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>
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 03cc061..58ed1da 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5148,7 +5148,7 @@
GFP_KERNEL);
if (!child_ctx) {
ret = -ENOMEM;
- goto exit;
+ break;
}
__perf_event_init_context(child_ctx, child);
@@ -5164,7 +5164,7 @@
}
}
- 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 @@
get_ctx(child_ctx->parent_ctx);
}
-exit:
mutex_unlock(&parent_ctx->mutex);
perf_unpin_context(parent_ctx);