> From: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Sent: Wednesday, February 21, 2024 3:35 AM
> To: Parav Pandit <parav@xxxxxxxxxx>
>
> On Sat, Feb 17, 2024 at 08:08:48PM +0200, Parav Pandit wrote:
> > When the PCI device is surprise removed, requests won't complete from
> > the device. These IOs are never completed and disk deletion hangs
> > indefinitely.
> >
> > Fix it by aborting the IOs which the device will never complete 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 cycles with pending IOs in virtio
> > used ring and some pending with device.
> >
> > In future instead of VQ broken, a more elegant method can be used. At
> > the moment the patch is kept to its minimal changes given its urgency
> > to fix broken kernels.
> >
> > Fixes: 43bb40c5b926 ("virtio_pci: Support surprise removal of virtio
> > pci device")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reported-by: lirongqing@xxxxxxxxx
> > Closes:
> > https://lore.kernel.org/virtualization/c45dd68698cd47238c55fb73ca9b474
> > 1@xxxxxxxxx/
> > Co-developed-by: Chaitanya Kulkarni <kch@xxxxxxxxxx>
> > Signed-off-by: Chaitanya Kulkarni <kch@xxxxxxxxxx>
> > Signed-off-by: Parav Pandit <parav@xxxxxxxxxx>
> > ---
> > drivers/block/virtio_blk.c | 54
> > ++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 54 insertions(+)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 2bf14a0e2815..59b49899b229 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -1562,10 +1562,64 @@ static int virtblk_probe(struct virtio_device
> *vdev)
> > return err;
> > }
> >
> > +static bool virtblk_cancel_request(struct request *rq, void *data) {
> > + struct virtblk_req *vbr = blk_mq_rq_to_pdu(rq);
> > +
> > + vbr->in_hdr.status = VIRTIO_BLK_S_IOERR;
> > + if (blk_mq_request_started(rq) && !blk_mq_request_completed(rq))
> > + blk_mq_complete_request(rq);
> > +
> > + return true;
> > +}
> > +
> > +static void virtblk_cleanup_reqs(struct virtio_blk *vblk) {
> > + struct virtio_blk_vq *blk_vq;
> > + struct request_queue *q;
> > + struct virtqueue *vq;
> > + unsigned long flags;
> > + int i;
> > +
> > + vq = vblk->vqs[0].vq;
> > + if (!virtqueue_is_broken(vq))
> > + return;
> > +
> > + q = vblk->disk->queue;
> > + /* Block upper layer to not get any new requests */
> > + blk_mq_quiesce_queue(q);
> > +
> > + for (i = 0; i < vblk->num_vqs; i++) {
> > + blk_vq = &vblk->vqs[i];
> > +
> > + /* Synchronize with any ongoing virtblk_poll() which may be
> > + * completing the requests to uppper layer which has already
> > + * crossed the broken vq check.
> > + */
> > + spin_lock_irqsave(&blk_vq->lock, flags);
> > + spin_unlock_irqrestore(&blk_vq->lock, flags);
> > + }
> > +
> > + blk_sync_queue(q);
> > +
> > + /* Complete remaining pending requests with error */
> > + blk_mq_tagset_busy_iter(&vblk->tag_set, virtblk_cancel_request,
> > +vblk);
>
> Interrupts can still occur here. What prevents the race between
> virtblk_cancel_request() and virtblk_request_done()?
>
The PCI device which generates the interrupt is already removed so interrupt shouldn't arrive when executing cancel_request.
(This is ignoring the race that Ming pointed out. I am preparing the v1 that eliminates such condition.)
If there was ongoing virtblk_request_done() is synchronized by the for loop above.
> > + blk_mq_tagset_wait_completed_request(&vblk->tag_set);
> > +
> > + /*
> > + * Unblock any pending dispatch I/Os before we destroy device. From
> > + * del_gendisk() -> __blk_mark_disk_dead(disk) will set GD_DEAD
> flag,
> > + * that will make sure any new I/O from bio_queue_enter() to fail.
> > + */
> > + blk_mq_unquiesce_queue(q);
> > +}
> > +
> > static void virtblk_remove(struct virtio_device *vdev) {
> > struct virtio_blk *vblk = vdev->priv;
> >
> > + virtblk_cleanup_reqs(vblk);
> > +
> > /* Make sure no work handler is accessing the device. */
> > flush_work(&vblk->config_work);
> >
> > --
> > 2.34.1
> >
