linux-kernel - [PATCH] perf_counter: fix double list iteration

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Date:	Thu, 06 Aug 2009 18:06:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] perf_counter: fix double list iteration

On Thu, 2009-08-06 at 17:38 +0200, Peter Zijlstra wrote:
> On Thu, 2009-08-06 at 08:26 +0200, Brice Goglin wrote:
> > Hello Ingo
> > 
> > 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.
> 
> OK, I can reproduce OOPSen this way, got me baffled though.
> 
> I'll prod at it some...

D'0h really dumb mistake...

---
Subject: perf_counter: fix double list iteration

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

Reported-by: Brice Goglin <Brice.Goglin@...ia.fr>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 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 06d210c..6da7611 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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