> From: Michael S. Tsirkin <m...@redhat.com> > Sent: 26 June 2025 11:34 AM > > On Thu, Jun 26, 2025 at 03:26:12AM +0000, Parav Pandit wrote: > > > > > > > From: Michael S. Tsirkin <m...@redhat.com> > > > Sent: 26 June 2025 12:52 AM > > > > > > 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. > > > > > For hotunplug after reset, we likely need a timeout handler. > > Because block driver running inside the remove() callback waiting for the > > IO, > may not get notified from driver core to synchronize ongoing remove(). > > > Notified of what? Notification that surprise-removal occurred.
> So is the scenario that graceful remove starts, and > meanwhile a surprise removal happens? > Right. > > > > > > I guess suspend() callback also infinitely waits during freezing > > > > the queue > > > also needs adaptation. > > > > > > Which callback is that I don't understand. > > virtblk_freeze() at [1]. > > > > [1] > > https://elixir.bootlin.com/linux/v6.15.3/source/drivers/block/virtio_b > > lk.c#L1622 > > > > > > > > > > > > > > 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/c45dd68 > > > > > > > > > > > > > > 698c > > > > > > > > > > > > > > d472 > > > > > > > > > > > > > > 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->t > > > > > > > > > > > > > > +ag_s > > > > > > > > > > > > > > +et); > > > > > > > > > > > > > > + > > > > > > > > > > > > > > + /* > > > > > > > > > > > > > > + * 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 > > > > > > > > > > > > > >
