linux-kernel - Re: [PATCH 05/10] block: remove per-queue plugging

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 7 Mar 2011 09:07:35 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Shaohua Li <shli@...nel.org>
CC:	Mike Snitzer <snitzer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>
Subject: Re: [PATCH 05/10] block: remove per-queue plugging

On 2011-03-07 01:54, Shaohua Li wrote:
> 2011/3/5 Jens Axboe <jaxboe@...ionio.com>:
>> On 2011-03-04 22:43, Mike Snitzer wrote:
>>> On Fri, Mar 04 2011 at  8:02am -0500,
>>> Shaohua Li <shli@...nel.org> wrote:
>>>
>>>> 2011/3/4 Mike Snitzer <snitzer@...hat.com>:
>>>>> I'm now hitting a lockdep issue, while running a 'for-2.6.39/stack-plug'
>>>>> kernel, when I try an fsync heavy workload to a request-based mpath
>>>>> device (the kernel ultimately goes down in flames, I've yet to look at
>>>>> the crashdump I took)
>>>>>
>>>>>
>>>>> =======================================================
>>>>> [ INFO: possible circular locking dependency detected ]
>>>>> 2.6.38-rc6-snitm+ #2
>>>>> -------------------------------------------------------
>>>>> ffsb/3110 is trying to acquire lock:
>>>>>  (&(&q->__queue_lock)->rlock){..-...}, at: [<ffffffff811b4c4d>] flush_plug_list+0xbc/0x135
>>>>>
>>>>> but task is already holding lock:
>>>>>  (&rq->lock){-.-.-.}, at: [<ffffffff8137132f>] schedule+0x16a/0x725
>>>>>
>>>>> which lock already depends on the new lock.
>>>> I hit this too. Can you check if attached debug patch fixes it?
>>>
>>> Fixes it for me.
>>
>> The preempt bit in block/ should not be needed. Can you check whether
>> it's the moving of the flush in sched.c that does the trick?
> yes, it's not related to the lockdep issue. but I think we still need
> it. if there is a preempt  between attempt_plub_merge(), we do queue
> flush, then we might hit an incomplete list of request->biotail. Am I
> missing anything?

Ah, so it is needed with the other fix you proposed, since we do flush
on preempt then. If we only do the flush on going to sleep, then we
don't need that preemption disable in that section.

-- 
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/