linux-kernel - [tip:perfcounters/urgent] perf_counter: Fix double list iteration in per task precise stats

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Date:	Thu, 6 Aug 2009 18:28:00 GMT
From:	tip-bot for Peter Zijlstra <peterz@...radead.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Brice.Goglin@...ia.fr, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, peterz@...radead.org,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:perfcounters/urgent] perf_counter: Fix double list iteration in per task precise stats

Commit-ID:  1054598cab8674438675085fae459e960eb10799
Gitweb:     http://git.kernel.org/tip/1054598cab8674438675085fae459e960eb10799
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 6 Aug 2009 18:06:26 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Thu, 6 Aug 2009 20:25:18 +0200

perf_counter: Fix double list iteration in per task precise stats

Brice Goglin reported this crash with per task precise stats:

> I finally managed to test the threaded perfcounter statistics (thanks a
> lot for implementing it). I am running 2.6.31-rc5 (with the AMD
> magny-cours patches but I don't think they matter here). I am trying to
> measure local/remote memory accesses per thread during the well-known
> stream benchmark. It's compiled with OpenMP using 16 threads on a
> quad-socket quad-core barcelona machine.
>
> Command line is:
>  /mnt/scratch/bgoglin/cpunode/linux-2.6.31/tools/perf/perf record -f -s
> -e r1000001e0 -e r1000002e0 -e r1000004e0 -e r1000008e0 ./stream
>
> It seems to work fine with a single -e <counter> on the command line
> while it crashes when there are at least 2 of them.
> It seems to work fine without -s as well.

A silly copy-paste resulted in a messed up iteration which would
cause the OOPS.

Reported-by: Brice Goglin <Brice.Goglin@...ia.fr>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Tested-by: Brice Goglin <Brice.Goglin@...ia.fr>
LKML-Reference: <1249574786.32113.550.camel@...ns>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 kernel/perf_counter.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 199ed47..673c1aa 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1104,7 +1104,7 @@ static void perf_counter_sync_stat(struct perf_counter_context *ctx,
 		__perf_counter_sync_stat(counter, next_counter);
 
 		counter = list_next_entry(counter, event_entry);
-		next_counter = list_next_entry(counter, event_entry);
+		next_counter = list_next_entry(next_counter, event_entry);
 	}
 }
 
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