[PATCH -stable 2.6.35.x] perf session: Invalidate last_match when removing threads from rb_tree

[PATCH -stable 2.6.35.x] perf session: Invalidate last_match when removing threads from rb_tree

[Frederic Weisbecker]

Hi,

This patch was applied few releases ago but lacked a tag
for stable.

Is it possible to backport it for 2.6.35.x?

Thanks.

---

commit 70597f21f128b7dd6a2490078bea99d704b6f8c3
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
Date:   Mon Aug 2 18:59:28 2010 -0300

perf session: Invalidate last_match when removing threads from rb_tree
    
If we receive two PERF_RECORD_EXIT for the same thread, we can end up
reusing session->last_match and trying to remove the thread twice from
the rb_tree, causing a segfault, so invalidade last_match in
perf_session__remove_thread.
  
Receiving two PERF_RECORD_EXIT for the same thread is a bug, but its a
harmless one if we make the tool more robust, like this patch does.
    
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: 2.6.35.x <stable@kernel.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 5d2fd52..fa9d652 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -166,6 +166,7 @@ void perf_session__delete(struct perf_session *self)
 
 void perf_session__remove_thread(struct perf_session *self, struct thread *th)
 {
+	self->last_match = NULL;
 	rb_erase(&th->rb_node, &self->threads);
 	/*
 	 * We may have references to this thread, for instance in some hist_entry