From: Marco Elver Date: Thu, 27 May 2021 10:47:11 +0000 (+0200) Subject: perf: Fix data race between pin_count increment/decrement X-Git-Tag: v4.4.273~8 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=668bd53c549e1d6de8873c9037de98f042240b1e;p=thirdparty%2Fkernel%2Fstable.git perf: Fix data race between pin_count increment/decrement 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@syzkaller.appspotmail.com Signed-off-by: Marco Elver Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210527104711.2671610-1-elver@google.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/events/core.c b/kernel/events/core.c index d399748ea86b5..ee75563b724fd 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3497,7 +3497,9 @@ find_get_context(struct pmu *pmu, struct task_struct *task, 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; }