> From: Michael S. Tsirkin <m...@redhat.com>
> Sent: Thursday, May 29, 2025 1:34 PM
>
> 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: sta...@vger.kernel.org
> > Reported-by: Li RongQing <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>
> >
> > ---
> > 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.
> */
>
Ok. will add.
> > +{
> > + 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:
>
Virtblk_cleanup_broken_device()?
Is that name ok?
> /*
> * 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.
> */
>
Will add it.
>
> > +{
> > + 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.
>
Ok. will move.
>
> > +
> > + /* 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
> */
>
Ok. will fix it.
> > + * 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
>
Will fix it.
> > + * 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?
>
Will fix this too.
> > + * 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
>
>
Ok.
> > + * 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.
>
No strong preference, some maintainers prefer the current way others the way
you preferred.
So will fix as you proposed here along with above fixes in v4.
Thanks
>
> > del_gendisk(vblk->disk);
> > blk_mq_free_tag_set(&vblk->tag_set);
> >
> > --
> > 2.34.1
