On Thu, May 03, 2012 at 03:30:47PM +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
>
> Changes in v2:
> - Drop req_in_flight
> - Use virtqueue_detach_unused_buf to get request dispatched to driver
>
> Signed-off-by: Asias He <[email protected]>
> ---
> drivers/block/virtio_blk.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 72fe55d..670c28f 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -443,7 +443,7 @@ 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;
Would be a bit easier to review if whitespace changes
are avoided, and done in a separate patch targeting 3.5.
> @@ -576,20 +576,30 @@ static void __devexit virtblk_remove(struct
> virtio_device *vdev)
> {
> struct virtio_blk *vblk = vdev->priv;
> int index = vblk->index;
> + struct virtblk_req *vbr;
>
> /* 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. */
All requests
Also, the comment isn't
really helpful. Want to explain why we abort
them all here? Won't they be drained
by later detach code?
> + blk_abort_queue(vblk->disk->queue);
> + del_gendisk(vblk->disk);
> +
> /* Stop all the virtqueues. */
> vdev->config->reset(vdev);
> -
> flush_work(&vblk->config_work);
>
> - del_gendisk(vblk->disk);
Is there a reason you move del_gendisk to before reset?
Is it safe to del_gendisk while we might
still be getting callbacks from the device?
> + /* Abort request dispatched to driver. */
> + while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {
> + blk_abort_request(vbr->req);
> + mempool_free(vbr, vblk->pool);
> + }
> +
> blk_cleanup_queue(vblk->disk->queue);
> put_disk(vblk->disk);
> +
> mempool_destroy(vblk->pool);
> vdev->config->del_vqs(vdev);
> kfree(vblk);
> --
> 1.7.10
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