pthread_once hangs when init routine throws an exception [BZ #18435]

This is another attempt at making pthread_once handle throwing exceptions
from the init routine callback.  As the new testcases show, just switching
to the cleanup attribute based cleanup does fix the tst-once5 test, but
breaks the new tst-oncey3 test.  That is because when throwing exceptions,
only the unwind info registered cleanups (i.e. C++ destructors or cleanup
attribute), when cancelling threads and there has been unwind info from the
cancellation point up to whatever needs cleanup both unwind info registered
cleanups and THREAD_SETMEM (self, cleanup, ...) registered cleanups are
invoked, but once we hit some frame with no unwind info, only the
THREAD_SETMEM (self, cleanup, ...) registered cleanups are invoked.
So, to stay fully backwards compatible (allow init routines without
unwind info which encounter cancellation points) and handle exception throwing
we actually need to register the pthread_once cleanups in both unwind info
and in the THREAD_SETMEM (self, cleanup, ...) way.
If an exception is thrown, only the former will happen and we in that case
need to also unregister the THREAD_SETMEM (self, cleanup, ...) registered
handler, because otherwise after catching the exception the user code could
call deeper into the stack some cancellation point, get cancelled and then
a stale cleanup handler would clobber stack and probably crash.
If a thread calling init routine is cancelled and unwind info ends before
the pthread_once frame, it will be cleaned up through self->cleanup as
before.  And if unwind info is present, unwind_stop first calls the
self->cleanup registered handler for the frame, then it will call the
unwind info registered handler but that will already see __do_it == 0
and do nothing.

(cherry picked from commit f0419e6a10740a672b28e112c409ae24f5e890ab)

diff --git a/NEWS b/NEWS
index 55eed26d158bf435eeede0ad7611961ae5c382e1..94466f43a5b426567c6c9308436884af31035351 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -15,6 +15,7 @@ Major new features:
 
 The following bugs are resolved with this release:
 
+  [18435] pthread_once hangs when init routine throws an exception
   [23462] Static binary with dynamic string tokens ($LIB, $PLATFORM, $ORIGIN)
     crashes
   [27577] elf/ld.so --help doesn't work

diff --git a/nptl/Makefile b/nptl/Makefile
index 0282e07390e8a249febe3a5bb0d5e32d9b659b2d..5b036eb8a7b5d8b3a3bfcede26c17da9685d4041 100644 (file)
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -314,10 +314,6 @@ xtests += tst-eintr1
 
 test-srcs = tst-oddstacklimit
 
-# Test expected to fail on most targets (except x86_64) due to bug
-# 18435 - pthread_once hangs when init routine throws an exception.
-test-xfail-tst-once5 = yes
-
 gen-as-const-headers = unwindbuf.sym \
                       pthread-pi-defines.sym
 

diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index e5efa2e62d3d23d8f072182ece879288671ed3f6..79be1bc70f4e9db8c2ea793e7c44b6ae82c33fe0 100644 (file)
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -602,6 +602,67 @@ extern void __pthread_cleanup_pop (struct _pthread_cleanup_buffer *buffer,
 # undef pthread_cleanup_pop
 # define pthread_cleanup_pop(execute)                   \
   __pthread_cleanup_pop (&_buffer, (execute)); }
+
+# if defined __EXCEPTIONS && !defined __cplusplus
+/* Structure to hold the cleanup handler information.  */
+struct __pthread_cleanup_combined_frame
+{
+  void (*__cancel_routine) (void *);
+  void *__cancel_arg;
+  int __do_it;
+  struct _pthread_cleanup_buffer __buffer;
+};
+
+/* Special cleanup macros which register cleanup both using
+   __pthread_cleanup_{push,pop} and using cleanup attribute.  This is needed
+   for pthread_once, so that it supports both throwing exceptions from the
+   pthread_once callback (only cleanup attribute works there) and cancellation
+   of the thread running the callback if the callback or some routines it
+   calls don't have unwind information.  */
+
+static __always_inline void
+__pthread_cleanup_combined_routine (struct __pthread_cleanup_combined_frame
+                                   *__frame)
+{
+  if (__frame->__do_it)
+    {
+      __frame->__cancel_routine (__frame->__cancel_arg);
+      __frame->__do_it = 0;
+      __pthread_cleanup_pop (&__frame->__buffer, 0);
+    }
+}
+
+static inline void
+__pthread_cleanup_combined_routine_voidptr (void *__arg)
+{
+  struct __pthread_cleanup_combined_frame *__frame
+    = (struct __pthread_cleanup_combined_frame *) __arg;
+  if (__frame->__do_it)
+    {
+      __frame->__cancel_routine (__frame->__cancel_arg);
+      __frame->__do_it = 0;
+    }
+}
+
+#  define pthread_cleanup_combined_push(routine, arg) \
+  do {                                                                       \
+    void (*__cancel_routine) (void *) = (routine);                           \
+    struct __pthread_cleanup_combined_frame __clframe                        \
+      __attribute__ ((__cleanup__ (__pthread_cleanup_combined_routine)))      \
+      = { .__cancel_routine = __cancel_routine, .__cancel_arg = (arg),       \
+         .__do_it = 1 };                                                     \
+    __pthread_cleanup_push (&__clframe.__buffer,                             \
+                           __pthread_cleanup_combined_routine_voidptr,       \
+                           &__clframe);
+
+#  define pthread_cleanup_combined_pop(execute) \
+    __pthread_cleanup_pop (&__clframe.__buffer, 0);                          \
+    __clframe.__do_it = 0;                                                   \
+    if (execute)                                                             \
+      __cancel_routine (__clframe.__cancel_arg);                             \
+  } while (0)
+
+# endif
 #endif
 
 extern void __pthread_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer,

diff --git a/nptl/pthread_once.c b/nptl/pthread_once.c
index 28d97097c75f992d6b7c7e00f36155e040e2dcfa..7645da222a65bc3d3bec3715ba705ccacc5ee07b 100644 (file)
--- a/nptl/pthread_once.c
+++ b/nptl/pthread_once.c
@@ -111,11 +111,11 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
       /* This thread is the first here.  Do the initialization.
         Register a cleanup handler so that in case the thread gets
         interrupted the initialization can be restarted.  */
-      pthread_cleanup_push (clear_once_control, once_control);
+      pthread_cleanup_combined_push (clear_once_control, once_control);
 
       init_routine ();
 
-      pthread_cleanup_pop (0);
+      pthread_cleanup_combined_pop (0);
 
 
       /* Mark *once_control as having finished the initialization.  We need

diff --git a/nptl/tst-once5.cc b/nptl/tst-once5.cc
index b797ab35622e78eb67d6a55bf9e4ed6c0ac61e1b..60fe1ef820f3832caf53cddd31d0f6955bd5caf0 100644 (file)
--- a/nptl/tst-once5.cc
+++ b/nptl/tst-once5.cc
@@ -59,7 +59,7 @@ do_test (void)
                " throwing an exception", stderr);
     }
     catch (OnceException) {
-      if (1 < niter)
+      if (niter > 1)
         fputs ("pthread_once unexpectedly threw", stderr);
       result = 0;
     }
@@ -75,7 +75,5 @@ do_test (void)
   return result;
 }
 
-// The test currently hangs and is XFAILed.  Reduce the timeout.
-#define TIMEOUT 1
 #define TEST_FUNCTION do_test ()
 #include "../test-skeleton.c"

diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index eeb64f9fb0480ccc9919bb9a25a789278b6fc623..53b65ef3499ef8c90014e9416469d443dad13a9b 100644 (file)
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -231,7 +231,7 @@ generated += $(objpfx)tst-atfork2.mtrace \
 
 tests-internal += tst-cancel25 tst-robust8
 
-tests += tst-oncex3 tst-oncex4
+tests += tst-oncex3 tst-oncex4 tst-oncey3 tst-oncey4
 
 modules-names += tst-join7mod
 
@@ -242,6 +242,8 @@ endif
 
 CFLAGS-tst-oncex3.c += -fexceptions
 CFLAGS-tst-oncex4.c += -fexceptions
+CFLAGS-tst-oncey3.c += -fno-exceptions -fno-asynchronous-unwind-tables
+CFLAGS-tst-oncey4.c += -fno-exceptions -fno-asynchronous-unwind-tables
 
 $(objpfx)tst-join7: $(libdl) $(shared-thread-library)
 $(objpfx)tst-join7.out: $(objpfx)tst-join7mod.so

diff --git a/sysdeps/pthread/tst-oncey3.c b/sysdeps/pthread/tst-oncey3.c
new file mode 100644 (file)
index 0000000..08225b8
--- /dev/null
+++ b/sysdeps/pthread/tst-oncey3.c
@@ -0,0 +1 @@
+#include "tst-once3.c"

diff --git a/sysdeps/pthread/tst-oncey4.c b/sysdeps/pthread/tst-oncey4.c
new file mode 100644 (file)
index 0000000..9b4d98f
--- /dev/null
+++ b/sysdeps/pthread/tst-oncey4.c
@@ -0,0 +1 @@
+#include "tst-once4.c"