Re: [PATCH] virtio_blk: Fix device surprise removal

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Feb 22, 2024 at 04:46:38AM +0000, Parav Pandit wrote:
> 
> 
> > From: Stefan Hajnoczi <stefanha@redhat.com>
> > Sent: Wednesday, February 21, 2024 3:35 AM
> > To: Parav Pandit <parav@nvidia.com>
> > 
> > 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@vger.kernel.org
> > > Reported-by: lirongqing@baidu.com
> > > Closes:
> > > https://lore.kernel.org/virtualization/c45dd68698cd47238c55fb73ca9b474
> > > 1@baidu.com/
> > > Co-developed-by: Chaitanya Kulkarni <kch@nvidia.com>
> > > Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
> > > Signed-off-by: Parav Pandit <parav@nvidia.com>
> > > ---
> > >  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.
> 

Yes, this works, but I feel this is very subtle. This is why I am asking
whether we should instead call virtio_synchronize_cbs and then just
invoke all the callbacks one last time from virtio core? 


> > > +	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
> > >