Re: [PATCH v1] virtio_blk: fix race between start and stop queue

From: Jens Axboe
Date: Fri May 16 2014 - 11:33:00 EST


On 2014-05-16 09:31, 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.

Thanks, this looks good, I'll apply it for 3.16 (with a stable marker, even if it is an unlikely event).

--
Jens Axboe

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