New subject: [PATCH v1] virtio_blk: Fix disk deletion hang on device surprise removal

21 May 2025

On Wed, May 21, 2025 at 06:37:41AM +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@vger.kernel.org
Reported-by: lirongqing@baidu.com
Closes: https://lore.kernel.org/virtualization/c45dd68698cd47238c55fb73ca9b4741@baid...
Reviewed-by: Max Gurtovoy mgurtovoy@nvidia.com
Reviewed-by: Israel Rukshin israelr@nvidia.com
Signed-off-by: Parav Pandit parav@nvidia.com

changelog:
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()


drivers/block/virtio_blk.c | 95 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 7cffea01d868..5212afdbd3c7 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -435,6 +435,13 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
   blk_status_t status;
   int err;

/* Immediately fail all incoming requests if the vq is broken.
* Once the queue is unquiesced, upper block layer flushes any pending


* queued requests; fail them right away.


*/


if (unlikely(virtqueue_is_broken(vblk->vqs[qid].vq)))
return BLK_STS_IOERR;


status = virtblk_prep_rq(hctx, vblk, req, vbr);
 if (unlikely(status))
  return status;

@@ -508,6 +515,11 @@ static void virtio_queue_rqs(struct rq_list *rqlist)
   while ((req = rq_list_pop(rqlist))) {
   	struct virtio_blk_vq *this_vq = get_virtio_blk_vq(req->mq_hctx);

if (unlikely(virtqueue_is_broken(this_vq->vq))) {


	rq_list_add_tail(&requeue_list, req);


	continue;


}


if (vq && vq != this_vq)
  	virtblk_add_req_batch(vq, &submit_list);
  vq = this_vq;

@@ -1554,6 +1566,87 @@ static int virtblk_probe(struct virtio_device *vdev)
   return err;
 }
 
+static bool virtblk_request_cancel(struct request *rq, void *data)
+{

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)
+{

struct request_queue *q = vblk->disk->queue;

if (!virtqueue_is_broken(vblk->vqs[0].vq))
return;



Can a subset of virtqueues be broken? If so, then this code doesn't
handle it.
...


/* Start freezing the queue, so that new requests keeps waitng at the

s/waitng/waiting/
...

* door of bio_queue_enter(). We cannot fully freeze the queue because


* freezed queue is an empty queue and there are pending requests, so


* 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


* getting processed by the queue_rq() or queue_rqs() handlers.


*/


blk_mq_quiesce_queue(q);

/*
* Synchronize with any ongoing VQ callbacks, effectively quiescing


* the device and preventing it from completing further requests


* to the block layer. Any outstanding, incomplete 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);

Although virtio_synchronize_cbs() was called, a broken/malicious device
can still raise IRQs. Would that lead to use-after-free or similar
undefined behavior for requests that have been submitted to the device?
It seems safer to reset the device before marking the requests as
failed.
...

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
* 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 +1654,8 @@ static void virtblk_remove(struct virtio_device *vdev)
   /* Make sure no work handler is accessing the device. */
   flush_work(&vblk->config_work);

virtblk_broken_device_cleanup(vblk);
del_gendisk(vblk->disk);
 blk_mq_free_tag_set(&vblk->tag_set);


2.34.1

    

Re: [PATCH v1] virtio_blk: Fix disk deletion hang on device surprise removal