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

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Message-ID: <4D70E705.1080309@fusionio.com>
Date:	Fri, 4 Mar 2011 14:20:05 +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 2011-03-04 14:02, Shaohua Li 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?

I'll take a look at this. It would be really nice if we could move the
plug flush outside of the runqueue lock.

-- 
Jens Axboe

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