On Thu, May 03, 2012 at 10:19:52AM +0800, Asias He wrote:
> If we reset the virtio-blk device before the requests already dispatched
> to the virtio-blk driver from the block layer are finised, we will stuck
> in blk_cleanup_queue() and the remove will fail.
>
> blk_cleanup_queue() calls blk_drain_queue() to drain all requests queued
> before DEAD marking. However it will never success if the device is
> already stopped. We'll have q->in_flight[] > 0, so the drain will not
> finish.
>
> How to reproduce the race:
> 1. hot-plug a virtio-blk device
> 2. keep reading/writing the device in guest
> 3. hot-unplug while the device is busy serving I/O
>
> Signed-off-by: Asias He <asias@xxxxxxxxxx>
We used to do similar tracking in -net but dropped it all by using the
tracking that virtio core does. Can't blk do the same? Isn't there
some way to use virtqueue_detach_unused_buf for this instead?
> ---
> drivers/block/virtio_blk.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 72fe55d..72b818b 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -46,6 +46,9 @@ struct virtio_blk
> /* Ida index - used to track minor number allocations. */
> int index;
>
> + /* Number of pending requests dispatched to driver. */
> + int req_in_flight;
> +
> /* Scatterlist: can be too big for stack. */
> struct scatterlist sg[/*sg_elems*/];
> };
> @@ -95,6 +98,7 @@ static void blk_done(struct virtqueue *vq)
> }
>
> __blk_end_request_all(vbr->req, error);
> + vblk->req_in_flight--;
> mempool_free(vbr, vblk->pool);
> }
> /* In case queue is stopped waiting for more buffers. */
> @@ -190,6 +194,7 @@ static void do_virtblk_request(struct request_queue *q)
>
> while ((req = blk_peek_request(q)) != NULL) {
> BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
> + vblk->req_in_flight++;
>
> /* If this request fails, stop queue and wait for something to
> finish to restart it. */
> @@ -443,7 +448,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
> if (err)
> goto out_free_vblk;
>
> - vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
> + vblk->pool = mempool_create_kmalloc_pool(1, sizeof(struct virtblk_req));
> if (!vblk->pool) {
> err = -ENOMEM;
> goto out_free_vq;
> @@ -466,6 +471,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
>
> virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN);
>
> + vblk->req_in_flight = 0;
> vblk->disk->major = major;
> vblk->disk->first_minor = index_to_minor(index);
> vblk->disk->private_data = vblk;
> @@ -576,22 +582,34 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
> {
> struct virtio_blk *vblk = vdev->priv;
> int index = vblk->index;
> + unsigned long flags;
> + int req_in_flight;
>
> /* Prevent config work handler from accessing the device. */
> mutex_lock(&vblk->config_lock);
> vblk->config_enable = false;
> mutex_unlock(&vblk->config_lock);
>
> + /* Abort all request on the queue. */
> + blk_abort_queue(vblk->disk->queue);
> + del_gendisk(vblk->disk);
> +
> /* Stop all the virtqueues. */
> vdev->config->reset(vdev);
> -
> + vdev->config->del_vqs(vdev);
> flush_work(&vblk->config_work);
>
> - del_gendisk(vblk->disk);
> + /* Wait requests dispatched to device driver to finish. */
> + do {
> + spin_lock_irqsave(&vblk->lock, flags);
> + req_in_flight = vblk->req_in_flight;
> + spin_unlock_irqrestore(&vblk->lock, flags);
> + } while (req_in_flight != 0);
> +
> blk_cleanup_queue(vblk->disk->queue);
> put_disk(vblk->disk);
> +
> mempool_destroy(vblk->pool);
> - vdev->config->del_vqs(vdev);
> kfree(vblk);
> ida_simple_remove(&vd_index_ida, index);
> }
> --
> 1.7.10
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