> From: Stefan Hajnoczi <stefa...@redhat.com>
> Sent: Wednesday, May 21, 2025 8:27 PM
>
> 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: sta...@vger.kernel.org
> > Reported-by: lirongq...@baidu.com
> > Closes:
> > https://lore.kernel.org/virtualization/c45dd68698cd47238c55fb73ca9b474
> > 1...@baidu.com/
> > Reviewed-by: Max Gurtovoy <mgurto...@nvidia.com>
> > Reviewed-by: Israel Rukshin <isra...@nvidia.com>
> > Signed-off-by: Parav Pandit <pa...@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.
On device removal all the VQs are broken. This check only uses a VQ to decide
on.
In future may be more elaborate API to have virtio_dev_broken() can be added.
Prefer to keep this patch without extending many APIs given it has Fixes tag.
>
> > +
> > + /* Start freezing the queue, so that new requests keeps waitng at
> > +the
>
> s/waitng/waiting/
>
Ack.
> > + * 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 shouldn't because vring_interrupt() also checks for the broken VQ before
invoking the _done().
Once the VQ is broken and even if _done() is invoked, it wont progress further
on get_buf().
And VQs are freed later in del_vq() after the device is reset as you suggested.
> It seems safer to reset the device before marking the requests as failed.
>
Such addition should be avoided because when the device is surprise removed,
even reset will not complete.
> > + 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
> >
