On Fri, May 25, 2012 at 10:34:48AM +0800, Asias He wrote:
> blk_cleanup_queue() will call blk_drian_queue() to drain all the
> requests before queue DEAD marking. If we reset the device before
> blk_cleanup_queue() the drain would fail.
>
> 1) if the queue is stopped in do_virtblk_request() because device is
> full, the q->request_fn() will not be called.
>
> blk_drain_queue() {
> while(true) {
> ...
> if (!list_empty(&q->queue_head))
> __blk_run_queue(q) {
> if (queue is not stoped)
> q->request_fn()
> }
> ...
> }
> }
>
> Do no reset the device before blk_cleanup_queue() gives the chance to
> start the queue in interrupt handler blk_done().
>
> 2) In commit b79d866c8b7014a51f611a64c40546109beaf24a, We abort requests
> dispatched to driver before blk_cleanup_queue(). There is a race if
> requests are dispatched to driver after the abort and before the queue
> DEAD mark. To fix this, instead of aborting the requests explicitly, we
> can just reset the device after after blk_cleanup_queue so that the
> device can complete all the requests before queue DEAD marking in the
> drain process.
>
> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx
> Signed-off-by: Asias He <asias@xxxxxxxxxx>
> ---
> drivers/block/virtio_blk.c | 12 +-----------
> 1 file changed, 1 insertion(+), 11 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 1bed517..b4fa2d7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -576,8 +576,6 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> {
> struct virtio_blk *vblk = vdev->priv;
> int index = vblk->index;
> - struct virtblk_req *vbr;
> - unsigned long flags;
>
> /* Prevent config work handler from accessing the device. */
> mutex_lock(&vblk->config_lock);
> @@ -585,21 +583,13 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> mutex_unlock(&vblk->config_lock);
>
> del_gendisk(vblk->disk);
> + blk_cleanup_queue(vblk->disk->queue);
Device is not reset here yet, so it will process
some requests in parallel with blk_cleanup_queue.
Is this a problem? Why not?
>
> /* Stop all the virtqueues. */
> vdev->config->reset(vdev);
>
> flush_work(&vblk->config_work);
>
> - /* Abort requests dispatched to driver. */
> - spin_lock_irqsave(&vblk->lock, flags);
> - while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {
> - __blk_end_request_all(vbr->req, -EIO);
> - mempool_free(vbr, vblk->pool);
> - }
> - spin_unlock_irqrestore(&vblk->lock, flags);
> -
> - blk_cleanup_queue(vblk->disk->queue);
> put_disk(vblk->disk);
> mempool_destroy(vblk->pool);
> vdev->config->del_vqs(vdev);
> --
> 1.7.10.2
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