From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Thu, 6 May 2010 13:42:53 +0000 (+0200)
Subject: perf: Annotate perf_event_read_group() vs perf_event_release_kernel()
X-Git-Tag: v2.6.35-rc1~522^2~68
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a0507c84bf47dfd204299774f45fd16da33f0619;p=pandora-kernel.git

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>
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