On Thu, May 29, 2025 at 06:19:31AM +0000, Parav Pandit wrote:
> When the PCI device is surprise removed, requests may not complete
> the device as the VQ is marked as broken. Due to this, the disk
> deletion hangs.
>
> Fix it by aborting the requests when the VQ is broken.
>
> With this fix now fio completes swiftly.
> An alternative of IO timeout has been considered, however
> when the driver knows about unresponsive block device, swiftly clearing
> them enables users and upper layers to react quickly.
>
> Verified with multiple device unplug iterations with pending requests in
> virtio used ring and some pending with the device.
>
> Fixes: 43bb40c5b926 ("virtio_pci: Support surprise removal of virtio pci device")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Li RongQing <lirongqing@xxxxxxxxx>
> Closes: https://lore.kernel.org/virtualization/c45dd68698cd47238c55fb73ca9b4741@xxxxxxxxx/
> Reviewed-by: Max Gurtovoy <mgurtovoy@xxxxxxxxxx>
> Reviewed-by: Israel Rukshin <israelr@xxxxxxxxxx>
> Signed-off-by: Parav Pandit <parav@xxxxxxxxxx>
>
> ---
> v2->v3:
> - Addressed comments from Michael
> - updated comment for synchronizing with callbacks
>
> v1->v2:
> - Addressed comments from Stephan
> - fixed spelling to 'waiting'
> - Addressed comments from Michael
> - Dropped checking broken vq from queue_rq() and queue_rqs()
> because it is checked in lower layer routines in virtio core
>
> v0->v1:
> - Fixed comments from Stefan to rename a cleanup function
> - Improved logic for handling any outstanding requests
> in bio layer
> - improved cancel callback to sync with ongoing done()
Thanks!
Something else small to improve.
> ---
> drivers/block/virtio_blk.c | 82 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 82 insertions(+)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 7cffea01d868..d37df878f4e9 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1554,6 +1554,86 @@ static int virtblk_probe(struct virtio_device *vdev)
> return err;
> }
>
> +static bool virtblk_request_cancel(struct request *rq, void *data)
it is more
virtblk_request_complete_broken_with_ioerr
and maybe a comment?
/*
* If the vq is broken, device will not complete requests.
* So we do it for the device.
*/
> +{
> + struct virtblk_req *vbr = blk_mq_rq_to_pdu(rq);
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq;
> + unsigned long flags;
> +
> + vq = &vblk->vqs[rq->mq_hctx->queue_num];
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + vbr->in_hdr.status = VIRTIO_BLK_S_IOERR;
> + if (blk_mq_request_started(rq) && !blk_mq_request_completed(rq))
> + blk_mq_complete_request(rq);
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> + return true;
> +}
> +
> +static void virtblk_broken_device_cleanup(struct virtio_blk *vblk)
and one goes okay what does it do exactly? cleanup device in
a broken way? turns out no, it cleans up a broken device.
And an overview would be good. Maybe, a small comment will help:
/*
* if the device is broken, it will not use any buffers and waiting
* for that to happen is pointless. We'll do it in the driver,
* completing all requests for the device.
*/
> +{
> + struct request_queue *q = vblk->disk->queue;
> +
> + if (!virtqueue_is_broken(vblk->vqs[0].vq))
> + return;
so one has to read it, and understand that we did not need to call
it in the 1st place on a non broken device.
Moving it to the caller would be cleaner.
> +
> + /* Start freezing the queue, so that new requests keeps waiting at the
wrong style of comment for blk.
/* this is
* net style
*/
/*
* this is
* rest of the linux style
*/
> + * door of bio_queue_enter(). We cannot fully freeze the queue because
> + * freezed queue is an empty queue and there are pending requests, so
a frozen queue
> + * only start freezing it.
> + */
> + blk_freeze_queue_start(q);
> +
> + /* When quiescing completes, all ongoing dispatches have completed
> + * and no new dispatch will happen towards the driver.
> + * This ensures that later when cancel is attempted, then are not
they are not?
> + * getting processed by the queue_rq() or queue_rqs() handlers.
> + */
> + blk_mq_quiesce_queue(q);
> +
> + /*
> + * Synchronize with any ongoing VQ callbacks that may have started
> + * before the VQs were marked as broken. Any outstanding requests
> + * will be completed by virtblk_request_cancel().
> + */
> + virtio_synchronize_cbs(vblk->vdev);
> +
> + /* At this point, no new requests can enter the queue_rq() and
> + * completion routine will not complete any new requests either for the
> + * broken vq. Hence, it is safe to cancel all requests which are
> + * started.
> + */
> + blk_mq_tagset_busy_iter(&vblk->tag_set, virtblk_request_cancel, vblk);
> + blk_mq_tagset_wait_completed_request(&vblk->tag_set);
> +
> + /* All pending requests are cleaned up. Time to resume so that disk
> + * deletion can be smooth. Start the HW queues so that when queue is
> + * unquiesced requests can again enter the driver.
> + */
> + blk_mq_start_stopped_hw_queues(q, true);
> +
> + /* Unquiescing will trigger dispatching any pending requests to the
> + * driver which has crossed bio_queue_enter() to the driver.
> + */
> + blk_mq_unquiesce_queue(q);
> +
> + /* Wait for all pending dispatches to terminate which may have been
> + * initiated after unquiescing.
> + */
> + blk_mq_freeze_queue_wait(q);
> +
> + /* Mark the disk dead so that once queue unfreeze, the requests
... once we unfreeze the queue
> + * waiting at the door of bio_queue_enter() can be aborted right away.
> + */
> + blk_mark_disk_dead(vblk->disk);
> +
> + /* Unfreeze the queue so that any waiting requests will be aborted. */
> + blk_mq_unfreeze_queue_nomemrestore(q);
> +}
> +
> static void virtblk_remove(struct virtio_device *vdev)
> {
> struct virtio_blk *vblk = vdev->priv;
> @@ -1561,6 +1641,8 @@ static void virtblk_remove(struct virtio_device *vdev)
> /* Make sure no work handler is accessing the device. */
> flush_work(&vblk->config_work);
>
I prefer simply moving the test here:
if (virtqueue_is_broken(vblk->vqs[0].vq))
virtblk_broken_device_cleanup(vblk);
makes it much clearer what is going on, imho.
> del_gendisk(vblk->disk);
> blk_mq_free_tag_set(&vblk->tag_set);
>
> --
> 2.34.1
