--- /dev/null
+From b63e132b6433a41cf311e8bc382d33fd2b73b505 Mon Sep 17 00:00:00 2001
+From: Paul Burton <paul.burton@mips.com>
+Date: Fri, 22 Jun 2018 10:55:46 -0700
+Subject: MIPS: Use async IPIs for arch_trigger_cpumask_backtrace()
+
+From: Paul Burton <paul.burton@mips.com>
+
+commit b63e132b6433a41cf311e8bc382d33fd2b73b505 upstream.
+
+The current MIPS implementation of arch_trigger_cpumask_backtrace() is
+broken because it attempts to use synchronous IPIs despite the fact that
+it may be run with interrupts disabled.
+
+This means that when arch_trigger_cpumask_backtrace() is invoked, for
+example by the RCU CPU stall watchdog, we may:
+
+ - Deadlock due to use of synchronous IPIs with interrupts disabled,
+ causing the CPU that's attempting to generate the backtrace output
+ to hang itself.
+
+ - Not succeed in generating the desired output from remote CPUs.
+
+ - Produce warnings about this from smp_call_function_many(), for
+ example:
+
+ [42760.526910] INFO: rcu_sched detected stalls on CPUs/tasks:
+ [42760.535755] 0-...!: (1 GPs behind) idle=ade/140000000000000/0 softirq=526944/526945 fqs=0
+ [42760.547874] 1-...!: (0 ticks this GP) idle=e4a/140000000000000/0 softirq=547885/547885 fqs=0
+ [42760.559869] (detected by 2, t=2162 jiffies, g=266689, c=266688, q=33)
+ [42760.568927] ------------[ cut here ]------------
+ [42760.576146] WARNING: CPU: 2 PID: 1216 at kernel/smp.c:416 smp_call_function_many+0x88/0x20c
+ [42760.587839] Modules linked in:
+ [42760.593152] CPU: 2 PID: 1216 Comm: sh Not tainted 4.15.4-00373-gee058bb4d0c2 #2
+ [42760.603767] Stack : 8e09bd20 8e09bd20 8e09bd20 fffffff0 00000007 00000006 00000000 8e09bca8
+ [42760.616937] 95b2b379 95b2b379 807a0080 00000007 81944518 0000018a 00000032 00000000
+ [42760.630095] 00000000 00000030 80000000 00000000 806eca74 00000009 8017e2b8 000001a0
+ [42760.643169] 00000000 00000002 00000000 8e09baa4 00000008 808b8008 86d69080 8e09bca0
+ [42760.656282] 8e09ad50 805e20aa 00000000 00000000 00000000 8017e2b8 00000009 801070ca
+ [42760.669424] ...
+ [42760.673919] Call Trace:
+ [42760.678672] [<27fde568>] show_stack+0x70/0xf0
+ [42760.685417] [<84751641>] dump_stack+0xaa/0xd0
+ [42760.692188] [<699d671c>] __warn+0x80/0x92
+ [42760.698549] [<68915d41>] warn_slowpath_null+0x28/0x36
+ [42760.705912] [<f7c76c1c>] smp_call_function_many+0x88/0x20c
+ [42760.713696] [<6bbdfc2a>] arch_trigger_cpumask_backtrace+0x30/0x4a
+ [42760.722216] [<f845bd33>] rcu_dump_cpu_stacks+0x6a/0x98
+ [42760.729580] [<796e7629>] rcu_check_callbacks+0x672/0x6ac
+ [42760.737476] [<059b3b43>] update_process_times+0x18/0x34
+ [42760.744981] [<6eb94941>] tick_sched_handle.isra.5+0x26/0x38
+ [42760.752793] [<478d3d70>] tick_sched_timer+0x1c/0x50
+ [42760.759882] [<e56ea39f>] __hrtimer_run_queues+0xc6/0x226
+ [42760.767418] [<e88bbcae>] hrtimer_interrupt+0x88/0x19a
+ [42760.775031] [<6765a19e>] gic_compare_interrupt+0x2e/0x3a
+ [42760.782761] [<0558bf5f>] handle_percpu_devid_irq+0x78/0x168
+ [42760.790795] [<90c11ba2>] generic_handle_irq+0x1e/0x2c
+ [42760.798117] [<1b6d462c>] gic_handle_local_int+0x38/0x86
+ [42760.805545] [<b2ada1c7>] gic_irq_dispatch+0xa/0x14
+ [42760.812534] [<90c11ba2>] generic_handle_irq+0x1e/0x2c
+ [42760.820086] [<c7521934>] do_IRQ+0x16/0x20
+ [42760.826274] [<9aef3ce6>] plat_irq_dispatch+0x62/0x94
+ [42760.833458] [<6a94b53c>] except_vec_vi_end+0x70/0x78
+ [42760.840655] [<22284043>] smp_call_function_many+0x1ba/0x20c
+ [42760.848501] [<54022b58>] smp_call_function+0x1e/0x2c
+ [42760.855693] [<ab9fc705>] flush_tlb_mm+0x2a/0x98
+ [42760.862730] [<0844cdd0>] tlb_flush_mmu+0x1c/0x44
+ [42760.869628] [<cb259b74>] arch_tlb_finish_mmu+0x26/0x3e
+ [42760.877021] [<1aeaaf74>] tlb_finish_mmu+0x18/0x66
+ [42760.883907] [<b3fce717>] exit_mmap+0x76/0xea
+ [42760.890428] [<c4c8a2f6>] mmput+0x80/0x11a
+ [42760.896632] [<a41a08f4>] do_exit+0x1f4/0x80c
+ [42760.903158] [<ee01cef6>] do_group_exit+0x20/0x7e
+ [42760.909990] [<13fa8d54>] __wake_up_parent+0x0/0x1e
+ [42760.917045] [<46cf89d0>] smp_call_function_many+0x1a2/0x20c
+ [42760.924893] [<8c21a93b>] syscall_common+0x14/0x1c
+ [42760.931765] ---[ end trace 02aa09da9dc52a60 ]---
+ [42760.938342] ------------[ cut here ]------------
+ [42760.945311] WARNING: CPU: 2 PID: 1216 at kernel/smp.c:291 smp_call_function_single+0xee/0xf8
+ ...
+
+This patch switches MIPS' arch_trigger_cpumask_backtrace() to use async
+IPIs & smp_call_function_single_async() in order to resolve this
+problem. We ensure use of the pre-allocated call_single_data_t
+structures is serialized by maintaining a cpumask indicating that
+they're busy, and refusing to attempt to send an IPI when a CPU's bit is
+set in this mask. This should only happen if a CPU hasn't responded to a
+previous backtrace IPI - ie. if it's hung - and we print a warning to
+the console in this case.
+
+I've marked this for stable branches as far back as v4.9, to which it
+applies cleanly. Strictly speaking the faulty MIPS implementation can be
+traced further back to commit 856839b76836 ("MIPS: Add
+arch_trigger_all_cpu_backtrace() function") in v3.19, but kernel
+versions v3.19 through v4.8 will require further work to backport due to
+the rework performed in commit 9a01c3ed5cdb ("nmi_backtrace: add more
+trigger_*_cpu_backtrace() methods").
+
+Signed-off-by: Paul Burton <paul.burton@mips.com>
+Patchwork: https://patchwork.linux-mips.org/patch/19597/
+Cc: James Hogan <jhogan@kernel.org>
+Cc: Ralf Baechle <ralf@linux-mips.org>
+Cc: Huacai Chen <chenhc@lemote.com>
+Cc: linux-mips@linux-mips.org
+Cc: stable@vger.kernel.org # v4.9+
+Fixes: 856839b76836 ("MIPS: Add arch_trigger_all_cpu_backtrace() function")
+Fixes: 9a01c3ed5cdb ("nmi_backtrace: add more trigger_*_cpu_backtrace() methods")
+[ Huacai: backported to 4.9: Replace "call_single_data_t" with "struct call_single_data" ]
+Signed-off-by: Huacai Chen <chenhc@lemote.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/mips/kernel/process.c | 45 ++++++++++++++++++++++++++++++---------------
+ 1 file changed, 30 insertions(+), 15 deletions(-)
+
+--- a/arch/mips/kernel/process.c
++++ b/arch/mips/kernel/process.c
+@@ -26,6 +26,7 @@
+ #include <linux/kallsyms.h>
+ #include <linux/random.h>
+ #include <linux/prctl.h>
++#include <linux/nmi.h>
+
+ #include <asm/asm.h>
+ #include <asm/bootinfo.h>
+@@ -633,28 +634,42 @@ unsigned long arch_align_stack(unsigned
+ return sp & ALMASK;
+ }
+
+-static void arch_dump_stack(void *info)
+-{
+- struct pt_regs *regs;
++static DEFINE_PER_CPU(struct call_single_data, backtrace_csd);
++static struct cpumask backtrace_csd_busy;
+
+- regs = get_irq_regs();
+-
+- if (regs)
+- show_regs(regs);
+- else
+- dump_stack();
++static void handle_backtrace(void *info)
++{
++ nmi_cpu_backtrace(get_irq_regs());
++ cpumask_clear_cpu(smp_processor_id(), &backtrace_csd_busy);
+ }
+
+-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
++static void raise_backtrace(cpumask_t *mask)
+ {
+- long this_cpu = get_cpu();
++ struct call_single_data *csd;
++ int cpu;
+
+- if (cpumask_test_cpu(this_cpu, mask) && !exclude_self)
+- dump_stack();
++ for_each_cpu(cpu, mask) {
++ /*
++ * If we previously sent an IPI to the target CPU & it hasn't
++ * cleared its bit in the busy cpumask then it didn't handle
++ * our previous IPI & it's not safe for us to reuse the
++ * call_single_data_t.
++ */
++ if (cpumask_test_and_set_cpu(cpu, &backtrace_csd_busy)) {
++ pr_warn("Unable to send backtrace IPI to CPU%u - perhaps it hung?\n",
++ cpu);
++ continue;
++ }
+
+- smp_call_function_many(mask, arch_dump_stack, NULL, 1);
++ csd = &per_cpu(backtrace_csd, cpu);
++ csd->func = handle_backtrace;
++ smp_call_function_single_async(cpu, csd);
++ }
++}
+
+- put_cpu();
++void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
++{
++ nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace);
+ }
+
+ int mips_get_process_fp_mode(struct task_struct *task)
projects / thirdparty / kernel / stable-queue.git / commitdiff
