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

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Date:	Mon, 2 Nov 2015 09:25:23 -0700
From:	Jens Axboe <axboe@...com>
To:	Paolo Valente <paolo.valente@...more.it>,
	Matias Bjørling <m@...rling.me>,
	Arianna Avanzini <avanzini@...gle.com>
CC:	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

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.

-- 
Jens Axboe

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