linux-kernel - Re: [2.6.33-rc5] Weird deadlock when shutting down

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Message-ID: <a8e1da1002192342x7ca67176ta285db35ec6d34a6@mail.gmail.com>
Date:	Sat, 20 Feb 2010 15:42:56 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [2.6.33-rc5] Weird deadlock when shutting down

On Fri, Feb 19, 2010 at 2:45 AM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Thu, 2010-02-18 at 08:31 -0800, Linus Torvalds wrote:
>
>> > > halt/4071 is trying to acquire lock:
>> > >  (s_active){++++.+}, at: [<c0000000001ef868>]
>> > > .sysfs_addrm_finish+0x58/0xc0
>> > >
>> > > but task is already holding lock:
>> > >  (&per_cpu(cpu_policy_rwsem, cpu)){+.+.+.}, at:
>> [<c0000000004cd6ac>]
>> > > .lock_policy_rwsem_write+0x84/0xf4
>> > >
>> > > which lock already depends on the new lock.
>>
>> You don't have a full backtrace for these things?
>
> No, it deadlocks right there, unfortunately.
>
>> We've had lots of trouble with the cpu governors, and I suspect the
>> problem isn't new, but the lockdep warning is likely new (see commit
>> 846f99749ab68bbc7f75c74fec305de675b1a1bf: "sysfs: Add lockdep
>> annotations
>> for the sysfs active reference").
>>
>> So it is likely to be an old issue that (a) now gets warned about and
>> (b) might have had timing changes enough to trigger it.
>
> Well, it used to not deadlock and actually shut down the machine :) So
> in that sense it's definitely new. It might have printed a lockdep
> warning before, which you wouldn't normally see since the machine turns
> off right after this.

before shutdown, you can:
echo N > /proc/sys/kernel/printk_delay
to see the printk messages, N is 0-10000 in milliseconds

>
>> I suspect it is G5-specific (or specific to whatever CPU frequency
>> code
>> that gets used there), since I think we'd have had lots of reports if
>> this
>> happened on x86.
>
> Yeah, that's puzzling me as well.
>
> johannes
>



-- 
Regards
dave
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