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perf: Fix sample vs do_exit()

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[ Upstream commit 4f6fc782128355931527cefe3eb45338abd8ab39 ]

Baisheng Gao reported an ARM64 crash, which Mark decoded as being a
synchronous external abort -- most likely due to trying to access
MMIO in bad ways.

The crash further shows perf trying to do a user stack sample while in
exit_mmap()'s tlb_finish_mmu() -- i.e. while tearing down the address
space it is trying to access.

It turns out that we stop perf after we tear down the userspace mm; a
receipie for disaster, since perf likes to access userspace for
various reasons.

Flip this order by moving up where we stop perf in do_exit().

Additionally, harden PERF_SAMPLE_CALLCHAIN and PERF_SAMPLE_STACK_USER
to abort when the current task does not have an mm (exit_mm() makes
sure to set current->mm = NULL; before commencing with the actual
teardown). Such that CPU wide events don't trip on this same problem.

Fixes: c5ebcedb56 ("perf: Add ability to attach user stack dump to sample")
Reported-by: Baisheng Gao <[email protected]>
Suggested-by: Mark Rutland <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Peter Zijlstra 2025-06-05 12:31:45 +02:00 • committed by Greg Kroah-Hartman
commit 7b8f3c7217
2 changed files with 16 additions and 8 deletions
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7
kernel/events/core.c
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@ -6219,6 +6219,10 @@ perf_sample_ustack_size(u16 stack_size, u16 header_size,
if (!regs)
return 0;
/* No mm, no stack, no dump. */
if (!current->mm)
return 0;
/*
* Check if we fit in with the requested stack size into the:
* - TASK_SIZE
@ -6687,6 +6691,9 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
const u32 max_stack = event->attr.sample_max_stack;
struct perf_callchain_entry *callchain;
if (!current->mm)
user = false;
if (!kernel && !user)
return &__empty_callchain;