Ming Lei <[email protected]> writes:
> 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.
OK, but why the flag? Isn't moving the
blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
inside the lock sufficient?
Cheers,
Rusty.
>
> Cc: Jens Axboe <[email protected]>
> Cc: Rusty Russell <[email protected]>
> Signed-off-by: Ming Lei <[email protected]>
> ---
> drivers/block/virtio_blk.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 7a51f06..97f53ac 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -42,6 +42,9 @@ struct virtio_blk
> /* enable config space updates */
> bool config_enable;
>
> + /* if the request queue is stopped, protected by vq_lock */
> + bool queue_stopped;
> +
> /* What host tells us, plus 2 for header & tailer. */
> unsigned int sg_elems;
>
> @@ -147,11 +150,13 @@ static void virtblk_done(struct virtqueue *vq)
> if (unlikely(virtqueue_is_broken(vq)))
> break;
> } while (!virtqueue_enable_cb(vq));
> - spin_unlock_irqrestore(&vblk->vq_lock, flags);
>
> /* In case queue is stopped waiting for more buffers. */
> - if (req_done)
> + if (req_done && vblk->queue_stopped) {
> blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
> + vblk->queue_stopped = false;
> + }
> + spin_unlock_irqrestore(&vblk->vq_lock, flags);
> }
>
> static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
> @@ -205,8 +210,9 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> struct request *req)
> err = __virtblk_add_req(vblk->vq, vbr, vbr->sg, num);
> if (err) {
> virtqueue_kick(vblk->vq);
> - spin_unlock_irqrestore(&vblk->vq_lock, flags);
> blk_mq_stop_hw_queue(hctx);
> + vblk->queue_stopped = true;
> + spin_unlock_irqrestore(&vblk->vq_lock, flags);
> /* Out of mem doesn't actually happen, since we fall back
> * to direct descriptors */
> if (err == -ENOMEM || err == -ENOSPC)
> @@ -598,6 +604,7 @@ static int virtblk_probe(struct virtio_device *vdev)
> vblk->disk->fops = &virtblk_fops;
> vblk->disk->driverfs_dev = &vdev->dev;
> vblk->index = index;
> + vblk->queue_stopped = false;
>
> /* configure queue flush support */
> virtblk_update_cache_mode(vdev);
> --
> 1.7.9.5
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