linux-kernel - Re: [PATCH] virtio_blk: fix race between start and stop queue

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Message-ID: <53762662.2050702@kernel.dk>
Date:	Fri, 16 May 2014 08:53:22 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Ming Lei <tom.leiming@...il.com>, linux-kernel@...r.kernel.org
CC:	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] virtio_blk: fix race between start and stop queue

On 2014-05-15 06:33, Ming Lei wrote:
> When there isn't enough vring descriptor for adding to vq,
> blk-mq will be put as stopped state until some of pending
> descriptors are completed & freed.
>
> Unfortunately, the vq's interrupt may come just before
> blk-mq's BLK_MQ_S_STOPPED flag is set, so the blk-mq will
> still be kept as stopped even though lots of descriptors
> are completed and freed in the interrupt handler. The worst
> case is that all pending descriptors are freed in the
> interrupt handler, and the queue is kept as stopped forever.
>
> This patch fixes the problem by starting/stopping blk-mq
> with holding vq_lock.

Why not just use blk_mq_start_hw_queues()?

-- 
Jens Axboe

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