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perf: Fix NULL deref in inheritance code 

Liming found a NULL deref when a task has a perf context but no
counters  when it forks.

This can occur in two cases, a race during construction where
the fork hits after installing the context but before the first
counter gets inserted, or more reproducably, a fork after the
last counter is closed (which leaves the context around).

Reported-by: Wang Liming <liming.wang@windriver.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
CC: <stable@kernel.org>
LKML-Reference: <1262185684.7135.222.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-12-30 16:00:35 +01:00 committed by Ingo Molnar
parent 48b5ba9cc9
commit 05cbaa2853
1 changed files with 2 additions and 3 deletions
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5
kernel/perf_event.c
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@ -5148,7 +5148,7 @@ int perf_event_init_task(struct task_struct *child)
GFP_KERNEL);
if (!child_ctx) {
ret = -ENOMEM;
goto exit;
break;
}
__perf_event_init_context(child_ctx, child);
@ -5164,7 +5164,7 @@ int perf_event_init_task(struct task_struct *child)
}
}
if (inherited_all) {
if (child_ctx && inherited_all) {
/*
* Mark the child context as a clone of the parent
* context, or of whatever the parent is a clone of.
@ -5184,7 +5184,6 @@ int perf_event_init_task(struct task_struct *child)
get_ctx(child_ctx->parent_ctx);
}
exit:
mutex_unlock(&parent_ctx->mutex);
perf_unpin_context(parent_ctx);