From: Mike Galbraith <efault@gmx.de>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Paul Mackerras <paulus@samba.org>
Subject: Re: [BUG] perf: hard lockup when using perf-sched
Date: Thu, 25 Mar 2010 10:27:21 +0100 [thread overview]
Message-ID: <1269509241.8438.30.camel@marge.simson.net> (raw)
In-Reply-To: <4BAB1924.4060304@cn.fujitsu.com>
On Thu, 2010-03-25 at 16:04 +0800, Li Zefan wrote:
> Mike Galbraith wrote:
> > On Wed, 2010-03-24 at 08:32 +0100, Mike Galbraith wrote:
> >
> >> I just saw this, hunted down your testcase and tried it here. Looks
> >> like perf_output_lock() wedged box.
> >
> > (turns on frame pointers, and adds noinline)
> >
>
> Thanks! Then who's going to fix this...
Well, that kinda depends on whether I figure out how the heck it's all
supposed to work before somebody else whacks it or not.
ATM, I've instrumented, know _what's_ happening, but find myself saying
"wtf?" a lot, especially wrt handle->locked. The act of attempting to
lock a handle declares it unlocked, turning perf_output_unlock() into a
noop, which looks a bit strange. We're spinning on those "unlocked"
locks, all left genuinely locked by one CPU. I just whacked the thing,
and am very likely about to see in yet another trace.
Locking is hard, "curious construct" locking is even harder :)
-Mike
next prev parent reply other threads:[~2010-03-25 9:27 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-17 7:21 [BUG] perf: hard lockup when using perf-sched Li Zefan
2010-03-24 5:52 ` Li Zefan
2010-03-24 7:32 ` Mike Galbraith
2010-03-24 8:17 ` Mike Galbraith
2010-03-25 8:04 ` Li Zefan
2010-03-25 9:27 ` Mike Galbraith [this message]
2010-03-25 9:54 ` Peter Zijlstra
2010-03-26 10:11 ` Mike Galbraith
2010-03-26 17:23 ` Frederic Weisbecker
2010-03-26 19:10 ` Mike Galbraith
2010-03-26 19:27 ` Frederic Weisbecker
2010-03-26 20:22 ` Mike Galbraith
2010-03-26 21:41 ` Frederic Weisbecker
2010-03-26 21:45 ` Frederic Weisbecker
2010-03-29 2:01 ` Li Zefan
2010-04-02 19:07 ` [tip:perf/core] perf: Fix 'perf sched record' deadlock tip-bot for Mike Galbraith
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