linux-kernel - Re: [PATCH BUGFIX 2/3] null_blk: guarantee device restart in all irq modes

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Date:	Tue, 3 Nov 2015 10:02:28 +0100
From:	Paolo Valente <paolo.valente@...more.it>
To:	Jens Axboe <axboe@...com>
Cc:	Matias Bjørling <m@...rling.me>,
	Arianna Avanzini <avanzini@...gle.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Ming Lei <ming.lei@...onical.com>,
	Mike Krinkin <krinkin.m.u@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH BUGFIX 2/3] null_blk: guarantee device restart in all irq modes


Il giorno 02/nov/2015, alle ore 17:25, Jens Axboe <axboe@...com> ha scritto:

> On 11/02/2015 07:31 AM, Paolo Valente wrote:
>> From: Arianna Avanzini <avanzini@...gle.com>
>> 
>> In single-queue (block layer) mode,the function null_rq_prep_fn stops
>> the device if alloc_cmd fails. Then, once stopped, the device must be
>> restarted on the next command completion, so that the request(s) for
>> which alloc_cmd failed can be requeued. Otherwise the device hangs.
>> 
>> Unfortunately, device restart is currently performed only for delayed
>> completions, i.e., in irqmode==2. This fact causes hangs, for the
>> above reasons, with the other irqmodes in combination with single-queue
>> block layer.
>> 
>> This commits addresses this issue by making sure that, if stopped, the
>> device is properly restarted for all irqmodes on completions.
> 
> This looks good. I did a double take at the removal of the q->mq_ops check before blk_queue_stopped(), but we can't get there in MQ mode. Perhaps a comment would be warranted for that, the ->mq_ops check served as a bit of documentation for that before.
> 

Honestly, I removed that additional check by mistake. I will put it back in the next version of this patchset, once (and if) I have the green light on patch 1/3.

Thanks,
Paolo

> -- 
> Jens Axboe
> 


--
Paolo Valente                                                 
Algogroup
Dipartimento di Fisica, Informatica e Matematica		
Via Campi, 213/B
41125 Modena - Italy        				  
homepage:  http://algogroup.unimore.it/people/paolo/

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