This is a note to let you know that I've just added the patch titled
perf: Fix data race between pin_count increment/decrement
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-fix-data-race-between-pin_count-increment-decrement.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6c605f8371159432ec61cbb1488dcf7ad24ad19a Mon Sep 17 00:00:00 2001
From: Marco Elver <elver@xxxxxxxxxx>
Date: Thu, 27 May 2021 12:47:11 +0200
Subject: perf: Fix data race between pin_count increment/decrement
From: Marco Elver <elver@xxxxxxxxxx>
commit 6c605f8371159432ec61cbb1488dcf7ad24ad19a upstream.
KCSAN reports a data race between increment and decrement of pin_count:
write to 0xffff888237c2d4e0 of 4 bytes by task 15740 on cpu 1:
find_get_context kernel/events/core.c:4617
__do_sys_perf_event_open kernel/events/core.c:12097 [inline]
__se_sys_perf_event_open kernel/events/core.c:11933
...
read to 0xffff888237c2d4e0 of 4 bytes by task 15743 on cpu 0:
perf_unpin_context kernel/events/core.c:1525 [inline]
__do_sys_perf_event_open kernel/events/core.c:12328 [inline]
__se_sys_perf_event_open kernel/events/core.c:11933
...
Because neither read-modify-write here is atomic, this can lead to one
of the operations being lost, resulting in an inconsistent pin_count.
Fix it by adding the missing locking in the CPU-event case.
Fixes: fe4b04fa31a6 ("perf: Cure task_oncpu_function_call() races")
Reported-by: syzbot+142c9018f5962db69c7e@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210527104711.2671610-1-elver@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/events/core.c | 2 ++
1 file changed, 2 insertions(+)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3497,7 +3497,9 @@ find_get_context(struct pmu *pmu, struct
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
ctx = &cpuctx->ctx;
get_ctx(ctx);
+ raw_spin_lock_irqsave(&ctx->lock, flags);
++ctx->pin_count;
+ raw_spin_unlock_irqrestore(&ctx->lock, flags);
return ctx;
}
Patches currently in stable-queue which might be from elver@xxxxxxxxxx are
queue-4.4/perf-fix-data-race-between-pin_count-increment-decrement.patch
