tree d40bf7628ebb9935fb1ef6727337dcd9e2c94fd5
parent cce913178118b0b36742eb7544c2b38a0c957ee7
author Peter Zijlstra <a.p.zijlstra@chello.nl> 1273153373 +0200
committer Ingo Molnar <mingo@elte.hu> 1273224659 +0200

perf: Annotate perf_event_read_group() vs perf_event_release_kernel()

Stephane reported a lockdep warning while using PERF_FORMAT_GROUP.

The issue is that perf_event_read_group() takes faults while holding
the ctx->mutex, while perf_event_release_kernel() can be called from
munmap(). Which makes for an AB-BA deadlock.

Except we can never establish the deadlock because we'll only ever
call perf_event_release_kernel() after all file descriptors are dead
so there is no concurrency possible.

Reported-by: Stephane Eranian <eranian@google.com>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>