[tip:perfcounters/core] perf_counter: Robustify counter-free logic

[tip-bot for Ingo Molnar]

Commit-ID:  012b84dae17126d8b5d159173091eb3db5a2bc43
Gitweb:     http://git.kernel.org/tip/012b84dae17126d8b5d159173091eb3db5a2bc43
Author:     Ingo Molnar <mingo@xxxxxxx>
AuthorDate: Sun, 17 May 2009 11:08:41 +0200
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Fri, 29 May 2009 14:28:37 +0200

perf_counter: Robustify counter-free logic

This fixes a nasty crash and highlights a bug that we were
freeing failed-fork() counters incorrectly.

(the fix for that will come separately)

[ Impact: fix crashes/lockups with inherited counters ]

Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Corey Ashford <cjashfor@xxxxxxxxxxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: John Kacur <jkacur@xxxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>


---
 kernel/perf_counter.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index eb34604..616c524 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1004,6 +1004,10 @@ static void __perf_counter_task_sched_out(struct perf_counter_context *ctx)
 
 	if (!cpuctx->task_ctx)
 		return;
+
+	if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
+		return;
+
 	__perf_counter_sched_out(ctx, cpuctx);
 	cpuctx->task_ctx = NULL;
 }
--
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