[PATCH] [1/275] perf session: Invalidate last_match when removing threads from rb_tree

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

[ upstream commit 70597f21f128b7dd6a2490078bea99d704b6f8c3 ]

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: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

---
 tools/perf/util/session.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6.35.y/tools/perf/util/session.c
===================================================================
--- linux-2.6.35.y.orig/tools/perf/util/session.c	2011-03-29 22:52:06.578019604 -0700
+++ linux-2.6.35.y/tools/perf/util/session.c	2011-03-29 23:02:58.140347711 -0700
@@ -134,6 +134,7 @@
 
 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
--
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