ return (task_ptrace(task) & PT_PTRACED) != 0;
+ }
+
+@@ -435,6 +484,8 @@ static inline int tracehook_consider_fat
+ */
+ static inline int tracehook_force_sigpending(void)
+ {
++ if (unlikely(task_utrace_flags(current)))
++ return utrace_interrupt_pending();
+ return 0;
+ }
+
+@@ -464,6 +515,8 @@ static inline int tracehook_get_signal(s
+ siginfo_t *info,
+ struct k_sigaction *return_ka)
+ {
++ if (unlikely(task_utrace_flags(task)))
++ return utrace_get_signal(task, regs, info, return_ka);
+ return 0;
+ }
+
+@@ -484,6 +537,8 @@ static inline int tracehook_get_signal(s
+ */
+ static inline int tracehook_notify_jctl(int notify, int why)
+ {
++ if (task_utrace_flags(current) & UTRACE_EVENT(JCTL))
++ utrace_report_jctl(notify, why);
+ return notify || (current->ptrace & PT_PTRACED);
+ }
+
+@@ -507,6 +562,10 @@ static inline int tracehook_notify_jctl(
+ static inline int tracehook_notify_death(struct task_struct *task,
+ void **death_cookie, int group_dead)
+ {
++#ifdef CONFIG_UTRACE
++ *death_cookie = task_utrace_struct(task);
++#endif
++
+ if (task->exit_signal == -1)
+ return task->ptrace ? SIGCHLD : DEATH_REAP;
+
+@@ -543,6 +602,12 @@ static inline void tracehook_report_deat
+ int signal, void *death_cookie,
+ int group_dead)
+ {
++#ifdef CONFIG_UTRACE
++ smp_mb();
++ if (task_utrace_flags(task) & (UTRACE_EVENT(DEATH) |
++ UTRACE_EVENT(QUIESCE)))
++ utrace_report_death(task, death_cookie, group_dead, signal);
++#endif
+ }
+
+ #ifdef TIF_NOTIFY_RESUME
+@@ -572,10 +637,14 @@ static inline void set_notify_resume(str
+ * asynchronously, this will be called again before we return to
+ * user mode.
+ *
+- * Called without locks.
++ * Called without locks. However, on some machines this may be
++ * called with interrupts disabled.
+ */
+ static inline void tracehook_notify_resume(struct pt_regs *regs)
+ {
++ struct task_struct *task = current;
++ if (task_utrace_flags(task))
++ utrace_resume(task, regs);
+ }
+ #endif /* TIF_NOTIFY_RESUME */
+
+--- /dev/null
++++ b/include/linux/utrace.h
+@@ -0,0 +1,711 @@
++/*
++ * utrace infrastructure interface for debugging user processes
++ *
++ * Copyright (C) 2006, 2007, 2008 Red Hat, Inc. All rights reserved.
++ *
++ * This copyrighted material is made available to anyone wishing to use,
++ * modify, copy, or redistribute it subject to the terms and conditions
++ * of the GNU General Public License v.2.
++ *
++ * Red Hat Author: Roland McGrath.
++ *
++ * This interface allows for notification of interesting events in a
++ * thread. It also mediates access to thread state such as registers.
++ * Multiple unrelated users can be associated with a single thread.
++ * We call each of these a tracing engine.
++ *
++ * A tracing engine starts by calling utrace_attach_task() or
++ * utrace_attach_pid() on the chosen thread, passing in a set of hooks
++ * (&struct utrace_engine_ops), and some associated data. This produces a
++ * &struct utrace_attached_engine, which is the handle used for all other
++ * operations. An attached engine has its ops vector, its data, and an
++ * event mask controlled by utrace_set_events().
++ *
++ * For each event bit that is set, that engine will get the
++ * appropriate ops->report_*() callback when the event occurs. The
++ * &struct utrace_engine_ops need not provide callbacks for an event
++ * unless the engine sets one of the associated event bits.
++ */
++
++#ifndef _LINUX_UTRACE_H
++#define _LINUX_UTRACE_H 1
++
++#include <linux/list.h>
++#include <linux/kref.h>
++#include <linux/signal.h>
++#include <linux/sched.h>
++
++struct linux_binprm;
++struct pt_regs;
++struct utrace;
++struct utrace_engine_ops;
++struct utrace_attached_engine;
++struct utrace_examiner;
++struct user_regset;
++struct user_regset_view;
++enum utrace_resume_action;
++
++/*
++ * Event bits passed to utrace_set_events().
++ * These appear in &struct task_struct.@utrace_flags
++ * and &struct utrace_attached_engine.@flags.
++ */
++enum utrace_events {
++ _UTRACE_EVENT_QUIESCE, /* Thread is available for examination. */
++ _UTRACE_EVENT_REAP, /* Zombie reaped, no more tracing possible. */
++ _UTRACE_EVENT_CLONE, /* Successful clone/fork/vfork just done. */
++ _UTRACE_EVENT_EXEC, /* Successful execve just completed. */
++ _UTRACE_EVENT_EXIT, /* Thread exit in progress. */
++ _UTRACE_EVENT_DEATH, /* Thread has died. */
++ _UTRACE_EVENT_SYSCALL_ENTRY, /* User entered kernel for system call. */
++ _UTRACE_EVENT_SYSCALL_EXIT, /* Returning to user after system call. */
++ _UTRACE_EVENT_SIGNAL, /* Signal delivery will run a user handler. */
++ _UTRACE_EVENT_SIGNAL_IGN, /* No-op signal to be delivered. */
++ _UTRACE_EVENT_SIGNAL_STOP, /* Signal delivery will suspend. */
++ _UTRACE_EVENT_SIGNAL_TERM, /* Signal delivery will terminate. */
++ _UTRACE_EVENT_SIGNAL_CORE, /* Signal delivery will dump core. */
++ _UTRACE_EVENT_JCTL, /* Job control stop or continue completed. */
++ _UTRACE_NEVENTS
++};
++#define UTRACE_EVENT(type) (1UL << _UTRACE_EVENT_##type)
++
++/*
++ * All the kinds of signal events.
++ * These all use the @report_signal() callback.
++ */
++#define UTRACE_EVENT_SIGNAL_ALL (UTRACE_EVENT(SIGNAL) \
++ | UTRACE_EVENT(SIGNAL_IGN) \
++ | UTRACE_EVENT(SIGNAL_STOP) \
++ | UTRACE_EVENT(SIGNAL_TERM) \
++ | UTRACE_EVENT(SIGNAL_CORE))
++/*
++ * Both kinds of syscall events; these call the @report_syscall_entry()
++ * and @report_syscall_exit() callbacks, respectively.
++ */
++#define UTRACE_EVENT_SYSCALL \
++ (UTRACE_EVENT(SYSCALL_ENTRY) | UTRACE_EVENT(SYSCALL_EXIT))
++
++/*
++ * Hooks in <linux/tracehook.h> call these entry points to the
++ * utrace dispatch. They are weak references here only so
++ * tracehook.h doesn't need to #ifndef CONFIG_UTRACE them to
++ * avoid external references in case of unoptimized compilation.
++ */
++void utrace_release_task(struct task_struct *)
++ __attribute__((weak));
++bool utrace_interrupt_pending(void)
++ __attribute__((weak));
++void utrace_resume(struct task_struct *, struct pt_regs *)
++ __attribute__((weak));
++int utrace_get_signal(struct task_struct *, struct pt_regs *,
++ siginfo_t *, struct k_sigaction *)
++ __attribute__((weak));
++void utrace_report_clone(unsigned long, struct task_struct *)
++ __attribute__((weak));
++void utrace_report_exit(long *exit_code)
++ __attribute__((weak));
++void utrace_report_death(struct task_struct *, struct utrace *, bool, int)
++ __attribute__((weak));
++void utrace_report_jctl(int notify, int type)
++ __attribute__((weak));
++void utrace_report_exec(struct linux_binfmt *, struct linux_binprm *,
++ struct pt_regs *regs)
++ __attribute__((weak));
++bool utrace_report_syscall_entry(struct pt_regs *)
++ __attribute__((weak));
++void utrace_report_syscall_exit(struct pt_regs *)
++ __attribute__((weak));
++struct task_struct *utrace_tracer_task(struct task_struct *)
++ __attribute__((weak));
++int utrace_unsafe_exec(struct task_struct *)
++ __attribute__((weak));
++void utrace_signal_handler(struct task_struct *, int)
++ __attribute__((weak));
++
++#ifndef CONFIG_UTRACE
++
++/*
++ * <linux/tracehook.h> uses these accessors to avoid #ifdef CONFIG_UTRACE.
++ */
++static inline unsigned long task_utrace_flags(struct task_struct *task)
++{
++ return 0;
++}
++static inline struct utrace *task_utrace_struct(struct task_struct *task)
++{
++ return NULL;
++}
++static inline void utrace_init_task(struct task_struct *child)
++{
++}
++
++static inline void task_utrace_proc_status(struct seq_file *m,
++ struct task_struct *p)
++{
++}
++
++#else /* CONFIG_UTRACE */
++
++static inline unsigned long task_utrace_flags(struct task_struct *task)
++{
++ return task->utrace_flags;
++}
++
++static inline struct utrace *task_utrace_struct(struct task_struct *task)
++{
++ return task->utrace;
++}
++
++static inline void utrace_init_task(struct task_struct *child)
++{
++ child->utrace_flags = 0;
++ child->utrace = NULL;
++}
++
++void task_utrace_proc_status(struct seq_file *m, struct task_struct *p);
++
++/*
++ * These are the exported entry points for tracing engines to use.
++ * See kernel/utrace.c for their kerneldoc comments with interface details.
++ */
++struct utrace_attached_engine *utrace_attach_task(
++ struct task_struct *, int, const struct utrace_engine_ops *, void *);
++struct utrace_attached_engine *utrace_attach_pid(
++ struct pid *, int, const struct utrace_engine_ops *, void *);
++int __must_check utrace_control(struct task_struct *,
++ struct utrace_attached_engine *,
++ enum utrace_resume_action);
++int __must_check utrace_set_events(struct task_struct *,
++ struct utrace_attached_engine *,
++ unsigned long eventmask);
++int __must_check utrace_barrier(struct task_struct *,
++ struct utrace_attached_engine *);
++int __must_check utrace_prepare_examine(struct task_struct *,
++ struct utrace_attached_engine *,
++ struct utrace_examiner *);
++int __must_check utrace_finish_examine(struct task_struct *,
++ struct utrace_attached_engine *,
++ struct utrace_examiner *);
++void __utrace_engine_release(struct kref *);
++
++/**
++ * enum utrace_resume_action - engine's choice of action for a traced task
++ * @UTRACE_STOP: Stay quiescent after callbacks.
++ * @UTRACE_REPORT: Make some callback soon.
++ * @UTRACE_INTERRUPT: Make @report_signal() callback soon.
++ * @UTRACE_SINGLESTEP: Resume in user mode for one instruction.
++ * @UTRACE_BLOCKSTEP: Resume in user mode until next branch.
++ * @UTRACE_RESUME: Resume normally in user mode.
++ * @UTRACE_DETACH: Detach my engine (implies %UTRACE_RESUME).
++ *
++ * See utrace_control() for detailed descriptions of each action. This is
++ * encoded in the @action argument and the return value for every callback
++ * with a &u32 return value.
++ *
++ * The order of these is important. When there is more than one engine,
++ * each supplies its choice and the smallest value prevails.
++ */
++enum utrace_resume_action {
++ UTRACE_STOP,
++ UTRACE_REPORT,
++ UTRACE_INTERRUPT,
++ UTRACE_SINGLESTEP,
++ UTRACE_BLOCKSTEP,
++ UTRACE_RESUME,
++ UTRACE_DETACH
++};
++#define UTRACE_RESUME_MASK 0x0f
++
++/**
++ * utrace_resume_action - &enum utrace_resume_action from callback action
++ * @action: &u32 callback @action argument or return value
++ *
++ * This extracts the &enum utrace_resume_action from @action,
++ * which is the @action argument to a &struct utrace_engine_ops
++ * callback or the return value from one.
++ */
++static inline enum utrace_resume_action utrace_resume_action(u32 action)
++{
++ return action & UTRACE_RESUME_MASK;
++}
++
++/**
++ * enum utrace_signal_action - disposition of signal
++ * @UTRACE_SIGNAL_DELIVER: Deliver according to sigaction.
++ * @UTRACE_SIGNAL_IGN: Ignore the signal.
++ * @UTRACE_SIGNAL_TERM: Terminate the process.
++ * @UTRACE_SIGNAL_CORE: Terminate with core dump.
++ * @UTRACE_SIGNAL_STOP: Deliver as absolute stop.
++ * @UTRACE_SIGNAL_TSTP: Deliver as job control stop.
++ * @UTRACE_SIGNAL_REPORT: Reporting before pending signals.
++ * @UTRACE_SIGNAL_HANDLER: Reporting after signal handler setup.
++ *
++ * This is encoded in the @action argument and the return value for
++ * a @report_signal() callback. It says what will happen to the
++ * signal described by the &siginfo_t parameter to the callback.
++ *
++ * The %UTRACE_SIGNAL_REPORT value is used in an @action argument when
++ * a tracing report is being made before dequeuing any pending signal.
++ * If this is immediately after a signal handler has been set up, then
++ * %UTRACE_SIGNAL_HANDLER is used instead. A @report_signal callback
++ * that uses %UTRACE_SIGNAL_DELIVER|%UTRACE_SINGLESTEP will ensure
++ * it sees a %UTRACE_SIGNAL_HANDLER report.
++ */
++enum utrace_signal_action {
++ UTRACE_SIGNAL_DELIVER = 0x00,
++ UTRACE_SIGNAL_IGN = 0x10,
++ UTRACE_SIGNAL_TERM = 0x20,
++ UTRACE_SIGNAL_CORE = 0x30,
++ UTRACE_SIGNAL_STOP = 0x40,
++ UTRACE_SIGNAL_TSTP = 0x50,
++ UTRACE_SIGNAL_REPORT = 0x60,
++ UTRACE_SIGNAL_HANDLER = 0x70
++};
++#define UTRACE_SIGNAL_MASK 0xf0
++#define UTRACE_SIGNAL_HOLD 0x100 /* Flag, push signal back on queue. */
++
++/**
++ * utrace_signal_action - &enum utrace_signal_action from callback action
++ * @action: @report_signal callback @action argument or return value
++ *
++ * This extracts the &enum utrace_signal_action from @action, which
++ * is the @action argument to a @report_signal callback or the
++ * return value from one.
++ */
++static inline enum utrace_signal_action utrace_signal_action(u32 action)
++{
++ return action & UTRACE_SIGNAL_MASK;
++}
++
++/**
++ * enum utrace_syscall_action - disposition of system call attempt
++ * @UTRACE_SYSCALL_RUN: Run the system call.
++ * @UTRACE_SYSCALL_ABORT: Don't run the system call.
++ *
++ * This is encoded in the @action argument and the return value for
++ * a @report_syscall_entry callback.
++ */
++enum utrace_syscall_action {
++ UTRACE_SYSCALL_RUN = 0x00,
++ UTRACE_SYSCALL_ABORT = 0x10
++};
++#define UTRACE_SYSCALL_MASK 0xf0
++
++/**
++ * utrace_syscall_action - &enum utrace_syscall_action from callback action
++ * @action: @report_syscall_entry callback @action or return value
++ *
++ * This extracts the &enum utrace_syscall_action from @action, which
++ * is the @action argument to a @report_syscall_entry callback or the
++ * return value from one.
++ */
++static inline enum utrace_syscall_action utrace_syscall_action(u32 action)
++{
++ return action & UTRACE_SYSCALL_MASK;
++}
++
++/*
++ * Flags for utrace_attach_task() and utrace_attach_pid().
++ */
++#define UTRACE_ATTACH_CREATE 0x0010 /* Attach a new engine. */
++#define UTRACE_ATTACH_EXCLUSIVE 0x0020 /* Refuse if existing match. */
++#define UTRACE_ATTACH_MATCH_OPS 0x0001 /* Match engines on ops. */
++#define UTRACE_ATTACH_MATCH_DATA 0x0002 /* Match engines on data. */
++#define UTRACE_ATTACH_MATCH_MASK 0x000f
++
++/**
++ * struct utrace_attached_engine - per-engine structure
++ * @ops: &struct utrace_engine_ops pointer passed to utrace_attach_task()
++ * @data: engine-private &void * passed to utrace_attach_task()
++ * @flags: event mask set by utrace_set_events() plus internal flag bits
++ *
++ * The task itself never has to worry about engines detaching while
++ * it's doing event callbacks. These structures are removed from the
++ * task's active list only when it's stopped, or by the task itself.
++ *
++ * utrace_engine_get() and utrace_engine_put() maintain a reference count.
++ * When it drops to zero, the structure is freed. One reference is held
++ * implicitly while the engine is attached to its task.
++ */
++struct utrace_attached_engine {
++/* private: */
++ struct kref kref;
++ struct list_head entry;
++
++/* public: */
++ const struct utrace_engine_ops *ops;
++ void *data;
++
++ unsigned long flags;
++};
++
++/**
++ * utrace_engine_get - acquire a reference on a &struct utrace_attached_engine
++ * @engine: &struct utrace_attached_engine pointer
++ *
++ * You must hold a reference on @engine, and you get another.
++ */
++static inline void utrace_engine_get(struct utrace_attached_engine *engine)
++{
++ kref_get(&engine->kref);
++}
++
++/**
++ * utrace_engine_put - release a reference on a &struct utrace_attached_engine
++ * @engine: &struct utrace_attached_engine pointer
++ *
++ * You must hold a reference on @engine, and you lose that reference.
++ * If it was the last one, @engine becomes an invalid pointer.
++ */
++static inline void utrace_engine_put(struct utrace_attached_engine *engine)
++{
++ kref_put(&engine->kref, __utrace_engine_release);
++}
++
++/**
++ * struct utrace_engine_ops - tracing engine callbacks
++ *
++ * Each @report_*() callback corresponds to an %UTRACE_EVENT(*) bit.
++ * utrace_set_events() calls on @engine choose which callbacks will be made
++ * to @engine from @task.
++ *
++ * Most callbacks take an @action argument, giving the resume action
++ * chosen by other tracing engines. All callbacks take an @engine
++ * argument, and a @task argument, which is always equal to @current.
++ * For some calls, @action also includes bits specific to that event
++ * and utrace_resume_action() is used to extract the resume action.
++ * This shows what would happen if @engine wasn't there, or will if
++ * the callback's return value uses %UTRACE_RESUME. This always
++ * starts as %UTRACE_RESUME when no other tracing is being done on
++ * this task.
++ *
++ * All return values contain &enum utrace_resume_action bits. For
++ * some calls, other bits specific to that kind of event are added to
++ * the resume action bits with OR. These are the same bits used in
++ * the @action argument. The resume action returned by a callback
++ * does not override previous engines' choices, it only says what
++ * @engine wants done. What @task actually does is the action that's
++ * most constrained among the choices made by all attached engines.
++ * See utrace_control() for more information on the actions.
++ *
++ * When %UTRACE_STOP is used in @report_syscall_entry, then @task
++ * stops before attempting the system call. In other cases, the
++ * resume action does not take effect until @task is ready to check
++ * for signals and return to user mode. If there are more callbacks
++ * to be made, the last round of calls determines the final action.
++ * A @report_quiesce callback with @event zero, or a @report_signal
++ * callback, will always be the last one made before @task resumes.
++ * Only %UTRACE_STOP is "sticky"--if @engine returned %UTRACE_STOP
++ * then @task stays stopped unless @engine returns different from a
++ * following callback.
++ *
++ * The report_death() and report_reap() callbacks do not take @action
++ * arguments, and only %UTRACE_DETACH is meaningful in the return value
++ * from a report_death() callback. None of the resume actions applies
++ * to a dead thread.
++ *
++ * All @report_*() hooks are called with no locks held, in a generally
++ * safe environment when we will be returning to user mode soon (or just
++ * entered the kernel). It is fine to block for memory allocation and
++ * the like, but all hooks are asynchronous and must not block on
++ * external events! If you want the thread to block, use %UTRACE_STOP
++ * in your hook's return value; then later wake it up with utrace_control().
++ *
++ * The @unsafe_exec and @tracer_task hooks are not associated with
++ * event reports. These may be %NULL if the engine has nothing to say.
++ * These hooks are called in more constrained environments and should
++ * not block or do very much.
++ *
++ * @report_quiesce:
++ * Requested by %UTRACE_EVENT(%QUIESCE).
++ * This does not indicate any event, but just that @task (the current
++ * thread) is in a safe place for examination. This call is made
++ * before each specific event callback, except for @report_reap.
++ * The @event argument gives the %UTRACE_EVENT(@which) value for
++ * the event occurring. This callback might be made for events @engine
++ * has not requested, if some other engine is tracing the event;
++ * calling utrace_set_events() call here can request the immediate
++ * callback for this occurrence of @event. @event is zero when there
++ * is no other event, @task is now ready to check for signals and
++ * return to user mode, and some engine has used %UTRACE_REPORT or
++ * %UTRACE_INTERRUPT to request this callback. For this case,
++ * if @report_signal is not %NULL, the @report_quiesce callback
++ * may be replaced with a @report_signal callback passing
++ * %UTRACE_SIGNAL_REPORT in its @action argument, whenever @task is
++ * entering the signal-check path anyway.
++ *
++ * @report_signal:
++ * Requested by %UTRACE_EVENT(%SIGNAL_*) or %UTRACE_EVENT(%QUIESCE).
++ * Use utrace_signal_action() and utrace_resume_action() on @action.
++ * The signal action is %UTRACE_SIGNAL_REPORT when some engine has
++ * used %UTRACE_REPORT or %UTRACE_INTERRUPT; the callback can choose
++ * to stop or to deliver an artificial signal, before pending signals.
++ * It's %UTRACE_SIGNAL_HANDLER instead when signal handler setup just
++ * finished (after a previous %UTRACE_SIGNAL_DELIVER return); this
++ * serves in lieu of any %UTRACE_SIGNAL_REPORT callback requested by
++ * %UTRACE_REPORT or %UTRACE_INTERRUPT, and is also implicitly
++ * requested by %UTRACE_SINGLESTEP or %UTRACE_BLOCKSTEP into the
++ * signal delivery. The other signal actions indicate a signal about
++ * to be delivered; the previous engine's return value sets the signal
++ * action seen by the the following engine's callback. The @info data
++ * can be changed at will, including @info->si_signo. The settings in
++ * @return_ka determines what %UTRACE_SIGNAL_DELIVER does. @orig_ka
++ * is what was in force before other tracing engines intervened, and
++ * it's %NULL when this report began as %UTRACE_SIGNAL_REPORT or
++ * %UTRACE_SIGNAL_HANDLER. For a report without a new signal, @info
++ * is left uninitialized and must be set completely by an engine that
++ * chooses to deliver a signal; if there was a previous @report_signal
++ * callback ending in %UTRACE_STOP and it was just resumed using
++ * %UTRACE_REPORT or %UTRACE_INTERRUPT, then @info is left unchanged
++ * from the previous callback. In this way, the original signal can
++ * be left in @info while returning %UTRACE_STOP|%UTRACE_SIGNAL_IGN
++ * and then found again when resuming @task with %UTRACE_INTERRUPT.
++ * The %UTRACE_SIGNAL_HOLD flag bit can be OR'd into the return value,
++ * and might be in @action if the previous engine returned it. This
++ * flag asks that the signal in @info be pushed back on @task's queue
++ * so that it will be seen again after whatever action is taken now.
++ *
++ * @report_clone:
++ * Requested by %UTRACE_EVENT(%CLONE).
++ * Event reported for parent, before the new task @child might run.
++ * @clone_flags gives the flags used in the clone system call,
++ * or equivalent flags for a fork() or vfork() system call.
++ * This function can use utrace_attach_task() on @child. It's guaranteed
++ * that asynchronous utrace_attach_task() calls will be ordered after
++ * any calls in @report_clone callbacks for the parent. Thus
++ * when using %UTRACE_ATTACH_EXCLUSIVE in the asynchronous calls,
++ * you can be sure that the parent's @report_clone callback has
++ * already attached to @child or chosen not to. Passing %UTRACE_STOP
++ * to utrace_control() on @child here keeps the child stopped before
++ * it ever runs in user mode, %UTRACE_REPORT or %UTRACE_INTERRUPT
++ * ensures a callback from @child before it starts in user mode.
++ *
++ * @report_jctl:
++ * Requested by %UTRACE_EVENT(%JCTL).
++ * Job control event; @type is %CLD_STOPPED or %CLD_CONTINUED,
++ * indicating whether we are stopping or resuming now. If @notify
++ * is nonzero, @task is the last thread to stop and so will send
++ * %SIGCHLD to its parent after this callback; @notify reflects
++ * what the parent's %SIGCHLD has in @si_code, which can sometimes
++ * be %CLD_STOPPED even when @type is %CLD_CONTINUED.
++ *
++ * @report_exec:
++ * Requested by %UTRACE_EVENT(%EXEC).
++ * An execve system call has succeeded and the new program is about to
++ * start running. The initial user register state is handy to be tweaked
++ * directly in @regs. @fmt and @bprm gives the details of this exec.
++ *
++ * @report_syscall_entry:
++ * Requested by %UTRACE_EVENT(%SYSCALL_ENTRY).
++ * Thread has entered the kernel to request a system call.
++ * The user register state is handy to be tweaked directly in @regs.
++ * The @action argument contains an &enum utrace_syscall_action,
++ * use utrace_syscall_action() to extract it. The return value
++ * overrides the last engine's action for the system call.
++ * If the final action is %UTRACE_SYSCALL_ABORT, no system call
++ * is made. The details of the system call being attempted can
++ * be fetched here with syscall_get_nr() and syscall_get_arguments().
++ * The parameter registers can be changed with syscall_set_arguments().
++ *
++ * @report_syscall_exit:
++ * Requested by %UTRACE_EVENT(%SYSCALL_EXIT).
++ * Thread is about to leave the kernel after a system call request.
++ * The user register state is handy to be tweaked directly in @regs.
++ * The results of the system call attempt can be examined here using
++ * syscall_get_error() and syscall_get_return_value(). It is safe
++ * here to call syscall_set_return_value() or syscall_rollback().
++ *
++ * @report_exit:
++ * Requested by %UTRACE_EVENT(%EXIT).
++ * Thread is exiting and cannot be prevented from doing so,
++ * but all its state is still live. The @code value will be
++ * the wait result seen by the parent, and can be changed by
++ * this engine or others. The @orig_code value is the real
++ * status, not changed by any tracing engine. Returning %UTRACE_STOP
++ * here keeps @task stopped before it cleans up its state and dies,
++ * so it can be examined by other processes. When @task is allowed
++ * to run, it will die and get to the @report_death callback.
++ *
++ * @report_death:
++ * Requested by %UTRACE_EVENT(%DEATH).
++ * Thread is really dead now. It might be reaped by its parent at
++ * any time, or self-reap immediately. Though the actual reaping
++ * may happen in parallel, a report_reap() callback will always be
++ * ordered after a report_death() callback.
++ *
++ * @report_reap:
++ * Requested by %UTRACE_EVENT(%REAP).
++ * Called when someone reaps the dead task (parent, init, or self).
++ * This means the parent called wait, or else this was a detached
++ * thread or a process whose parent ignores SIGCHLD.
++ * No more callbacks are made after this one.
++ * The engine is always detached.
++ * There is nothing more a tracing engine can do about this thread.
++ * After this callback, the @engine pointer will become invalid.
++ * The @task pointer may become invalid if get_task_struct() hasn't
++ * been used to keep it alive.
++ * An engine should always request this callback if it stores the
++ * @engine pointer or stores any pointer in @engine->data, so it
++ * can clean up its data structures.
++ * Unlike other callbacks, this can be called from the parent's context
++ * rather than from the traced thread itself--it must not delay the
++ * parent by blocking.
++ *
++ * @unsafe_exec:
++ * Used if not %NULL.
++ * Return %LSM_UNSAFE_* bits that apply to the exec in progress
++ * due to tracing done by this engine. These bits indicate that
++ * someone is able to examine the process and so a set-UID or similar
++ * privilege escalation may not be safe to permit.
++ * Called with task_lock() held.
++ *
++ * @tracer_task:
++ * Used if not %NULL.
++ * Return the &struct task_struct for the task using ptrace() on
++ * @task, or %NULL. Always called with rcu_read_lock() held to
++ * keep the returned struct alive. At exec time, this may be
++ * called with task_lock() still held from when unsafe_exec() was
++ * just called. In that case it must give results consistent
++ * with those unsafe_exec() results, i.e. non-%NULL if any
++ * %LSM_UNSAFE_PTRACE_* bits were set. The value is also used to
++ * display after "TracerPid:" in /proc/PID/status, where it is
++ * called with only rcu_read_lock() held. If this engine returns
++ * %NULL, another engine may supply the result.
++ */
++struct utrace_engine_ops {
++ u32 (*report_quiesce)(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ unsigned long event);
++ u32 (*report_signal)(u32 action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ struct pt_regs *regs,
++ siginfo_t *info,
++ const struct k_sigaction *orig_ka,
++ struct k_sigaction *return_ka);
++ u32 (*report_clone)(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *parent,
++ unsigned long clone_flags,
++ struct task_struct *child);
++ u32 (*report_jctl)(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ int type, int notify);
++ u32 (*report_exec)(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ const struct linux_binfmt *fmt,
++ const struct linux_binprm *bprm,
++ struct pt_regs *regs);
++ u32 (*report_syscall_entry)(u32 action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ struct pt_regs *regs);
++ u32 (*report_syscall_exit)(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ struct pt_regs *regs);
++ u32 (*report_exit)(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ long orig_code, long *code);
++ u32 (*report_death)(struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ bool group_dead, int signal);
++ void (*report_reap)(struct utrace_attached_engine *engine,
++ struct task_struct *task);
++
++ int (*unsafe_exec)(struct utrace_attached_engine *engine,
++ struct task_struct *task);
++ struct task_struct *(*tracer_task)(
++ struct utrace_attached_engine *engine,
++ struct task_struct *task);
++};
++
++/**
++ * struct utrace_examiner - private state for using utrace_prepare_examine()
++ * @dummy: all fields are private, none described here
++ *
++ * The members of &struct utrace_examiner are private to the implementation.
++ * This data type holds the state from a call to utrace_prepare_examine()
++ * to be used by a call to utrace_finish_examine().
++ */
++struct utrace_examiner {
++/* private: */
++ long state; /* cache of task_struct.state */
++ unsigned long ncsw; /* cache of wait_task_inactive() return value */
++/* public: */
++ struct {} dummy;
++};
++
++/**
++ * utrace_control_pid - control a thread being traced by a tracing engine
++ * @pid: thread to affect
++ * @engine: attached engine to affect
++ * @action: &enum utrace_resume_action for thread to do
++ *
++ * This is the same as utrace_control(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer. The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid. If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++static inline __must_check int utrace_control_pid(
++ struct pid *pid, struct utrace_attached_engine *engine,
++ enum utrace_resume_action action)
++{
++ /*
++ * We don't bother with rcu_read_lock() here to protect the
++ * task_struct pointer, because utrace_control will return
++ * -ESRCH without looking at that pointer if the engine is
++ * already detached. A task_struct pointer can't die before
++ * all the engines are detached in release_task() first.
++ */
++ struct task_struct *task = pid_task(pid, PIDTYPE_PID);
++ return unlikely(!task) ? -ESRCH : utrace_control(task, engine, action);
++}
++
++/**
++ * utrace_set_events_pid - choose which event reports a tracing engine gets
++ * @pid: thread to affect
++ * @engine: attached engine to affect
++ * @eventmask: new event mask
++ *
++ * This is the same as utrace_set_events(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer. The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid. If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++static inline __must_check int utrace_set_events_pid(
++ struct pid *pid, struct utrace_attached_engine *engine,
++ unsigned long eventmask)
++{
++ struct task_struct *task = pid_task(pid, PIDTYPE_PID);
++ return unlikely(!task) ? -ESRCH :
++ utrace_set_events(task, engine, eventmask);
++}
++
++/**
++ * utrace_barrier_pid - synchronize with simultaneous tracing callbacks
++ * @pid: thread to affect
++ * @engine: engine to affect (can be detached)
++ *
++ * This is the same as utrace_barrier(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer. The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid. If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++static inline __must_check int utrace_barrier_pid(
++ struct pid *pid, struct utrace_attached_engine *engine)
++{
++ struct task_struct *task = pid_task(pid, PIDTYPE_PID);
++ return unlikely(!task) ? -ESRCH : utrace_barrier(task, engine);
++}
++
++#endif /* CONFIG_UTRACE */
++
++#endif /* linux/utrace.h */
+--- a/init/Kconfig
++++ b/init/Kconfig
+@@ -916,6 +916,16 @@ config STOP_MACHINE
+ help
+ Need stop_machine() primitive.
+
++menuconfig UTRACE
++ bool "Infrastructure for tracing and debugging user processes"
++ depends on EXPERIMENTAL
++ depends on HAVE_ARCH_TRACEHOOK
++ depends on MODULES
++ help
++ Enable the utrace process tracing interface. This is an internal
++ kernel interface exported to kernel modules, to track events in
++ user threads, extract and change user thread state.
++
+ source "block/Kconfig"
+
+ config PREEMPT_NOTIFIERS
+--- a/kernel/Makefile
++++ b/kernel/Makefile
+@@ -65,6 +65,7 @@ obj-$(CONFIG_IKCONFIG) += configs.o
+ obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
+ obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
+ obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
++obj-$(CONFIG_UTRACE) += utrace.o
+ obj-$(CONFIG_AUDIT) += audit.o auditfilter.o
+ obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
+ obj-$(CONFIG_AUDIT_TREE) += audit_tree.o
+--- /dev/null
++++ b/kernel/utrace.c
+@@ -0,0 +1,2495 @@
++/*
++ * utrace infrastructure interface for debugging user processes
++ *
++ * Copyright (C) 2006, 2007, 2008 Red Hat, Inc. All rights reserved.
++ *
++ * This copyrighted material is made available to anyone wishing to use,
++ * modify, copy, or redistribute it subject to the terms and conditions
++ * of the GNU General Public License v.2.
++ *
++ * Red Hat Author: Roland McGrath.
++ */
++
++#include <linux/utrace.h>
++#include <linux/tracehook.h>
++#include <linux/regset.h>
++#include <asm/syscall.h>
++#include <linux/ptrace.h>
++#include <linux/err.h>
++#include <linux/sched.h>
++#include <linux/freezer.h>
++#include <linux/module.h>
++#include <linux/init.h>
++#include <linux/slab.h>
++#include <linux/seq_file.h>
++
++
++#define UTRACE_DEBUG 1
++#ifdef UTRACE_DEBUG
++#define CHECK_INIT(p) atomic_set(&(p)->check_dead, 1)
++#define CHECK_DEAD(p) BUG_ON(!atomic_dec_and_test(&(p)->check_dead))
++#else
++#define CHECK_INIT(p) do { } while (0)
++#define CHECK_DEAD(p) do { } while (0)
++#endif
++
++/*
++ * Per-thread structure task_struct.utrace points to.
++ *
++ * The task itself never has to worry about this going away after
++ * some event is found set in task_struct.utrace_flags.
++ * Once created, this pointer is changed only when the task is quiescent
++ * (TASK_TRACED or TASK_STOPPED with the siglock held, or dead).
++ *
++ * For other parties, the pointer to this is protected by RCU and
++ * task_lock. Since call_rcu is never used while the thread is alive and
++ * using this struct utrace, we can overlay the RCU data structure used
++ * only for a dead struct with some local state used only for a live utrace
++ * on an active thread.
++ *
++ * The two lists @attached and @attaching work together for smooth
++ * asynchronous attaching with low overhead. Modifying either list
++ * requires @lock. The @attaching list can be modified any time while
++ * holding @lock. New engines being attached always go on this list.
++ *
++ * The @attached list is what the task itself uses for its reporting
++ * loops. When the task itself is not quiescent, it can use the
++ * @attached list without taking any lock. Noone may modify the list
++ * when the task is not quiescent. When it is quiescent, that means
++ * that it won't run again without taking @lock itself before using
++ * the list.
++ *
++ * At each place where we know the task is quiescent (or it's current),
++ * while holding @lock, we call splice_attaching(), below. This moves
++ * the @attaching list members on to the end of the @attached list.
++ * Since this happens at the start of any reporting pass, any new
++ * engines attached asynchronously go on the stable @attached list
++ * in time to have their callbacks seen.
++ */
++struct utrace {
++ union {
++ struct rcu_head dead;
++ struct {
++ struct task_struct *cloning;
++ } live;
++ } u;
++
++ struct list_head attached, attaching;
++ spinlock_t lock;
++#ifdef UTRACE_DEBUG
++ atomic_t check_dead;
++#endif
++
++ struct utrace_attached_engine *reporting;
++
++ unsigned int stopped:1;
++ unsigned int report:1;
++ unsigned int interrupt:1;
++ unsigned int signal_handler:1;
++ unsigned int death:1; /* in utrace_report_death() now */
++ unsigned int reap:1; /* release_task() has run */
++};
++
++static struct kmem_cache *utrace_cachep;
++static struct kmem_cache *utrace_engine_cachep;
++static const struct utrace_engine_ops utrace_detached_ops; /* forward decl */
++
++static int __init utrace_init(void)
++{
++ utrace_cachep = KMEM_CACHE(utrace, SLAB_PANIC);
++ utrace_engine_cachep = KMEM_CACHE(utrace_attached_engine, SLAB_PANIC);
++ return 0;
++}
++subsys_initcall(utrace_init);
++
++
++/*
++ * Make sure target->utrace is allocated, and return with it locked on
++ * success. This function mediates startup races. The creating parent
++ * task has priority, and other callers will delay here to let its call
++ * succeed and take the new utrace lock first.
++ */
++static struct utrace *utrace_first_engine(struct task_struct *target,
++ struct utrace_attached_engine *engine)
++ __acquires(utrace->lock)
++{
++ struct utrace *utrace;
++
++ /*
++ * If this is a newborn thread and we are not the creator,
++ * we have to wait for it. The creator gets the first chance
++ * to attach. The PF_STARTING flag is cleared after its
++ * report_clone hook has had a chance to run.
++ */
++ if (target->flags & PF_STARTING) {
++ utrace = current->utrace;
++ if (utrace == NULL || utrace->u.live.cloning != target) {
++ yield();
++ if (signal_pending(current))
++ return ERR_PTR(-ERESTARTNOINTR);
++ return NULL;
++ }
++ }
++
++ utrace = kmem_cache_zalloc(utrace_cachep, GFP_KERNEL);
++ if (unlikely(utrace == NULL))
++ return ERR_PTR(-ENOMEM);
++
++ INIT_LIST_HEAD(&utrace->attached);
++ INIT_LIST_HEAD(&utrace->attaching);
++ list_add(&engine->entry, &utrace->attached);
++ spin_lock_init(&utrace->lock);
++ CHECK_INIT(utrace);
++
++ spin_lock(&utrace->lock);
++ task_lock(target);
++ if (likely(target->utrace == NULL)) {
++ rcu_assign_pointer(target->utrace, utrace);
++
++ /*
++ * The task_lock protects us against another thread doing
++ * the same thing. We might still be racing against
++ * tracehook_release_task. It's called with ->exit_state
++ * set to EXIT_DEAD and then checks ->utrace with an
++ * smp_mb() in between. If EXIT_DEAD is set, then
++ * release_task might have checked ->utrace already and saw
++ * it NULL; we can't attach. If we see EXIT_DEAD not yet
++ * set after our barrier, then we know release_task will
++ * see our target->utrace pointer.
++ */
++ smp_mb();
++ if (likely(target->exit_state != EXIT_DEAD)) {
++ task_unlock(target);
++ return utrace;
++ }
++
++ /*
++ * The target has already been through release_task.
++ * Our caller will restart and notice it's too late now.
++ */
++ target->utrace = NULL;
++ }
++
++ /*
++ * Another engine attached first, so there is a struct already.
++ * A null return says to restart looking for the existing one.
++ */
++ task_unlock(target);
++ spin_unlock(&utrace->lock);
++ kmem_cache_free(utrace_cachep, utrace);
++
++ return NULL;
++}
++
++static void utrace_free(struct rcu_head *rhead)
++{
++ struct utrace *utrace = container_of(rhead, struct utrace, u.dead);
++ kmem_cache_free(utrace_cachep, utrace);
++}
++
++/*
++ * Called with utrace locked. Clean it up and free it via RCU.
++ */
++static void rcu_utrace_free(struct utrace *utrace)
++ __releases(utrace->lock)
++{
++ CHECK_DEAD(utrace);
++ spin_unlock(&utrace->lock);
++ call_rcu(&utrace->u.dead, utrace_free);
++}
++
++/*
++ * This is the exported function used by the utrace_engine_put() inline.
++ */
++void __utrace_engine_release(struct kref *kref)
++{
++ struct utrace_attached_engine *engine =
++ container_of(kref, struct utrace_attached_engine, kref);
++ BUG_ON(!list_empty(&engine->entry));
++ kmem_cache_free(utrace_engine_cachep, engine);
++}
++EXPORT_SYMBOL_GPL(__utrace_engine_release);
++
++static bool engine_matches(struct utrace_attached_engine *engine, int flags,
++ const struct utrace_engine_ops *ops, void *data)
++{
++ if ((flags & UTRACE_ATTACH_MATCH_OPS) && engine->ops != ops)
++ return false;
++ if ((flags & UTRACE_ATTACH_MATCH_DATA) && engine->data != data)
++ return false;
++ return engine->ops && engine->ops != &utrace_detached_ops;
++}
++
++static struct utrace_attached_engine *matching_engine(
++ struct utrace *utrace, int flags,
++ const struct utrace_engine_ops *ops, void *data)
++{
++ struct utrace_attached_engine *engine;
++ list_for_each_entry(engine, &utrace->attached, entry)
++ if (engine_matches(engine, flags, ops, data))
++ return engine;
++ list_for_each_entry(engine, &utrace->attaching, entry)
++ if (engine_matches(engine, flags, ops, data))
++ return engine;
++ return NULL;
++}
++
++/*
++ * Allocate a new engine structure. It starts out with two refs:
++ * one ref for utrace_attach_task() to return, and ref for being attached.
++ */
++static struct utrace_attached_engine *alloc_engine(void)
++{
++ struct utrace_attached_engine *engine;
++ engine = kmem_cache_alloc(utrace_engine_cachep, GFP_KERNEL);
++ if (likely(engine)) {
++ engine->flags = 0;
++ kref_set(&engine->kref, 2);
++ }
++ return engine;
++}
++
++/**
++ * utrace_attach_task - attach new engine, or look up an attached engine
++ * @target: thread to attach to
++ * @flags: flag bits combined with OR, see below
++ * @ops: callback table for new engine
++ * @data: engine private data pointer
++ *
++ * The caller must ensure that the @target thread does not get freed,
++ * i.e. hold a ref or be its parent. It is always safe to call this
++ * on @current, or on the @child pointer in a @report_clone callback.
++ * For most other cases, it's easier to use utrace_attach_pid() instead.
++ *
++ * UTRACE_ATTACH_CREATE:
++ * Create a new engine. If %UTRACE_ATTACH_CREATE is not specified, you
++ * only look up an existing engine already attached to the thread.
++ *
++ * UTRACE_ATTACH_EXCLUSIVE:
++ * Attempting to attach a second (matching) engine fails with -%EEXIST.
++ *
++ * UTRACE_ATTACH_MATCH_OPS: Only consider engines matching @ops.
++ * UTRACE_ATTACH_MATCH_DATA: Only consider engines matching @data.
++ */
++struct utrace_attached_engine *utrace_attach_task(
++ struct task_struct *target, int flags,
++ const struct utrace_engine_ops *ops, void *data)
++{
++ struct utrace *utrace;
++ struct utrace_attached_engine *engine;
++
++restart:
++ rcu_read_lock();
++ utrace = rcu_dereference(target->utrace);
++ smp_rmb();
++ if (unlikely(target->exit_state == EXIT_DEAD)) {
++ /*
++ * The target has already been reaped.
++ * Check this first; a race with reaping may lead to restart.
++ */
++ rcu_read_unlock();
++ if (!(flags & UTRACE_ATTACH_CREATE))
++ return ERR_PTR(-ENOENT);
++ return ERR_PTR(-ESRCH);
++ }
++
++ if (utrace == NULL) {
++ rcu_read_unlock();
++
++ if (!(flags & UTRACE_ATTACH_CREATE))
++ return ERR_PTR(-ENOENT);
++
++ if (unlikely(target->flags & PF_KTHREAD))
++ /*
++ * Silly kernel, utrace is for users!
++ */
++ return ERR_PTR(-EPERM);
++
++ engine = alloc_engine();
++ if (unlikely(!engine))
++ return ERR_PTR(-ENOMEM);
++
++ goto first;
++ }
++
++ if (!(flags & UTRACE_ATTACH_CREATE)) {
++ spin_lock(&utrace->lock);
++ engine = matching_engine(utrace, flags, ops, data);
++ if (engine)
++ utrace_engine_get(engine);
++ spin_unlock(&utrace->lock);
++ rcu_read_unlock();
++ return engine ?: ERR_PTR(-ENOENT);
++ }
++ rcu_read_unlock();
++
++ if (unlikely(!ops) || unlikely(ops == &utrace_detached_ops))
++ return ERR_PTR(-EINVAL);
++
++ engine = alloc_engine();
++ if (unlikely(!engine))
++ return ERR_PTR(-ENOMEM);
++
++ rcu_read_lock();
++ utrace = rcu_dereference(target->utrace);
++ if (unlikely(utrace == NULL)) { /* Race with detach. */
++ rcu_read_unlock();
++ goto first;
++ }
++ spin_lock(&utrace->lock);
++
++ if (flags & UTRACE_ATTACH_EXCLUSIVE) {
++ struct utrace_attached_engine *old;
++ old = matching_engine(utrace, flags, ops, data);
++ if (old) {
++ spin_unlock(&utrace->lock);
++ rcu_read_unlock();
++ kmem_cache_free(utrace_engine_cachep, engine);
++ return ERR_PTR(-EEXIST);
++ }
++ }
++
++ if (unlikely(rcu_dereference(target->utrace) != utrace)) {
++ /*
++ * We lost a race with other CPUs doing a sequence
++ * of detach and attach before we got in.
++ */
++ spin_unlock(&utrace->lock);
++ rcu_read_unlock();
++ kmem_cache_free(utrace_engine_cachep, engine);
++ goto restart;
++ }
++ rcu_read_unlock();
++
++ list_add_tail(&engine->entry, &utrace->attaching);
++ utrace->report = 1;
++ goto finish;
++
++first:
++ utrace = utrace_first_engine(target, engine);
++ if (IS_ERR(utrace) || unlikely(utrace == NULL)) {
++ kmem_cache_free(utrace_engine_cachep, engine);
++ if (unlikely(utrace == NULL)) /* Race condition. */
++ goto restart;
++ return ERR_PTR(PTR_ERR(utrace));
++ }
++
++finish:
++ engine->ops = ops;
++ engine->data = data;
++
++ spin_unlock(&utrace->lock);
++
++ return engine;
++}
++EXPORT_SYMBOL_GPL(utrace_attach_task);
++
++/**
++ * utrace_attach_pid - attach new engine, or look up an attached engine
++ * @pid: &struct pid pointer representing thread to attach to
++ * @flags: flag bits combined with OR, see utrace_attach_task()
++ * @ops: callback table for new engine
++ * @data: engine private data pointer
++ *
++ * This is the same as utrace_attach_task(), but takes a &struct pid
++ * pointer rather than a &struct task_struct pointer. The caller must
++ * hold a ref on @pid, but does not need to worry about the task
++ * staying valid. If it's been reaped so that @pid points nowhere,
++ * then this call returns -%ESRCH.
++ */
++struct utrace_attached_engine *utrace_attach_pid(
++ struct pid *pid, int flags,
++ const struct utrace_engine_ops *ops, void *data)
++{
++ struct utrace_attached_engine *engine = ERR_PTR(-ESRCH);
++ struct task_struct *task = get_pid_task(pid, PIDTYPE_PID);
++ if (task) {
++ engine = utrace_attach_task(task, flags, ops, data);
++ put_task_struct(task);
++ }
++ return engine;
++}
++EXPORT_SYMBOL_GPL(utrace_attach_pid);
++
++/*
++ * This is called with @utrace->lock held when the task is safely
++ * quiescent, i.e. it won't consult utrace->attached without the lock.
++ * Move any engines attached asynchronously from @utrace->attaching
++ * onto the @utrace->attached list.
++ */
++static void splice_attaching(struct utrace *utrace)
++{
++ list_splice_tail_init(&utrace->attaching, &utrace->attached);
++}
++
++/*
++ * When an engine is detached, the target thread may still see it and
++ * make callbacks until it quiesces. We install a special ops vector
++ * with these two callbacks. When the target thread quiesces, it can
++ * safely free the engine itself. For any event we will always get
++ * the report_quiesce() callback first, so we only need this one
++ * pointer to be set. The only exception is report_reap(), so we
++ * supply that callback too.
++ */
++static u32 utrace_detached_quiesce(enum utrace_resume_action action,
++ struct utrace_attached_engine *engine,
++ struct task_struct *task,
++ unsigned long event)
++{
++ return UTRACE_DETACH;
++}
++
++static void utrace_detached_reap(struct utrace_attached_engine *engine,
++ struct task_struct *task)
++{
++}
++
++static const struct utrace_engine_ops utrace_detached_ops = {
++ .report_quiesce = &utrace_detached_quiesce,
++ .report_reap = &utrace_detached_reap
++};
++
++/*
++ * Only these flags matter any more for a dead task (exit_state set).
++ * We use this mask on flags installed in ->utrace_flags after
++ * exit_notify (and possibly utrace_report_death) has run.
++ * This ensures that utrace_release_task knows positively that
++ * utrace_report_death will not run later.
++ */
++#define DEAD_FLAGS_MASK (UTRACE_EVENT(REAP))
++#define LIVE_FLAGS_MASK (~0UL)
++
++/*
++ * Perform %UTRACE_STOP, i.e. block in TASK_TRACED until woken up.
++ * @task == current, @utrace == current->utrace, which is not locked.
++ * Return true if we were woken up by SIGKILL even though some utrace
++ * engine may still want us to stay stopped.
++ */
++static bool utrace_stop(struct task_struct *task, struct utrace *utrace)
++{
++ /*
++ * @utrace->stopped is the flag that says we are safely
++ * inside this function. It should never be set on entry.
++ */
++ BUG_ON(utrace->stopped);
++
++ /*
++ * The siglock protects us against signals. As well as SIGKILL
++ * waking us up, we must synchronize with the signal bookkeeping
++ * for stop signals and SIGCONT.
++ */
++ spin_lock(&utrace->lock);
++ spin_lock_irq(&task->sighand->siglock);
++
++ if (unlikely(sigismember(&task->pending.signal, SIGKILL))) {
++ spin_unlock_irq(&task->sighand->siglock);
++ spin_unlock(&utrace->lock);
++ return true;
++ }
++
++ utrace->stopped = 1;
++ __set_current_state(TASK_TRACED);
++
++ /*
++ * If there is a group stop in progress,
++ * we must participate in the bookkeeping.
++ */
++ if (task->signal->group_stop_count > 0)
++ --task->signal->group_stop_count;
++
++ spin_unlock_irq(&task->sighand->siglock);
++ spin_unlock(&utrace->lock);
++
++ schedule();
++
++ /*
++ * While in TASK_TRACED, we were considered "frozen enough".
++ * Now that we woke up, it's crucial if we're supposed to be
++ * frozen that we freeze now before running anything substantial.
++ */
++ try_to_freeze();
++
++ /*
++ * utrace_wakeup() clears @utrace->stopped before waking us up.
++ * We're officially awake if it's clear.
++ */
++ if (likely(!utrace->stopped))
++ return false;
++
++ /*
++ * If we're here with it still set, it must have been
++ * signal_wake_up() instead, waking us up for a SIGKILL.
++ */
++ spin_lock(&utrace->lock);
++ utrace->stopped = 0;
++ spin_unlock(&utrace->lock);
++ return true;
++}
++
++/*
++ * The caller has to hold a ref on the engine. If the attached flag is
++ * true (all but utrace_barrier() calls), the engine is supposed to be
++ * attached. If the attached flag is false (utrace_barrier() only),
++ * then return -ERESTARTSYS for an engine marked for detach but not yet
++ * fully detached. The task pointer can be invalid if the engine is
++ * detached.
++ *
++ * Get the utrace lock for the target task.
++ * Returns the struct if locked, or ERR_PTR(-errno).
++ *
++ * This has to be robust against races with:
++ * utrace_control(target, UTRACE_DETACH) calls
++ * UTRACE_DETACH after reports
++ * utrace_report_death
++ * utrace_release_task
++ */
++static struct utrace *get_utrace_lock(struct task_struct *target,
++ struct utrace_attached_engine *engine,
++ bool attached)
++ __acquires(utrace->lock)
++{
++ struct utrace *utrace;
++
++ /*
++ * You must hold a ref to be making a call. A call from within
++ * a report_* callback in @target might only have the ref for
++ * being attached, not a second one of its own.
++ */
++ if (unlikely(atomic_read(&engine->kref.refcount) < 1))
++ return ERR_PTR(-EINVAL);
++
++ rcu_read_lock();
++
++ /*
++ * If this engine was already detached, bail out before we look at
++ * the task_struct pointer at all. If it's detached after this
++ * check, then RCU is still keeping this task_struct pointer valid.
++ *
++ * The ops pointer is NULL when the engine is fully detached.
++ * It's &utrace_detached_ops when it's marked detached but still
++ * on the list. In the latter case, utrace_barrier() still works,
++ * since the target might be in the middle of an old callback.
++ */
++ if (unlikely(!engine->ops)) {
++ rcu_read_unlock();
++ return ERR_PTR(-ESRCH);
++ }
++
++ if (unlikely(engine->ops == &utrace_detached_ops)) {
++ rcu_read_unlock();
++ return attached ? ERR_PTR(-ESRCH) : ERR_PTR(-ERESTARTSYS);
++ }
++
++ utrace = rcu_dereference(target->utrace);
++ smp_rmb();
++ if (unlikely(!utrace) || unlikely(target->exit_state == EXIT_DEAD)) {
++ /*
++ * If all engines detached already, utrace is clear.
++ * Otherwise, we're called after utrace_release_task might
++ * have started. A call to this engine's report_reap
++ * callback might already be in progress.
++ */
++ utrace = ERR_PTR(-ESRCH);
++ } else {
++ spin_lock(&utrace->lock);
++ if (unlikely(rcu_dereference(target->utrace) != utrace) ||
++ unlikely(!engine->ops) ||
++ unlikely(engine->ops == &utrace_detached_ops)) {
++ /*
++ * By the time we got the utrace lock,
++ * it had been reaped or detached already.
++ */
++ spin_unlock(&utrace->lock);
++ utrace = ERR_PTR(-ESRCH);
++ if (!attached && engine->ops == &utrace_detached_ops)
++ utrace = ERR_PTR(-ERESTARTSYS);
++ }
++ }
++ rcu_read_unlock();
++
++ return utrace;
++}
++
++/*
++ * Now that we don't hold any locks, run through any
++ * detached engines and free their references. Each
++ * engine had one implicit ref while it was attached.
++ */
++static void put_detached_list(struct list_head *list)
++{
++ struct utrace_attached_engine *engine, *next;
++ list_for_each_entry_safe(engine, next, list, entry) {
++ list_del_init(&engine->entry);
++ utrace_engine_put(engine);
++ }
++}
++
++/*
++ * Called with utrace->lock held.
++ * Notify and clean up all engines, then free utrace.
++ */
++static void utrace_reap(struct task_struct *target, struct utrace *utrace)
++ __releases(utrace->lock)
++{
++ struct utrace_attached_engine *engine, *next;
++ const struct utrace_engine_ops *ops;
++ LIST_HEAD(detached);
++
++restart:
++ splice_attaching(utrace);
++ list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
++ ops = engine->ops;
++ engine->ops = NULL;
++ list_move(&engine->entry, &detached);
++
++ /*
++ * If it didn't need a callback, we don't need to drop
++ * the lock. Now nothing else refers to this engine.
++ */
++ if (!(engine->flags & UTRACE_EVENT(REAP)))
++ continue;
++
++ utrace->reporting = engine;
++ spin_unlock(&utrace->lock);
++
++ (*ops->report_reap)(engine, target);
++
++ utrace->reporting = NULL;
++
++ put_detached_list(&detached);
++
++ spin_lock(&utrace->lock);
++ goto restart;
++ }
++
++ rcu_utrace_free(utrace); /* Releases the lock. */
++
++ put_detached_list(&detached);
++}
++
++#define DEATH_EVENTS (UTRACE_EVENT(DEATH) | UTRACE_EVENT(QUIESCE))
++
++/*
++ * Called by release_task. After this, target->utrace must be cleared.
++ */
++void utrace_release_task(struct task_struct *target)
++{
++ struct utrace *utrace;
++
++ task_lock(target);
++ utrace = rcu_dereference(target->utrace);
++ rcu_assign_pointer(target->utrace, NULL);
++ task_unlock(target);
++
++ if (unlikely(utrace == NULL))
++ return;
++
++ spin_lock(&utrace->lock);
++ /*
++ * If the list is empty, utrace is already on its way to be freed.
++ * We raced with detach and we won the task_lock race but lost the
++ * utrace->lock race. All we have to do is let RCU run.
++ */
++ if (likely(!list_empty(&utrace->attached))) {
++ utrace->reap = 1;
++
++ if (!(target->utrace_flags & DEATH_EVENTS)) {
++ utrace_reap(target, utrace); /* Unlocks and frees. */
++ return;
++ }
++
++ /*
++ * The target will do some final callbacks but hasn't
++ * finished them yet. We know because it clears these
++ * event bits after it's done. Instead of cleaning up here
++ * and requiring utrace_report_death to cope with it, we
++ * delay the REAP report and the teardown until after the
++ * target finishes its death reports.
++ */
++ }
++ spin_unlock(&utrace->lock);
++}
++
++/*
++ * We use an extra bit in utrace_attached_engine.flags past the event bits,
++ * to record whether the engine is keeping the target thread stopped.
++ */
++#define ENGINE_STOP (1UL << _UTRACE_NEVENTS)
++
++static void mark_engine_wants_stop(struct utrace_attached_engine *engine)
++{
++ engine->flags |= ENGINE_STOP;
++}
++
++static void clear_engine_wants_stop(struct utrace_attached_engine *engine)
++{
++ engine->flags &= ~ENGINE_STOP;
++}
++
++static bool engine_wants_stop(struct utrace_attached_engine *engine)
++{
++ return (engine->flags & ENGINE_STOP) != 0;
++}
++
++/**
++ * utrace_set_events - choose which event reports a tracing engine gets
++ * @target: thread to affect
++ * @engine: attached engine to affect
++ * @events: new event mask
++ *
++ * This changes the set of events for which @engine wants callbacks made.
++ *
++ * This fails with -%EALREADY and does nothing if you try to clear
++ * %UTRACE_EVENT(%DEATH) when the @report_death callback may already have
++ * begun, if you try to clear %UTRACE_EVENT(%REAP) when the @report_reap
++ * callback may already have begun, or if you try to newly set
++ * %UTRACE_EVENT(%DEATH) or %UTRACE_EVENT(%QUIESCE) when @target is
++ * already dead or dying.
++ *
++ * This can fail with -%ESRCH when @target has already been detached,
++ * including forcible detach on reaping.
++ *
++ * If @target was stopped before the call, then after a successful call,
++ * no event callbacks not requested in @events will be made; if
++ * %UTRACE_EVENT(%QUIESCE) is included in @events, then a @report_quiesce
++ * callback will be made when @target resumes. If @target was not stopped,
++ * and was about to make a callback to @engine, this returns -%EINPROGRESS.
++ * In this case, the callback in progress might be one excluded from the
++ * new @events setting. When this returns zero, you can be sure that no
++ * event callbacks you've disabled in @events can be made.
++ *
++ * To synchronize after an -%EINPROGRESS return, see utrace_barrier().
++ *
++ * These rules provide for coherent synchronization based on %UTRACE_STOP,
++ * even when %SIGKILL is breaking its normal simple rules.
++ */
++int utrace_set_events(struct task_struct *target,
++ struct utrace_attached_engine *engine,
++ unsigned long events)
++{
++ struct utrace *utrace;
++ unsigned long old_flags, old_utrace_flags, set_utrace_flags;
++ struct sighand_struct *sighand;
++ unsigned long flags;
++ int ret;
++
++ utrace = get_utrace_lock(target, engine, true);
++ if (unlikely(IS_ERR(utrace)))
++ return PTR_ERR(utrace);
++
++ old_utrace_flags = target->utrace_flags;
++ set_utrace_flags = events;
++ old_flags = engine->flags;
++
++ if (target->exit_state &&
++ (((events & ~old_flags) & DEATH_EVENTS) ||
++ (utrace->death && ((old_flags & ~events) & DEATH_EVENTS)) ||
++ (utrace->reap && ((old_flags & ~events) & UTRACE_EVENT(REAP))))) {
++ spin_unlock(&utrace->lock);
++ return -EALREADY;
++ }
++
++ /*
++ * When it's in TASK_STOPPED state and UTRACE_EVENT(JCTL) is set,
++ * utrace_do_stop() will think it is still running and needs to
++ * finish utrace_report_jctl() before it's really stopped. But
++ * if the bit wasn't already set, it can't be running in there
++ * and really is quiescent now in its existing job control stop.
++ */
++ if (!utrace->stopped &&
++ ((set_utrace_flags & ~old_utrace_flags) & UTRACE_EVENT(JCTL))) {
++ sighand = lock_task_sighand(target, &flags);
++ if (likely(sighand)) {
++ if (task_is_stopped(target))
++ utrace->stopped = 1;
++ unlock_task_sighand(target, &flags);
++ }
++ }
++
++ /*
++ * When setting these flags, it's essential that we really
++ * synchronize with exit_notify(). They cannot be set after
++ * exit_notify() takes the tasklist_lock. By holding the read
++ * lock here while setting the flags, we ensure that the calls
++ * to tracehook_notify_death() and tracehook_report_death() will
++ * see the new flags. This ensures that utrace_release_task()
++ * knows positively that utrace_report_death() will be called or
++ * that it won't.
++ */
++ if ((set_utrace_flags & ~old_utrace_flags) & DEATH_EVENTS) {
++ read_lock(&tasklist_lock);
++ if (unlikely(target->exit_state)) {
++ read_unlock(&tasklist_lock);
++ spin_unlock(&utrace->lock);
++ return -EALREADY;
++ }
++ target->utrace_flags |= set_utrace_flags;
++ read_unlock(&tasklist_lock);
++ }
++
++ engine->flags = events | (engine->flags & ENGINE_STOP);
++ target->utrace_flags |= set_utrace_flags;
++
++ if ((set_utrace_flags & UTRACE_EVENT_SYSCALL) &&
++ !(old_utrace_flags & UTRACE_EVENT_SYSCALL))
++ set_tsk_thread_flag(target, TIF_SYSCALL_TRACE);
++
++ ret = 0;
++ if (!utrace->stopped && target != current) {
++ smp_mb();
++ if (utrace->reporting == engine)
++ ret = -EINPROGRESS;
++ }
++
++ spin_unlock(&utrace->lock);
++
++ return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_set_events);
++
++/*
++ * Asynchronously mark an engine as being detached.
++ *
++ * This must work while the target thread races with us doing
++ * start_callback(), defined below. It uses smp_rmb() between checking
++ * @engine->flags and using @engine->ops. Here we change @engine->ops
++ * first, then use smp_wmb() before changing @engine->flags. This ensures
++ * it can check the old flags before using the old ops, or check the old
++ * flags before using the new ops, or check the new flags before using the
++ * new ops, but can never check the new flags before using the old ops.
++ * Hence, utrace_detached_ops might be used with any old flags in place.
++ * It has report_quiesce() and report_reap() callbacks to handle all cases.
++ */
++static void mark_engine_detached(struct utrace_attached_engine *engine)
++{
++ engine->ops = &utrace_detached_ops;
++ smp_wmb();
++ engine->flags = UTRACE_EVENT(QUIESCE);
++}
++
++/*
++ * Get @target to stop and return true if it is already stopped now.
++ * If we return false, it will make some event callback soonish.
++ * Called with @utrace locked.
++ */
++static bool utrace_do_stop(struct task_struct *target, struct utrace *utrace)
++{
++ bool stopped;
++
++ /*
++ * If it will call utrace_report_jctl() but has not gotten
++ * through it yet, then don't consider it quiescent yet.
++ * utrace_report_jctl() will take @utrace->lock and
++ * set @utrace->stopped itself once it finishes. After that,
++ * it is considered quiescent; when it wakes up, it will go
++ * through utrace_get_signal() before doing anything else.
++ */
++ if (task_is_stopped(target) &&
++ !(target->utrace_flags & UTRACE_EVENT(JCTL))) {
++ utrace->stopped = 1;
++ return true;
++ }
++
++ stopped = false;
++ spin_lock_irq(&target->sighand->siglock);
++ if (unlikely(target->exit_state)) {
++ /*
++ * On the exit path, it's only truly quiescent
++ * if it has already been through
++ * utrace_report_death(), or never will.
++ */
++ if (!(target->utrace_flags & DEATH_EVENTS))
++ utrace->stopped = stopped = true;
++ } else if (task_is_stopped(target)) {
++ if (!(target->utrace_flags & UTRACE_EVENT(JCTL)))
++ utrace->stopped = stopped = true;
++ } else if (!utrace->report && !utrace->interrupt) {
++ utrace->report = 1;
++ set_notify_resume(target);
++ }
++ spin_unlock_irq(&target->sighand->siglock);
++
++ return stopped;
++}
++
++/*
++ * If the target is not dead it should not be in tracing
++ * stop any more. Wake it unless it's in job control stop.
++ *
++ * Called with @utrace->lock held and @utrace->stopped set.
++ */
++static void utrace_wakeup(struct task_struct *target, struct utrace *utrace)
++{
++ struct sighand_struct *sighand;
++ unsigned long irqflags;
++
++ utrace->stopped = 0;
++
++ sighand = lock_task_sighand(target, &irqflags);
++ if (unlikely(!sighand))
++ return;
++
++ if (likely(task_is_stopped_or_traced(target))) {
++ if (target->signal->flags & SIGNAL_STOP_STOPPED)
++ target->state = TASK_STOPPED;
++ else
++ wake_up_state(target, __TASK_STOPPED | __TASK_TRACED);
++ }
++
++ unlock_task_sighand(target, &irqflags);
++}
++
++/*
++ * This is called when there might be some detached engines on the list or
++ * some stale bits in @task->utrace_flags. Clean them up and recompute the
++ * flags.
++ *
++ * @wake is false when @task is current. @wake is true when @task is
++ * stopped and @utrace->stopped is set; wake it up if it should not be.
++ *
++ * Called with @utrace->lock held, returns with it released.
++ */
++static void utrace_reset(struct task_struct *task, struct utrace *utrace,
++ bool wake)
++ __releases(utrace->lock)
++{
++ struct utrace_attached_engine *engine, *next;
++ unsigned long flags = 0;
++ LIST_HEAD(detached);
++
++ splice_attaching(utrace);
++
++ /*
++ * Update the set of events of interest from the union
++ * of the interests of the remaining tracing engines.
++ * For any engine marked detached, remove it from the list.
++ * We'll collect them on the detached list.
++ */
++ list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
++ if (engine->ops == &utrace_detached_ops) {
++ engine->ops = NULL;
++ list_move(&engine->entry, &detached);
++ } else {
++ flags |= engine->flags | UTRACE_EVENT(REAP);
++ wake = wake && !engine_wants_stop(engine);
++ }
++ }
++
++ if (task->exit_state) {
++ BUG_ON(utrace->death);
++ flags &= DEAD_FLAGS_MASK;
++ wake = false;
++ } else if (!(flags & UTRACE_EVENT_SYSCALL) &&
++ test_tsk_thread_flag(task, TIF_SYSCALL_TRACE)) {
++ clear_tsk_thread_flag(task, TIF_SYSCALL_TRACE);
++ }
++
++ task->utrace_flags = flags;
++
++ if (wake)
++ utrace_wakeup(task, utrace);
++
++ /*
++ * If any engines are left, we're done.
++ */
++ if (flags) {
++ spin_unlock(&utrace->lock);
++ goto done;
++ }
++
++ /*
++ * No more engines, clear out the utrace. Here we can race with
++ * utrace_release_task(). If it gets task_lock() first, then it
++ * cleans up this struct for us.
++ */
++
++ task_lock(task);
++
++ if (unlikely(task->utrace != utrace)) {
++ task_unlock(task);
++ spin_unlock(&utrace->lock);
++ goto done;
++ }
++
++ rcu_assign_pointer(task->utrace, NULL);
++
++ task_unlock(task);
++
++ rcu_utrace_free(utrace);
++
++done:
++ put_detached_list(&detached);
++}
++
++/**
++ * utrace_control - control a thread being traced by a tracing engine
++ * @target: thread to affect
++ * @engine: attached engine to affect
++ * @action: &enum utrace_resume_action for thread to do
++ *
++ * This is how a tracing engine asks a traced thread to do something.
++ * This call is controlled by the @action argument, which has the
++ * same meaning as the &enum utrace_resume_action value returned by
++ * event reporting callbacks.
++ *
++ * If @target is already dead (@target->exit_state nonzero),
++ * all actions except %UTRACE_DETACH fail with -%ESRCH.
++ *
++ * The following sections describe each option for the @action argument.
++ *
++ * UTRACE_DETACH:
++ *
++ * After this, the @engine data structure is no longer accessible,
++ * and the thread might be reaped. The thread will start running
++ * again if it was stopped and no longer has any attached engines
++ * that want it stopped.
++ *
++ * If the @report_reap callback may already have begun, this fails
++ * with -%ESRCH. If the @report_death callback may already have
++ * begun, this fails with -%EALREADY.
++ *
++ * If @target is not already stopped, then a callback to this engine
++ * might be in progress or about to start on another CPU. If so,
++ * then this returns -%EINPROGRESS; the detach happens as soon as
++ * the pending callback is finished. To synchronize after an
++ * -%EINPROGRESS return, see utrace_barrier().
++ *
++ * If @target is properly stopped before utrace_control() is called,
++ * then after successful return it's guaranteed that no more callbacks
++ * to the @engine->ops vector will be made.
++ *
++ * The only exception is %SIGKILL (and exec or group-exit by another
++ * thread in the group), which can cause asynchronous @report_death
++ * and/or @report_reap callbacks even when %UTRACE_STOP was used.
++ * (In that event, this fails with -%ESRCH or -%EALREADY, see above.)
++ *
++ * UTRACE_STOP:
++ * This asks that @target stop running. This returns 0 only if
++ * @target is already stopped, either for tracing or for job
++ * control. Then @target will remain stopped until another
++ * utrace_control() call is made on @engine; @target can be woken
++ * only by %SIGKILL (or equivalent, such as exec or termination by
++ * another thread in the same thread group).
++ *
++ * This returns -%EINPROGRESS if @target is not already stopped.
++ * Then the effect is like %UTRACE_REPORT. A @report_quiesce or
++ * @report_signal callback will be made soon. Your callback can
++ * then return %UTRACE_STOP to keep @target stopped.
++ *
++ * This does not interrupt system calls in progress, including ones
++ * that sleep for a long time. For that, use %UTRACE_INTERRUPT.
++ * To interrupt system calls and then keep @target stopped, your
++ * @report_signal callback can return %UTRACE_STOP.
++ *
++ * UTRACE_RESUME:
++ *
++ * Just let @target continue running normally, reversing the effect
++ * of a previous %UTRACE_STOP. If another engine is keeping @target
++ * stopped, then it remains stopped until all engines let it resume.
++ * If @target was not stopped, this has no effect.
++ *
++ * UTRACE_REPORT:
++ *
++ * This is like %UTRACE_RESUME, but also ensures that there will be
++ * a @report_quiesce or @report_signal callback made soon. If
++ * @target had been stopped, then there will be a callback before it
++ * resumes running normally. If another engine is keeping @target
++ * stopped, then there might be no callbacks until all engines let
++ * it resume.
++ *
++ * UTRACE_INTERRUPT:
++ *
++ * This is like %UTRACE_REPORT, but ensures that @target will make a
++ * @report_signal callback before it resumes or delivers signals.
++ * If @target was in a system call or about to enter one, work in
++ * progress will be interrupted as if by %SIGSTOP. If another
++ * engine is keeping @target stopped, then there might be no
++ * callbacks until all engines let it resume.
++ *
++ * This gives @engine an opportunity to introduce a forced signal
++ * disposition via its @report_signal callback.
++ *
++ * UTRACE_SINGLESTEP:
++ *
++ * It's invalid to use this unless arch_has_single_step() returned true.
++ * This is like %UTRACE_RESUME, but resumes for one user instruction
++ * only. It's invalid to use this in utrace_control() unless @target
++ * had been stopped by @engine previously.
++ *
++ * Note that passing %UTRACE_SINGLESTEP or %UTRACE_BLOCKSTEP to
++ * utrace_control() or returning it from an event callback alone does
++ * not necessarily ensure that stepping will be enabled. If there are
++ * more callbacks made to any engine before returning to user mode,
++ * then the resume action is chosen only by the last set of callbacks.
++ * To be sure, enable %UTRACE_EVENT(%QUIESCE) and look for the
++ * @report_quiesce callback with a zero event mask, or the
++ * @report_signal callback with %UTRACE_SIGNAL_REPORT.
++ *
++ * UTRACE_BLOCKSTEP:
++ *
++ * It's invalid to use this unless arch_has_block_step() returned true.
++ * This is like %UTRACE_SINGLESTEP, but resumes for one whole basic
++ * block of user instructions.
++ *
++ * %UTRACE_BLOCKSTEP devolves to %UTRACE_SINGLESTEP when another
++ * tracing engine is using %UTRACE_SINGLESTEP at the same time.
++ */
++int utrace_control(struct task_struct *target,
++ struct utrace_attached_engine *engine,
++ enum utrace_resume_action action)
++{
++ struct utrace *utrace;
++ bool resume;
++ int ret;
++
++ if (unlikely(action > UTRACE_DETACH))
++ return -EINVAL;
++
++ utrace = get_utrace_lock(target, engine, true);
++ if (unlikely(IS_ERR(utrace)))
++ return PTR_ERR(utrace);
++
++ if (target->exit_state) {
++ /*
++ * You can't do anything to a dead task but detach it.
++ * If release_task() has been called, you can't do that.
++ *
++ * On the exit path, DEATH and QUIESCE event bits are
++ * set only before utrace_report_death() has taken the
++ * lock. At that point, the death report will come
++ * soon, so disallow detach until it's done. This
++ * prevents us from racing with it detaching itself.
++ */
++ if (action != UTRACE_DETACH ||
++ unlikely(utrace->reap)) {
++ spin_unlock(&utrace->lock);
++ return -ESRCH;
++ } else if (unlikely(target->utrace_flags & DEATH_EVENTS) ||
++ unlikely(utrace->death)) {
++ /*
++ * We have already started the death report, or
++ * are about to very soon. We can't prevent
++ * the report_death and report_reap callbacks,
++ * so tell the caller they will happen.
++ */
++ spin_unlock(&utrace->lock);
++ return -EALREADY;
++ }
++ }
++
++ resume = utrace->stopped;
++ ret = 0;
++
++ clear_engine_wants_stop(engine);
++ switch (action) {
++ case UTRACE_STOP:
++ mark_engine_wants_stop(engine);
++ if (!resume && !utrace_do_stop(target, utrace))
++ ret = -EINPROGRESS;
++ resume = false;
++ break;
++
++ case UTRACE_DETACH:
++ mark_engine_detached(engine);
++ resume = resume || utrace_do_stop(target, utrace);
++ if (!resume) {
++ smp_mb();
++ if (utrace->reporting == engine)
++ ret = -EINPROGRESS;
++ break;
++ }
++ /* Fall through. */
++
++ case UTRACE_RESUME:
++ /*
++ * This and all other cases imply resuming if stopped.
++ * There might not be another report before it just
++ * resumes, so make sure single-step is not left set.
++ */
++ if (likely(resume))
++ user_disable_single_step(target);
++ break;
++
++ case UTRACE_REPORT:
++ /*
++ * Make the thread call tracehook_notify_resume() soon.
++ * But don't bother if it's already been stopped or
++ * interrupted. In those cases, utrace_get_signal()
++ * will be reporting soon.
++ */
++ if (!utrace->report && !utrace->interrupt && !utrace->stopped) {
++ utrace->report = 1;
++ set_notify_resume(target);
++ }
++ break;
++
++ case UTRACE_INTERRUPT:
++ /*
++ * Make the thread call tracehook_get_signal() soon.
++ */
++ if (utrace->interrupt)
++ break;
++ utrace->interrupt = 1;
++
++ /*
++ * If it's not already stopped, interrupt it now.
++ * We need the siglock here in case it calls
++ * recalc_sigpending() and clears its own
++ * TIF_SIGPENDING. By taking the lock, we've
++ * serialized any later recalc_sigpending() after
++ * our setting of utrace->interrupt to force it on.
++ */
++ if (resume) {
++ /*
++ * This is really just to keep the invariant
++ * that TIF_SIGPENDING is set with utrace->interrupt.
++ * When it's stopped, we know it's always going
++ * through utrace_get_signal and will recalculate.
++ */
++ set_tsk_thread_flag(target, TIF_SIGPENDING);
++ } else {
++ struct sighand_struct *sighand;
++ unsigned long irqflags;
++ sighand = lock_task_sighand(target, &irqflags);
++ if (likely(sighand)) {
++ signal_wake_up(target, 0);
++ unlock_task_sighand(target, &irqflags);
++ }
++ }
++ break;
++
++ case UTRACE_BLOCKSTEP:
++ /*
++ * Resume from stopped, step one block.
++ */
++ if (unlikely(!arch_has_block_step())) {
++ WARN_ON(1);
++ /* Fall through to treat it as SINGLESTEP. */
++ } else if (likely(resume)) {
++ user_enable_block_step(target);
++ break;
++ }
++
++ case UTRACE_SINGLESTEP:
++ /*
++ * Resume from stopped, step one instruction.
++ */
++ if (unlikely(!arch_has_single_step())) {
++ WARN_ON(1);
++ resume = false;
++ ret = -EOPNOTSUPP;
++ break;
++ }
++
++ if (likely(resume))
++ user_enable_single_step(target);
++ else
++ /*
++ * You were supposed to stop it before asking
++ * it to step.
++ */
++ ret = -EAGAIN;
++ break;
++ }
++
++ /*
++ * Let the thread resume running. If it's not stopped now,
++ * there is nothing more we need to do.
++ */
++ if (resume)
++ utrace_reset(target, utrace, true);
++ else
++ spin_unlock(&utrace->lock);
++
++ return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_control);
++
++/**
++ * utrace_barrier - synchronize with simultaneous tracing callbacks
++ * @target: thread to affect
++ * @engine: engine to affect (can be detached)
++ *
++ * This blocks while @target might be in the midst of making a callback to
++ * @engine. It can be interrupted by signals and will return -%ERESTARTSYS.
++ * A return value of zero means no callback from @target to @engine was
++ * in progress.
++ *
++ * It's not necessary to keep the @target pointer alive for this call.
++ * It's only necessary to hold a ref on @engine. This will return
++ * safely even if @target has been reaped and has no task refs.
++ *
++ * A successful return from utrace_barrier() guarantees its ordering
++ * with respect to utrace_set_events() and utrace_control() calls. If
++ * @target was not properly stopped, event callbacks just disabled might
++ * still be in progress; utrace_barrier() waits until there is no chance
++ * an unwanted callback can be in progress.
++ */
++int utrace_barrier(struct task_struct *target,
++ struct utrace_attached_engine *engine)
++{
++ struct utrace *utrace;
++ int ret = -ERESTARTSYS;
++
++ if (unlikely(target == current))
++ return 0;
++
++ do {
++ utrace = get_utrace_lock(target, engine, false);
++ if (unlikely(IS_ERR(utrace))) {
++ ret = PTR_ERR(utrace);
++ if (ret != -ERESTARTSYS)
++ break;
++ } else {
++ if (utrace->stopped || utrace->reporting != engine)
++ ret = 0;
++ spin_unlock(&utrace->lock);
++ if (!ret)
++ break;
++ }
++ schedule_timeout_interruptible(1);
++ } while (!signal_pending(current));
++
++ return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_barrier);
++
++/*
++ * This is local state used for reporting loops, perhaps optimized away.
++ */
++struct utrace_report {
++ enum utrace_resume_action action;
++ u32 result;
++ bool detaches;
++ bool takers;
++ bool killed;
++};
++
++#define INIT_REPORT(var) \
++ struct utrace_report var = { UTRACE_RESUME, 0, false, false, false }
++
++/*
++ * We are now making the report, so clear the flag saying we need one.
++ */
++static void start_report(struct utrace *utrace)
++{
++ BUG_ON(utrace->stopped);
++ if (utrace->report) {
++ spin_lock(&utrace->lock);
++ utrace->report = 0;
++ splice_attaching(utrace);
++ spin_unlock(&utrace->lock);
++ }
++}
++
++/*
++ * Complete a normal reporting pass, pairing with a start_report() call.
++ * This handles any UTRACE_DETACH or UTRACE_REPORT or UTRACE_INTERRUPT
++ * returns from engine callbacks. If any engine's last callback used
++ * UTRACE_STOP, we do UTRACE_REPORT here to ensure we stop before user
++ * mode. If there were no callbacks made, it will recompute
++ * @task->utrace_flags to avoid another false-positive.
++ */
++static void finish_report(struct utrace_report *report,
++ struct task_struct *task, struct utrace *utrace)
++{
++ bool clean = (report->takers && !report->detaches);
++
++ if (report->action <= UTRACE_REPORT && !utrace->report) {
++ spin_lock(&utrace->lock);
++ utrace->report = 1;
++ set_tsk_thread_flag(task, TIF_NOTIFY_RESUME);
++ } else if (report->action == UTRACE_INTERRUPT && !utrace->interrupt) {
++ spin_lock(&utrace->lock);
++ utrace->interrupt = 1;
++ set_tsk_thread_flag(task, TIF_SIGPENDING);
++ } else if (clean) {
++ return;
++ } else {
++ spin_lock(&utrace->lock);
++ }
++
++ if (clean)
++ spin_unlock(&utrace->lock);
++ else
++ utrace_reset(task, utrace, false);
++}
++
++/*
++ * Apply the return value of one engine callback to @report.
++ * Returns true if @engine detached and should not get any more callbacks.
++ */
++static bool finish_callback(struct utrace *utrace,
++ struct utrace_report *report,
++ struct utrace_attached_engine *engine,
++ u32 ret)
++{
++ enum utrace_resume_action action = utrace_resume_action(ret);
++
++ utrace->reporting = NULL;
++
++ /*
++ * This is a good place to make sure tracing engines don't
++ * introduce too much latency under voluntary preemption.
++ */
++ if (need_resched())
++ cond_resched();
++
++ report->result = ret & ~UTRACE_RESUME_MASK;
++
++ /*
++ * If utrace_control() was used, treat that like UTRACE_DETACH here.
++ */
++ if (action == UTRACE_DETACH || engine->ops == &utrace_detached_ops) {
++ engine->ops = &utrace_detached_ops;
++ report->detaches = true;
++ return true;
++ }
++
++ if (action < report->action)
++ report->action = action;
++
++ if (action == UTRACE_STOP) {
++ if (!engine_wants_stop(engine)) {
++ spin_lock(&utrace->lock);
++ mark_engine_wants_stop(engine);
++ spin_unlock(&utrace->lock);
++ }
++ } else if (engine_wants_stop(engine)) {
++ spin_lock(&utrace->lock);
++ clear_engine_wants_stop(engine);
++ spin_unlock(&utrace->lock);
++ }
++
++ return false;
++}
++
++/*
++ * Start the callbacks for @engine to consider @event (a bit mask).
++ * This makes the report_quiesce() callback first. If @engine wants
++ * a specific callback for @event, we return the ops vector to use.
++ * If not, we return NULL. The return value from the ops->callback
++ * function called should be passed to finish_callback().
++ */
++static const struct utrace_engine_ops *start_callback(
++ struct utrace *utrace, struct utrace_report *report,
++ struct utrace_attached_engine *engine, struct task_struct *task,
++ unsigned long event)
++{
++ const struct utrace_engine_ops *ops;
++ unsigned long want;
++
++ utrace->reporting = engine;
++ smp_mb();
++
++ /*
++ * This pairs with the barrier in mark_engine_detached().
++ * It makes sure that we never see the old ops vector with
++ * the new flags, in case the original vector had no report_quiesce.
++ */
++ want = engine->flags;
++ smp_rmb();
++ ops = engine->ops;
++
++ if (want & UTRACE_EVENT(QUIESCE)) {
++ if (finish_callback(utrace, report, engine,
++ (*ops->report_quiesce)(report->action,
++ engine, task,
++ event)))
++ goto nocall;
++
++ utrace->reporting = engine;
++ smp_mb();
++ want = engine->flags;
++ }
++
++ if (want & ENGINE_STOP)
++ report->action = UTRACE_STOP;
++
++ if (want & event) {
++ report->takers = true;
++ return ops;
++ }
++
++nocall:
++ utrace->reporting = NULL;
++ return NULL;
++}
++
++/*
++ * Do a normal reporting pass for engines interested in @event.
++ * @callback is the name of the member in the ops vector, and remaining
++ * args are the extras it takes after the standard three args.
++ */
++#define REPORT(task, utrace, report, event, callback, ...) \
++ do { \
++ start_report(utrace); \
++ REPORT_CALLBACKS(task, utrace, report, event, callback, \
++ (report)->action, engine, current, \
++ ## __VA_ARGS__); \
++ finish_report(report, task, utrace); \
++ } while (0)
++#define REPORT_CALLBACKS(task, utrace, report, event, callback, ...) \
++ do { \
++ struct utrace_attached_engine *engine, *next; \
++ const struct utrace_engine_ops *ops; \
++ list_for_each_entry_safe(engine, next, \
++ &utrace->attached, entry) { \
++ ops = start_callback(utrace, report, engine, task, \
++ event); \
++ if (!ops) \
++ continue; \
++ finish_callback(utrace, report, engine, \
++ (*ops->callback)(__VA_ARGS__)); \
++ } \
++ } while (0)
++
++/*
++ * Called iff UTRACE_EVENT(EXEC) flag is set.
++ */
++void utrace_report_exec(struct linux_binfmt *fmt, struct linux_binprm *bprm,
++ struct pt_regs *regs)
++{
++ struct task_struct *task = current;
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++
++ REPORT(task, utrace, &report, UTRACE_EVENT(EXEC),
++ report_exec, fmt, bprm, regs);
++}
++
++/*
++ * Called iff UTRACE_EVENT(SYSCALL_ENTRY) flag is set.
++ * Return true to prevent the system call.
++ */
++bool utrace_report_syscall_entry(struct pt_regs *regs)
++{
++ struct task_struct *task = current;
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++
++ start_report(utrace);
++ REPORT_CALLBACKS(task, utrace, &report, UTRACE_EVENT(SYSCALL_ENTRY),
++ report_syscall_entry, report.result | report.action,
++ engine, current, regs);
++ finish_report(&report, task, utrace);
++
++ if (report.action == UTRACE_STOP && unlikely(utrace_stop(task, utrace)))
++ /*
++ * We are continuing despite UTRACE_STOP because of a
++ * SIGKILL. Don't let the system call actually proceed.
++ */
++ return true;
++
++ if (unlikely(report.result == UTRACE_SYSCALL_ABORT))
++ return true;
++
++ if (signal_pending(task)) {
++ /*
++ * Clear TIF_SIGPENDING if it no longer needs to be set.
++ * It may have been set as part of quiescence, and won't
++ * ever have been cleared by another thread. For other
++ * reports, we can just leave it set and will go through
++ * utrace_get_signal() to reset things. But here we are
++ * about to enter a syscall, which might bail out with an
++ * -ERESTART* error if it's set now.
++ */
++ spin_lock_irq(&task->sighand->siglock);
++ recalc_sigpending();
++ spin_unlock_irq(&task->sighand->siglock);
++ }
++
++ return false;
++}
++
++/*
++ * Called iff UTRACE_EVENT(SYSCALL_EXIT) flag is set.
++ */
++void utrace_report_syscall_exit(struct pt_regs *regs)
++{
++ struct task_struct *task = current;
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++
++ REPORT(task, utrace, &report, UTRACE_EVENT(SYSCALL_EXIT),
++ report_syscall_exit, regs);
++}
++
++/*
++ * Called iff UTRACE_EVENT(CLONE) flag is set.
++ * This notification call blocks the wake_up_new_task call on the child.
++ * So we must not quiesce here. tracehook_report_clone_complete will do
++ * a quiescence check momentarily.
++ */
++void utrace_report_clone(unsigned long clone_flags, struct task_struct *child)
++{
++ struct task_struct *task = current;
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++
++ utrace->u.live.cloning = child;
++
++ REPORT(task, utrace, &report, UTRACE_EVENT(CLONE),
++ report_clone, clone_flags, child);
++
++ utrace->u.live.cloning = NULL;
++}
++
++/*
++ * Called iff UTRACE_EVENT(JCTL) flag is set.
++ */
++void utrace_report_jctl(int notify, int what)
++{
++ struct task_struct *task = current;
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++ bool was_stopped = task_is_stopped(task);
++
++ /*
++ * We get here with CLD_STOPPED when we've just entered
++ * TASK_STOPPED, or with CLD_CONTINUED when we've just come
++ * out but not yet been through utrace_get_signal() again.
++ *
++ * While in TASK_STOPPED, we can be considered safely
++ * stopped by utrace_do_stop() and detached asynchronously.
++ * If we woke up and checked task->utrace_flags before that
++ * was finished, we might be here with utrace already
++ * removed or in the middle of being removed.
++ *
++ * RCU makes it safe to get the utrace->lock even if it's
++ * being freed. Once we have that lock, either an external
++ * detach has finished and this struct has been freed, or
++ * else we know we are excluding any other detach attempt.
++ *
++ * If we are indeed attached, then make sure we are no
++ * longer considered stopped while we run callbacks.
++ */
++ rcu_read_lock();
++ utrace = rcu_dereference(task->utrace);
++ if (unlikely(!utrace)) {
++ rcu_read_unlock();
++ return;
++ }
++ spin_lock(&utrace->lock);
++ utrace->stopped = 0;
++ utrace->report = 0;
++ spin_unlock(&utrace->lock);
++ rcu_read_unlock();
++
++ REPORT(task, utrace, &report, UTRACE_EVENT(JCTL),
++ report_jctl, was_stopped ? CLD_STOPPED : CLD_CONTINUED, what);
++
++ if (was_stopped && !task_is_stopped(task)) {
++ /*
++ * The event report hooks could have blocked, though
++ * it should have been briefly. Make sure we're in
++ * TASK_STOPPED state again to block properly, unless
++ * we've just come back out of job control stop.
++ */
++ spin_lock_irq(&task->sighand->siglock);
++ if (task->signal->flags & SIGNAL_STOP_STOPPED)
++ __set_current_state(TASK_STOPPED);
++ spin_unlock_irq(&task->sighand->siglock);
++ }
++
++ if (task_is_stopped(current)) {
++ /*
++ * While in TASK_STOPPED, we can be considered safely
++ * stopped by utrace_do_stop() only once we set this.
++ */
++ spin_lock(&utrace->lock);
++ utrace->stopped = 1;
++ spin_unlock(&utrace->lock);
++ }
++}
++
++/*
++ * Called iff UTRACE_EVENT(EXIT) flag is set.
++ */
++void utrace_report_exit(long *exit_code)
++{
++ struct task_struct *task = current;
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++ long orig_code = *exit_code;
++
++ REPORT(task, utrace, &report, UTRACE_EVENT(EXIT),
++ report_exit, orig_code, exit_code);
++
++ if (report.action == UTRACE_STOP)
++ utrace_stop(task, utrace);
++}
++
++/*
++ * Called iff UTRACE_EVENT(DEATH) or UTRACE_EVENT(QUIESCE) flag is set.
++ *
++ * It is always possible that we are racing with utrace_release_task here.
++ * For this reason, utrace_release_task checks for the event bits that get
++ * us here, and delays its cleanup for us to do.
++ */
++void utrace_report_death(struct task_struct *task, struct utrace *utrace,
++ bool group_dead, int signal)
++{
++ INIT_REPORT(report);
++
++ BUG_ON(!task->exit_state);
++
++ /*
++ * We are presently considered "quiescent"--which is accurate
++ * inasmuch as we won't run any more user instructions ever again.
++ * But for utrace_control and utrace_set_events to be robust, they
++ * must be sure whether or not we will run any more callbacks. If
++ * a call comes in before we do, taking the lock here synchronizes
++ * us so we don't run any callbacks just disabled. Calls that come
++ * in while we're running the callbacks will see the exit.death
++ * flag and know that we are not yet fully quiescent for purposes
++ * of detach bookkeeping.
++ */
++ spin_lock(&utrace->lock);
++ BUG_ON(utrace->death);
++ utrace->death = 1;
++ utrace->report = 0;
++ utrace->interrupt = 0;
++ spin_unlock(&utrace->lock);
++
++ REPORT_CALLBACKS(task, utrace, &report, UTRACE_EVENT(DEATH),
++ report_death, engine, task, group_dead, signal);
++
++ spin_lock(&utrace->lock);
++
++ /*
++ * After we unlock (possibly inside utrace_reap for callbacks) with
++ * this flag clear, competing utrace_control/utrace_set_events calls
++ * know that we've finished our callbacks and any detach bookkeeping.
++ */
++ utrace->death = 0;
++
++ if (utrace->reap)
++ /*
++ * utrace_release_task() was already called in parallel.
++ * We must complete its work now.
++ */
++ utrace_reap(task, utrace);
++ else
++ utrace_reset(task, utrace, false);
++}
++
++/*
++ * Finish the last reporting pass before returning to user mode.
++ *
++ * Returns true if we might have been in TASK_TRACED and then resumed.
++ * In that event, signal_pending() might not be set when it should be,
++ * as the signals code passes us over while we're in TASK_TRACED.
++ */
++static bool finish_resume_report(struct utrace_report *report,
++ struct task_struct *task,
++ struct utrace *utrace)
++{
++ if (report->detaches || !report->takers) {
++ spin_lock(&utrace->lock);
++ utrace_reset(task, utrace, false);
++ }
++
++ switch (report->action) {
++ case UTRACE_INTERRUPT:
++ if (!signal_pending(task))
++ set_tsk_thread_flag(task, TIF_SIGPENDING);
++ break;
++
++ case UTRACE_SINGLESTEP:
++ user_enable_single_step(task);
++ break;
++
++ case UTRACE_BLOCKSTEP:
++ user_enable_block_step(task);
++ break;
++
++ case UTRACE_STOP:
++ report->killed = utrace_stop(task, utrace);
++ return likely(!report->killed);
++
++ case UTRACE_REPORT:
++ case UTRACE_RESUME:
++ default:
++ user_disable_single_step(task);
++ break;
++ }
++
++ return false;
++}
++
++/*
++ * This is called when TIF_NOTIFY_RESUME had been set (and is now clear).
++ * We are close to user mode, and this is the place to report or stop.
++ * When we return, we're going to user mode or into the signals code.
++ */
++void utrace_resume(struct task_struct *task, struct pt_regs *regs)
++{
++ struct utrace *utrace = task->utrace;
++ INIT_REPORT(report);
++ struct utrace_attached_engine *engine, *next;
++
++ /*
++ * Some machines get here with interrupts disabled. The same arch
++ * code path leads to calling into get_signal_to_deliver(), which
++ * implicitly reenables them by virtue of spin_unlock_irq.
++ */
++ local_irq_enable();
++
++ /*
++ * If this flag is still set it's because there was a signal
++ * handler setup done but no report_signal following it. Clear
++ * the flag before we get to user so it doesn't confuse us later.
++ */
++ if (unlikely(utrace->signal_handler)) {
++ int skip;
++ spin_lock(&utrace->lock);
++ utrace->signal_handler = 0;
++ skip = !utrace->report;
++ spin_unlock(&utrace->lock);
++ if (skip)
++ return;
++ }
++
++ /*
++ * If UTRACE_INTERRUPT was just used, we don't bother with a
++ * report here. We will report and stop in utrace_get_signal().
++ */
++ if (unlikely(utrace->interrupt)) {
++ BUG_ON(!signal_pending(task));
++ return;
++ }
++
++ /*
++ * Do a simple reporting pass, with no callback after report_quiesce.
++ */
++ start_report(utrace);
++
++ list_for_each_entry_safe(engine, next, &utrace->attached, entry)
++ start_callback(utrace, &report, engine, task, 0);
++
++ /*
++ * Finish the report and either stop or get ready to resume.
++ * If we stop and then signal_pending() is clear, we
++ * should recompute it before returning to user mode.
++ */
++ if (finish_resume_report(&report, task, utrace) &&
++ !signal_pending(task)) {
++ spin_lock_irq(&task->sighand->siglock);
++ recalc_sigpending();
++ spin_unlock_irq(&task->sighand->siglock);
++ }
++}
++
++/*
++ * Return true if current has forced signal_pending().
++ *
++ * This is called only when current->utrace_flags is nonzero, so we know
++ * that current->utrace must be set. It's not inlined in tracehook.h
++ * just so that struct utrace can stay opaque outside this file.
++ */
++bool utrace_interrupt_pending(void)
++{
++ return current->utrace->interrupt;
++}
++
++/*
++ * Take the siglock and push @info back on our queue.
++ * Returns with @task->sighand->siglock held.
++ */
++static void push_back_signal(struct task_struct *task, siginfo_t *info)
++ __acquires(task->sighand->siglock)
++{
++ struct sigqueue *q;
++
++ if (unlikely(!info->si_signo)) { /* Oh, a wise guy! */
++ spin_lock_irq(&task->sighand->siglock);
++ return;
++ }
++
++ q = sigqueue_alloc();
++ if (likely(q)) {
++ q->flags = 0;
++ copy_siginfo(&q->info, info);
++ }
++
++ spin_lock_irq(&task->sighand->siglock);
++
++ sigaddset(&task->pending.signal, info->si_signo);
++ if (likely(q))
++ list_add(&q->list, &task->pending.list);
++
++ set_tsk_thread_flag(task, TIF_SIGPENDING);
++}
++
++/*
++ * This is the hook from the signals code, called with the siglock held.
++ * Here is the ideal place to stop. We also dequeue and intercept signals.
++ */
++int utrace_get_signal(struct task_struct *task, struct pt_regs *regs,
++ siginfo_t *info, struct k_sigaction *return_ka)
++ __releases(task->sighand->siglock)
++ __acquires(task->sighand->siglock)
++{
++ struct utrace *utrace;
++ struct k_sigaction *ka;
++ INIT_REPORT(report);
++ struct utrace_attached_engine *engine, *next;
++ const struct utrace_engine_ops *ops;
++ unsigned long event, want;
++ u32 ret;
++ int signr;
++
++ /*
++ * We could have been considered quiescent while we were in
++ * TASK_STOPPED, and detached asynchronously. If we woke up
++ * and checked task->utrace_flags before that was finished,
++ * we might be here with utrace already removed or in the
++ * middle of being removed.
++ */
++ rcu_read_lock();
++ utrace = rcu_dereference(task->utrace);
++ if (unlikely(utrace == NULL)) {
++ rcu_read_unlock();
++ return 0;
++ }
++
++ if (utrace->interrupt || utrace->report || utrace->signal_handler) {
++ /*
++ * We've been asked for an explicit report before we
++ * even check for pending signals.
++ */
++
++ spin_unlock_irq(&task->sighand->siglock);
++
++ /*
++ * RCU makes it safe to get the utrace->lock even if
++ * it's being freed. Once we have that lock, either an
++ * external detach has finished and this struct has been
++ * freed, or else we know we are excluding any other
++ * detach attempt.
++ */
++ spin_lock(&utrace->lock);
++ rcu_read_unlock();
++
++ if (unlikely(task->utrace != utrace)) {
++ spin_unlock(&utrace->lock);
++ cond_resched();
++ return -1;
++ }
++
++ splice_attaching(utrace);
++
++ if (unlikely(!utrace->interrupt) && unlikely(!utrace->report))
++ report.result = UTRACE_SIGNAL_IGN;
++ else if (utrace->signal_handler)
++ report.result = UTRACE_SIGNAL_HANDLER;
++ else
++ report.result = UTRACE_SIGNAL_REPORT;
++
++ /*
++ * We are now making the report and it's on the
++ * interrupt path, so clear the flags asking for those.
++ */
++ utrace->interrupt = utrace->report = utrace->signal_handler = 0;
++
++ /*
++ * Make sure signal_pending() only returns true
++ * if there are real signals pending.
++ */
++ if (signal_pending(task)) {
++ spin_lock_irq(&task->sighand->siglock);
++ recalc_sigpending();
++ spin_unlock_irq(&task->sighand->siglock);
++ }
++
++ spin_unlock(&utrace->lock);
++
++ if (unlikely(report.result == UTRACE_SIGNAL_IGN))
++ /*
++ * We only got here to clear utrace->signal_handler.
++ */
++ return -1;
++
++ /*
++ * Do a reporting pass for no signal, just for EVENT(QUIESCE).
++ * The engine callbacks can fill in *info and *return_ka.
++ * We'll pass NULL for the @orig_ka argument to indicate
++ * that there was no original signal.
++ */
++ event = 0;
++ ka = NULL;
++ memset(return_ka, 0, sizeof *return_ka);
++ } else if ((task->utrace_flags & UTRACE_EVENT_SIGNAL_ALL) == 0) {
++ /*
++ * If noone is interested in intercepting signals,
++ * let the caller just dequeue them normally.
++ */
++ rcu_read_unlock();
++ return 0;
++ } else {
++ if (unlikely(utrace->stopped)) {
++ /*
++ * We were just in TASK_STOPPED, so we have to
++ * check for the race mentioned above.
++ *
++ * RCU makes it safe to get the utrace->lock even
++ * if it's being freed. Once we have that lock,
++ * either an external detach has finished and this
++ * struct has been freed, or else we know we are
++ * excluding any other detach attempt. Since we
++ * are no longer in TASK_STOPPED now, all we needed
++ * the lock for was to order any utrace_do_stop()
++ * call after us.
++ */
++ spin_unlock_irq(&task->sighand->siglock);
++ spin_lock(&utrace->lock);
++ rcu_read_unlock();
++ if (unlikely(task->utrace != utrace)) {
++ spin_unlock(&utrace->lock);
++ cond_resched();
++ return -1;
++ }
++ utrace->stopped = 0;
++ spin_unlock(&utrace->lock);
++ spin_lock_irq(&task->sighand->siglock);
++ } else {
++ rcu_read_unlock();
++ }
++
++ /*
++ * Steal the next signal so we can let tracing engines
++ * examine it. From the signal number and sigaction,
++ * determine what normal delivery would do. If no
++ * engine perturbs it, we'll do that by returning the
++ * signal number after setting *return_ka.
++ */
++ signr = dequeue_signal(task, &task->blocked, info);
++ if (signr == 0)
++ return signr;
++ BUG_ON(signr != info->si_signo);
++
++ ka = &task->sighand->action[signr - 1];
++ *return_ka = *ka;
++
++ /*
++ * We are never allowed to interfere with SIGKILL.
++ * Just punt after filling in *return_ka for our caller.
++ */
++ if (signr == SIGKILL)
++ return signr;
++
++ if (ka->sa.sa_handler == SIG_IGN) {
++ event = UTRACE_EVENT(SIGNAL_IGN);
++ report.result = UTRACE_SIGNAL_IGN;
++ } else if (ka->sa.sa_handler != SIG_DFL) {
++ event = UTRACE_EVENT(SIGNAL);
++ report.result = UTRACE_SIGNAL_DELIVER;
++ } else if (sig_kernel_coredump(signr)) {
++ event = UTRACE_EVENT(SIGNAL_CORE);
++ report.result = UTRACE_SIGNAL_CORE;
++ } else if (sig_kernel_ignore(signr)) {
++ event = UTRACE_EVENT(SIGNAL_IGN);
++ report.result = UTRACE_SIGNAL_IGN;
++ } else if (signr == SIGSTOP) {
++ event = UTRACE_EVENT(SIGNAL_STOP);
++ report.result = UTRACE_SIGNAL_STOP;
++ } else if (sig_kernel_stop(signr)) {
++ event = UTRACE_EVENT(SIGNAL_STOP);
++ report.result = UTRACE_SIGNAL_TSTP;
++ } else {
++ event = UTRACE_EVENT(SIGNAL_TERM);
++ report.result = UTRACE_SIGNAL_TERM;
++ }
++
++ /*
++ * Now that we know what event type this signal is,
++ * we can short-circuit if noone cares about those.
++ */
++ if ((task->utrace_flags & (event | UTRACE_EVENT(QUIESCE))) == 0)
++ return signr;
++
++ /*
++ * We have some interested engines, so tell them about
++ * the signal and let them change its disposition.
++ */
++ spin_unlock_irq(&task->sighand->siglock);
++ }
++
++ /*
++ * This reporting pass chooses what signal disposition we'll act on.
++ */
++ list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
++ utrace->reporting = engine;
++ smp_mb();
++
++ /*
++ * This pairs with the barrier in mark_engine_detached(),
++ * see start_callback() comments.
++ */
++ want = engine->flags;
++ smp_rmb();
++ ops = engine->ops;
++
++ if ((want & (event | UTRACE_EVENT(QUIESCE))) == 0) {
++ utrace->reporting = NULL;
++ continue;
++ }
++
++ if (ops->report_signal)
++ ret = (*ops->report_signal)(
++ report.result | report.action, engine, task,
++ regs, info, ka, return_ka);
++ else
++ ret = (report.result | (*ops->report_quiesce)(
++ report.action, engine, task, event));
++
++ /*
++ * Avoid a tight loop reporting again and again if some
++ * engine is too stupid.
++ */
++ switch (utrace_resume_action(ret)) {
++ default:
++ break;
++ case UTRACE_INTERRUPT:
++ case UTRACE_REPORT:
++ ret = (ret & ~UTRACE_RESUME_MASK) | UTRACE_RESUME;
++ break;
++ }
++
++ finish_callback(utrace, &report, engine, ret);
++ }
++
++ /*
++ * We express the chosen action to the signals code in terms
++ * of a representative signal whose default action does it.
++ * Our caller uses our return value (signr) to decide what to
++ * do, but uses info->si_signo as the signal number to report.
++ */
++ switch (utrace_signal_action(report.result)) {
++ case UTRACE_SIGNAL_TERM:
++ signr = SIGTERM;
++ break;
++
++ case UTRACE_SIGNAL_CORE:
++ signr = SIGQUIT;
++ break;
++
++ case UTRACE_SIGNAL_STOP:
++ signr = SIGSTOP;
++ break;
++
++ case UTRACE_SIGNAL_TSTP:
++ signr = SIGTSTP;
++ break;
++
++ case UTRACE_SIGNAL_DELIVER:
++ signr = info->si_signo;
++
++ if (return_ka->sa.sa_handler == SIG_DFL) {
++ /*
++ * We'll do signr's normal default action.
++ * For ignore, we'll fall through below.
++ * For stop/death, break locks and returns it.
++ */
++ if (likely(signr) && !sig_kernel_ignore(signr))
++ break;
++ } else if (return_ka->sa.sa_handler != SIG_IGN &&
++ likely(signr)) {
++ /*
++ * The handler will run. If an engine wanted to
++ * stop or step, then make sure we do another
++ * report after signal handler setup.
++ */
++ if (report.action != UTRACE_RESUME) {
++ spin_lock(&utrace->lock);
++ utrace->interrupt = 1;
++ spin_unlock(&utrace->lock);
++ set_tsk_thread_flag(task, TIF_SIGPENDING);
++ }
++
++ if (unlikely(report.result & UTRACE_SIGNAL_HOLD))
++ push_back_signal(task, info);
++ else
++ spin_lock_irq(&task->sighand->siglock);
++
++ /*
++ * We do the SA_ONESHOT work here since the
++ * normal path will only touch *return_ka now.
++ */
++ if (unlikely(return_ka->sa.sa_flags & SA_ONESHOT)) {
++ return_ka->sa.sa_flags &= ~SA_ONESHOT;
++ if (likely(valid_signal(signr))) {
++ ka = &task->sighand->action[signr - 1];
++ ka->sa.sa_handler = SIG_DFL;
++ }
++ }
++
++ return signr;
++ }
++
++ /* Fall through for an ignored signal. */
++
++ case UTRACE_SIGNAL_IGN:
++ case UTRACE_SIGNAL_REPORT:
++ default:
++ /*
++ * If the signal is being ignored, then we are on the way
++ * directly back to user mode. We can stop here, or step,
++ * as in utrace_resume(), above. After we've dealt with that,
++ * our caller will relock and come back through here.
++ */
++ finish_resume_report(&report, task, utrace);
++
++ if (unlikely(report.killed)) {
++ /*
++ * The only reason we woke up now was because of a
++ * SIGKILL. Don't do normal dequeuing in case it
++ * might get a signal other than SIGKILL. That would
++ * perturb the death state so it might differ from
++ * what the debugger would have allowed to happen.
++ * Instead, pluck out just the SIGKILL to be sure
++ * we'll die immediately with nothing else different
++ * from the quiescent state the debugger wanted us in.
++ */
++ sigset_t sigkill_only;
++ siginitsetinv(&sigkill_only, sigmask(SIGKILL));
++ spin_lock_irq(&task->sighand->siglock);
++ signr = dequeue_signal(task, &sigkill_only, info);
++ BUG_ON(signr != SIGKILL);
++ *return_ka = task->sighand->action[SIGKILL - 1];
++ return signr;
++ }
++
++ if (unlikely(report.result & UTRACE_SIGNAL_HOLD)) {
++ push_back_signal(task, info);
++ spin_unlock_irq(&task->sighand->siglock);
++ }
++
++ return -1;
++ }
++
++ return_ka->sa.sa_handler = SIG_DFL;
++
++ if (unlikely(report.result & UTRACE_SIGNAL_HOLD))
++ push_back_signal(task, info);
++ else
++ spin_lock_irq(&task->sighand->siglock);
++
++ if (sig_kernel_stop(signr))
++ task->signal->flags |= SIGNAL_STOP_DEQUEUED;
++
++ return signr;
++}
++
++/*
++ * This gets called after a signal handler has been set up.
++ * We set a flag so the next report knows it happened.
++ * If we're already stepping, make sure we do a report_signal.
++ * If not, make sure we get into utrace_resume() where we can
++ * clear the signal_handler flag before resuming.
++ */
++void utrace_signal_handler(struct task_struct *task, int stepping)
++{
++ struct utrace *utrace = task->utrace;
++
++ spin_lock(&utrace->lock);
++
++ utrace->signal_handler = 1;
++ if (stepping) {
++ utrace->interrupt = 1;
++ set_tsk_thread_flag(task, TIF_SIGPENDING);
++ } else {
++ set_notify_resume(task);
++ }
++
++ spin_unlock(&utrace->lock);
++}
++
++/**
++ * utrace_prepare_examine - prepare to examine thread state
++ * @target: thread of interest, a &struct task_struct pointer
++ * @engine: engine pointer returned by utrace_attach_task()
++ * @exam: temporary state, a &struct utrace_examiner pointer
++ *
++ * This call prepares to safely examine the thread @target using
++ * &struct user_regset calls, or direct access to thread-synchronous fields.
++ *
++ * When @target is current, this call is superfluous. When @target is
++ * another thread, it must held stopped via %UTRACE_STOP by @engine.
++ *
++ * This call may block the caller until @target stays stopped, so it must
++ * be called only after the caller is sure @target is about to unschedule.
++ * This means a zero return from a utrace_control() call on @engine giving
++ * %UTRACE_STOP, or a report_quiesce() or report_signal() callback to
++ * @engine that used %UTRACE_STOP in its return value.
++ *
++ * Returns -%ESRCH if @target is dead or -%EINVAL if %UTRACE_STOP was
++ * not used. If @target has started running again despite %UTRACE_STOP
++ * (for %SIGKILL or a spurious wakeup), this call returns -%EAGAIN.
++ *
++ * When this call returns zero, it's safe to use &struct user_regset
++ * calls and task_user_regset_view() on @target and to examine some of
++ * its fields directly. When the examination is complete, a
++ * utrace_finish_examine() call must follow to check whether it was
++ * completed safely.
++ */
++int utrace_prepare_examine(struct task_struct *target,
++ struct utrace_attached_engine *engine,
++ struct utrace_examiner *exam)
++{
++ int ret = 0;
++
++ if (unlikely(target == current))
++ return 0;
++
++ rcu_read_lock();
++ if (unlikely(!engine_wants_stop(engine)))
++ ret = -EINVAL;
++ else if (unlikely(target->exit_state))
++ ret = -ESRCH;
++ else {
++ exam->state = target->state;
++ if (unlikely(exam->state == TASK_RUNNING))
++ ret = -EAGAIN;
++ else
++ get_task_struct(target);
++ }
++ rcu_read_unlock();
++
++ if (likely(!ret)) {
++ exam->ncsw = wait_task_inactive(target, exam->state);
++ put_task_struct(target);
++ if (unlikely(!exam->ncsw))
++ ret = -EAGAIN;
++ }
++
++ return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_prepare_examine);
++
++/**
++ * utrace_finish_examine - complete an examination of thread state
++ * @target: thread of interest, a &struct task_struct pointer
++ * @engine: engine pointer returned by utrace_attach_task()
++ * @exam: pointer passed to utrace_prepare_examine() call
++ *
++ * This call completes an examination on the thread @target begun by a
++ * paired utrace_prepare_examine() call with the same arguments that
++ * returned success (zero).
++ *
++ * When @target is current, this call is superfluous. When @target is
++ * another thread, this returns zero if @target has remained unscheduled
++ * since the paired utrace_prepare_examine() call returned zero.
++ *
++ * When this returns an error, any examination done since the paired
++ * utrace_prepare_examine() call is unreliable and the data extracted
++ * should be discarded. The error is -%EINVAL if @engine is not
++ * keeping @target stopped, or -%EAGAIN if @target woke up unexpectedly.
++ */
++int utrace_finish_examine(struct task_struct *target,
++ struct utrace_attached_engine *engine,
++ struct utrace_examiner *exam)
++{
++ int ret = 0;
++
++ if (unlikely(target == current))
++ return 0;
++
++ rcu_read_lock();
++ if (unlikely(!engine_wants_stop(engine)))
++ ret = -EINVAL;
++ else if (unlikely(target->state != exam->state))
++ ret = -EAGAIN;
++ else
++ get_task_struct(target);
++ rcu_read_unlock();
++
++ if (likely(!ret)) {
++ unsigned long ncsw = wait_task_inactive(target, exam->state);
++ if (unlikely(ncsw != exam->ncsw))
++ ret = -EAGAIN;
++ put_task_struct(target);
++ }
++
++ return ret;
++}
++EXPORT_SYMBOL_GPL(utrace_finish_examine);
++
++/*
++ * This is declared in linux/regset.h and defined in machine-dependent
++ * code. We put the export here to ensure no machine forgets it.
++ */
++EXPORT_SYMBOL_GPL(task_user_regset_view);
++
++/*
++ * Return the &struct task_struct for the task using ptrace on this one,
++ * or %NULL. Must be called with rcu_read_lock() held to keep the returned
++ * struct alive.
++ *
++ * At exec time, this may be called with task_lock() still held from when
++ * tracehook_unsafe_exec() was just called. In that case it must give
++ * results consistent with those unsafe_exec() results, i.e. non-%NULL if
++ * any %LSM_UNSAFE_PTRACE_* bits were set.
++ *
++ * The value is also used to display after "TracerPid:" in /proc/PID/status,
++ * where it is called with only rcu_read_lock() held.
++ */
++struct task_struct *utrace_tracer_task(struct task_struct *target)
++{
++ struct utrace *utrace;
++ struct task_struct *tracer = NULL;
++
++ utrace = rcu_dereference(target->utrace);
++ if (utrace != NULL) {
++ struct list_head *pos, *next;
++ struct utrace_attached_engine *engine;
++ const struct utrace_engine_ops *ops;
++ list_for_each_safe(pos, next, &utrace->attached) {
++ engine = list_entry(pos, struct utrace_attached_engine,
++ entry);
++ ops = rcu_dereference(engine->ops);
++ if (ops->tracer_task) {
++ tracer = (*ops->tracer_task)(engine, target);
++ if (tracer != NULL)
++ break;
++ }
++ }
++ }
++
++ return tracer;
++}
++
++/*
++ * Called on the current task to return LSM_UNSAFE_* bits implied by tracing.
++ * Called with task_lock() held.
++ */
++int utrace_unsafe_exec(struct task_struct *task)
++{
++ struct utrace *utrace = task->utrace;
++ struct utrace_attached_engine *engine, *next;
++ const struct utrace_engine_ops *ops;
++ int unsafe = 0;
++
++ list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
++ ops = rcu_dereference(engine->ops);
++ if (ops->unsafe_exec)
++ unsafe |= (*ops->unsafe_exec)(engine, task);
++ }
++
++ return unsafe;
++}
++
++/*
++ * Called with rcu_read_lock() held.
++ */
++void task_utrace_proc_status(struct seq_file *m, struct task_struct *p)
++{
++ struct utrace *utrace = rcu_dereference(p->utrace);
++ if (unlikely(utrace))
++ seq_printf(m, "Utrace: %lx%s%s%s\n",
++ p->utrace_flags,
++ utrace->stopped ? " (stopped)" : "",
++ utrace->report ? " (report)" : "",
++ utrace->interrupt ? " (interrupt)" : "");
++}
projects / people / pmueller / ipfire-2.x.git / blobdiff