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 5.12-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-5.12 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 @@ -4542,7 +4542,9 @@ 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-5.12/perf-fix-data-race-between-pin_count-increment-decrement.patch