> From: Michael S. Tsirkin <m...@redhat.com>
> Sent: 25 June 2025 12:37 AM
>
> On Tue, Jun 24, 2025 at 07:01:44PM +0000, Parav Pandit wrote:
> >
> >
> > > From: Stefan Hajnoczi <stefa...@redhat.com>
> > > Sent: 25 June 2025 12:26 AM
> > >
> > > On Mon, Jun 02, 2025 at 02:44:33AM +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.
> > >
> > > There are loops in the core virtio driver code that expect device
> > > register reads to eventually return 0:
> > > drivers/virtio/virtio_pci_modern.c:vp_reset()
> > > drivers/virtio/virtio_pci_modern_dev.c:vp_modern_set_queue_reset()
> > >
> > > Is there a hang if these loops are hit when a device has been
> > > surprise removed? I'm trying to understand whether surprise removal
> > > is fully supported or whether this patch is one step in that direction.
> > >
> > In one of the previous replies I answered to Michael, but don't have the
> > link
> handy.
> > It is not fully supported by this patch. It will hang.
> >
> > This patch restores driver back to the same state what it was before the
> > fixes
> tag patch.
> > The virtio stack level work is needed to support surprise removal, including
> the reset flow you rightly pointed.
>
> Have plans to do that?
>
Didn't give enough thoughts on it yet.
> > > Apart from that, I'm happy with the virtio_blk.c aspects of the patch:
> > > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
> > >
> > Thanks.
> >
> > > >
> > > > 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/c45dd68698cd47238c55fb73ca9
> > > > b474
> > > > 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>
> > > >
> > > > ---
> > > > v4->v5:
> > > > - fixed comment style where comment to start with one empty line
> > > > at start
> > > > - Addressed comments from Alok
> > > > - fixed typo in broken vq check
> > > > v3->v4:
> > > > - Addressed comments from Michael
> > > > - renamed virtblk_request_cancel() to
> > > > virtblk_complete_request_with_ioerr()
> > > > - Added comments for virtblk_complete_request_with_ioerr()
> > > > - Renamed virtblk_broken_device_cleanup() to
> > > > virtblk_cleanup_broken_device()
> > > > - Added comments for virtblk_cleanup_broken_device()
> > > > - Moved the broken vq check in virtblk_remove()
> > > > - Fixed comment style to have first empty line
> > > > - replaced freezed to frozen
> > > > - Fixed comments rephrased
> > > >
> > > > 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()
> > > > ---
> > > > 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..c5e383c0ac48
> > > > 100644
> > > > --- a/drivers/block/virtio_blk.c
> > > > +++ b/drivers/block/virtio_blk.c
> > > > @@ -1554,6 +1554,98 @@ static int virtblk_probe(struct
> > > > virtio_device
> > > *vdev)
> > > > return err;
> > > > }
> > > >
> > > > +/*
> > > > + * If the vq is broken, device will not complete requests.
> > > > + * So we do it for the device.
> > > > + */
> > > > +static bool virtblk_complete_request_with_ioerr(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;
> > > > +}
> > > > +
> > > > +/*
> > > > + * If the device is broken, it will not use any buffers and
> > > > +waiting
> > > > + * for that to happen is pointless. We'll do the cleanup in the
> > > > +driver,
> > > > + * completing all requests for the device.
> > > > + */
> > > > +static void virtblk_cleanup_broken_device(struct virtio_blk *vblk) {
> > > > + struct request_queue *q = vblk->disk->queue;
> > > > +
> > > > + /*
> > > > + * Start freezing the queue, so that new requests keeps waiting
> > > > at the
> > > > + * door of bio_queue_enter(). We cannot fully freeze the queue
> > > because
> > > > + * frozen 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.
> > > > + */
> > > > + 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_complete_request_with_ioerr().
> > > > + */
> > > > + 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_complete_request_with_ioerr,
> > > > 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 we unfreeze the queue,
> > > > 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 +1653,9 @@
> > > > static void virtblk_remove(struct virtio_device *vdev)
> > > > /* Make sure no work handler is accessing the device. */
> > > > flush_work(&vblk->config_work);
> > > >
> > > > + if (virtqueue_is_broken(vblk->vqs[0].vq))
> > > > + virtblk_cleanup_broken_device(vblk);
> > > > +
> > > > del_gendisk(vblk->disk);
> > > > blk_mq_free_tag_set(&vblk->tag_set);
> > > >
> > > > --
> > > > 2.34.1
> > > >
