On Wed, Jun 25, 2025 at 07:08:54PM +0000, Parav Pandit wrote:
>
> > From: Michael S. Tsirkin <m...@redhat.com>
> > Sent: 25 June 2025 05:15 PM
> >
> > On Wed, Jun 25, 2025 at 11:08:42AM +0000, Parav Pandit wrote:
> > >
> > > > From: Michael S. Tsirkin <m...@redhat.com>
> > > > Sent: 25 June 2025 04:34 PM
> > > >
> > > > On Wed, Jun 25, 2025 at 02:55:27AM +0000, Parav Pandit wrote:
> > > > >
> > > > > > From: Michael S. Tsirkin <m...@redhat.com>
> > > > > > Sent: 25 June 2025 01:24 AM
> > > > > >
> > > > > > On Tue, Jun 24, 2025 at 07:11:29PM +0000, Parav Pandit wrote:
> > > > > > >
> > > > > > >
> > > > > > > > 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_que
> > > > > > > > > > ue_r
> > > > > > > > > > eset
> > > > > > > > > > ()
> > > > > > > > > >
> > > > > > > > > > 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.
> > > > > >
> > > > > > This one is kind of pointless then? It just fixes the specific
> > > > > > race window that your test harness happens to hit?
> > > > > >
> > > > > It was reported by Li from Baidu, whose tests failed.
> > > > > I missed to tag "reported-by" in v5. I had it until v4. :(
> > > > >
> > > > > > Maybe it's better to wait until someone does a comprehensive fix..
> > > > > >
> > > > > >
> > > > > Oh, I was under impression is that you wanted to step forward in
> > > > > discussion
> > > > of v4.
> > > > > If you prefer a comprehensive support across layers of virtio, I
> > > > > suggest you
> > > > should revert the cited patch in fixes tag.
> > > > >
> > > > > Otherwise, it is in degraded state as virtio never supported surprise
> > removal.
> > > > > By reverting the cited patch (or with this fix), the requests and
> > > > > disk deletion
> > > > will not hang.
> > > >
> > > > But they will hung in virtio core on reset, will they not? The tests
> > > > just do not happen to trigger this?
> > > >
> > > It will hang if it a true surprise removal which no device did so far
> > > because it
> > never worked.
> > > (or did, but always hung that no one reported yet)
> > >
> > > I am familiar with 2 or more PCI devices who reports surprise removal,
> > which do not complete the requests but yet allows device reset flow.
> > > This is because device is still there on the PCI bus. Only via side band
> > > signals
> > device removal was reported.
> >
> > So why do we care about it so much? I think it's great this patch exists,
> > for
> > example it makes it easier to test surprise removal and find more bugs. But
> > is
> > it better to just have it hang unconditionally? Are we now making a
> > commitment that it's working - one we don't seem to intend to implement?
> >
> The patch improves the situation from its current state.
> But as you posted, more changes in pci layer are needed.
> I didn't audit where else it may be needed.
>
> vp_reset() may need to return the status back of successful/failure reset.
> Otherwise during probe(), vp_reset() aborts the reset and attempts to load
> the driver for removed device.
yes however this is not at all different that hotunplug right after
reset.
> I guess suspend() callback also infinitely waits during freezing the queue
> also needs adaptation.
Which callback is that I don't understand.
> > > But I agree that for full support, virtio all layer changes would be
> > > needed as
> > new functionality (without fixes tag :) ).
> >
> >
> > Or with a fixes tag - lots of people just use it as a signal to mean "where
> > can
> > this be reasonably backported to".
> >
> Yes, I think the fix for the older kernels is needed, hence I cced stable too.
>
> >
> > > > > Please let me know if I should re-send to revert the patch listed in
> > > > > fixes
> > tag.
> > > > >
> > > > > > > > > > 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/c45dd68698cd472
> > > > > > > > > > > 38c5
> > > > > > > > > > > 5fb7
> > > > > > > > > > > 3ca9
> > > > > > > > > > > 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
> > > > > > > > > > >
