linux/kernel/events
Haifeng Xu 74751ef5c1 perf/core: Fix missing wakeup when waiting for context reference
In our production environment, we found many hung tasks which are
blocked for more than 18 hours. Their call traces are like this:

[346278.191038] __schedule+0x2d8/0x890
[346278.191046] schedule+0x4e/0xb0
[346278.191049] perf_event_free_task+0x220/0x270
[346278.191056] ? init_wait_var_entry+0x50/0x50
[346278.191060] copy_process+0x663/0x18d0
[346278.191068] kernel_clone+0x9d/0x3d0
[346278.191072] __do_sys_clone+0x5d/0x80
[346278.191076] __x64_sys_clone+0x25/0x30
[346278.191079] do_syscall_64+0x5c/0xc0
[346278.191083] ? syscall_exit_to_user_mode+0x27/0x50
[346278.191086] ? do_syscall_64+0x69/0xc0
[346278.191088] ? irqentry_exit_to_user_mode+0x9/0x20
[346278.191092] ? irqentry_exit+0x19/0x30
[346278.191095] ? exc_page_fault+0x89/0x160
[346278.191097] ? asm_exc_page_fault+0x8/0x30
[346278.191102] entry_SYSCALL_64_after_hwframe+0x44/0xae

The task was waiting for the refcount become to 1, but from the vmcore,
we found the refcount has already been 1. It seems that the task didn't
get woken up by perf_event_release_kernel() and got stuck forever. The
below scenario may cause the problem.

Thread A					Thread B
...						...
perf_event_free_task				perf_event_release_kernel
						   ...
						   acquire event->child_mutex
						   ...
						   get_ctx
   ...						   release event->child_mutex
   acquire ctx->mutex
   ...
   perf_free_event (acquire/release event->child_mutex)
   ...
   release ctx->mutex
   wait_var_event
						   acquire ctx->mutex
						   acquire event->child_mutex
						   # move existing events to free_list
						   release event->child_mutex
						   release ctx->mutex
						   put_ctx
...						...

In this case, all events of the ctx have been freed, so we couldn't
find the ctx in free_list and Thread A will miss the wakeup. It's thus
necessary to add a wakeup after dropping the reference.

Fixes: 1cf8dfe8a6 ("perf/core: Fix race between close() and fork()")
Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20240513103948.33570-1-haifeng.xu@shopee.com
2024-06-05 15:52:33 +02:00
..
callchain.c uaccess: remove CONFIG_SET_FS 2022-02-25 09:36:06 +01:00
core.c perf/core: Fix missing wakeup when waiting for context reference 2024-06-05 15:52:33 +02:00
hw_breakpoint_test.c perf/hw_breakpoint: remove MODULE_LICENSE in non-modules 2023-04-13 13:13:52 -07:00
hw_breakpoint.c perf/hw_breakpoint: Remove arch breakpoint hooks 2023-08-16 23:54:50 +10:00
internal.h perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled 2022-04-19 21:15:42 +02:00
Makefile perf/hw_breakpoint: Add KUnit test for constraints accounting 2022-08-30 10:56:20 +02:00
ring_buffer.c perf/ring_buffer: Trigger IO signals for watermark_wakeup 2024-04-14 22:26:32 +02:00
uprobes.c Probes updates for v6.10: 2024-05-17 18:29:30 -07:00