Haifeng Xu c81705d66f perf/core: Fix missing wakeup when waiting for context reference ... commit 74751ef5c1 upstream. 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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2024-06-21 14:35:55 +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	2024-06-21 14:35:55 +02:00
hw_breakpoint_test.c	perf/hw_breakpoint: test: Skip the test if dependencies unmet	2022-11-02 12:22:05 +01:00
hw_breakpoint.c	perf/hw_breakpoint: Annotate tsk->perf_event_mutex vs ctx->mutex	2022-10-04 13:32:09 +02:00
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/core: Bail out early if the request AUX area is out of bound	2023-11-28 17:06:54 +00:00
uprobes.c	mm/madvise: add file and shmem support to MADV_COLLAPSE	2022-10-03 14:03:33 -07:00