linux-kernel - Re: perf on 2.6.38-rc4 wedges my box

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Date:	Fri, 11 Feb 2011 18:53:26 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	David Ahern <dsahern@...il.com>
Cc:	Jeff Moyer <jmoyer@...hat.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf on 2.6.38-rc4 wedges my box

On Fri, 2011-02-11 at 09:35 -0700, David Ahern wrote:
> I'm guessing in your case perf is using hardware cycles for profiling.
> 
> I was able to reproduce the lockup in a VM which uses cpu-clock for
> profiling - like Jeff's case. The VM is running Fedora 14 with
> 2.6.38-rc4.
> 
Ah, indeed, when I use:

  perf record -gfe task-clock -- ./aio-stress -O -o 0 -r 4 -d 32 -b 16 /dev/sdb

things did come apart, something like the below cured that problem (but
did show the pending softirq thing and triggered something iffy in the
backtrace code -- will have to stare at those still)


---
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index a353a4d..36fb410 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5123,6 +5123,10 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
 	u64 period;
 
 	event = container_of(hrtimer, struct perf_event, hw.hrtimer);
+
+	if (event->state < PERF_EVENT_STATE_ACTIVE)
+		return HRTIMER_NORESTART;
+
 	event->pmu->read(event);
 
 	perf_sample_data_init(&data, 0);
@@ -5174,7 +5178,7 @@ static void perf_swevent_cancel_hrtimer(struct perf_event *event)
 		ktime_t remaining = hrtimer_get_remaining(&hwc->hrtimer);
 		local64_set(&hwc->period_left, ktime_to_ns(remaining));
 
-		hrtimer_cancel(&hwc->hrtimer);
+		hrtimer_try_to_cancel(&hwc->hrtimer);
 	}
 }
 


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