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

From: Jens Axboe
Date: Mon Nov 02 2015 - 11:25:46 EST

On 11/02/2015 07:31 AM, Paolo Valente wrote:
From: Arianna Avanzini <avanzini@xxxxxxxxxx>

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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