linux-kernel - Re: [PATCH 3/3] blk-mq: Fix the queue freezing mechanism

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Date:	Thu, 24 Sep 2015 15:54:18 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Ming Lei <tom.leiming@...il.com>, Jens Axboe <axboe@...com>,
	"Christoph Hellwig" <hch@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH 3/3] blk-mq: Fix the queue freezing mechanism

On 09/24/2015 11:14 AM, Tejun Heo wrote:
> On Thu, Sep 24, 2015 at 11:09:33AM -0700, Bart Van Assche wrote:
>> On 09/24/2015 10:49 AM, Tejun Heo wrote:
>>> Again, that doesn't happen.
>>
>> In case anyone would be interested, the backtraces for the lockup I had
>> observed are as follows:
>
> If this is happening and it's not caused by a hung in-flight request,
> it's either percpu_ref being buggy or the forementioned kill/reinit
> race screwing it up.  percpu_ref_kill() is expected to disable
> tryget_live() in a finite amount of time regardless of concurrent
> tryget tries.

Hello Tejun,

Sorry that I had not yet made this clear but I agreed with the analysis 
in your two most recent e-mails. I think I have found the cause of the 
loop: for one or another reason the scsi_dh_alua driver was not loaded 
automatically. I think that caused the SCSI core to return a retryable 
error code for reads and writes sent over paths in the SCSI ALUA state 
"standby" instead of a non-retryable error code and that that caused the 
dm-mpath driver to enter an infinite loop. Loading the scsi_dh_alua 
driver resolved the infinite loop. Anyway, thank you for the feedback.

Bart.

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