6.6-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ 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: c5ebcedb566e ("perf: Add ability to attach user stack dump to sample") Reported-by: Baisheng Gao baisheng.gao@unisoc.com Suggested-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20250605110815.GQ39944@noisy.programming.kicks-ass... Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/core.c | 7 +++++++ kernel/exit.c | 17 +++++++++-------- 2 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 563f39518f7fe..90577a7a3a51e 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6987,6 +6987,10 @@ 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 @@ -7685,6 +7689,9 @@ 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;
diff --git a/kernel/exit.c b/kernel/exit.c index 3540b2c9b1b6a..03a1dd32e6ff3 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -858,6 +858,15 @@ void __noreturn do_exit(long code) tsk->exit_code = code; taskstats_exit(tsk, group_dead);
+ /* + * Since sampling can touch ->mm, make sure to stop everything before we + * tear it down. + * + * Also flushes inherited counters to the parent - before the parent + * gets woken up by child-exit notifications. + */ + perf_event_exit_task(tsk); + exit_mm();
if (group_dead) @@ -874,14 +883,6 @@ void __noreturn do_exit(long code) exit_task_work(tsk); exit_thread(tsk);
- /* - * Flush inherited counters to the parent - before the parent - * gets woken up by child-exit notifications. - * - * because of cgroup mode, must be called before cgroup_exit() - */ - perf_event_exit_task(tsk); - sched_autogroup_exit_task(tsk); cgroup_exit(tsk);