linux-kernel - Re: [PATCH V3 7/9] virtio: allow to unbreak virtqueue

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Message-ID: <20220425100349-mutt-send-email-mst@kernel.org>
Date:   Mon, 25 Apr 2022 10:04:55 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, sgarzare@...hat.com,
        eperezma@...hat.com, lulu@...hat.com, tglx@...utronix.de,
        peterz@...radead.org, paulmck@...nel.org, maz@...nel.org,
        pasic@...ux.ibm.com
Subject: Re: [PATCH V3 7/9] virtio: allow to unbreak virtqueue

On Mon, Apr 25, 2022 at 02:44:06PM +0200, Cornelia Huck wrote:
> On Mon, Apr 25 2022, Jason Wang <jasowang@...hat.com> wrote:
> 
> > This patch allows the virtio_break_device() to accept a boolean value
> > then we can unbreak the virtqueue.
> >
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > ---
> >  drivers/char/virtio_console.c              | 2 +-
> >  drivers/crypto/virtio/virtio_crypto_core.c | 2 +-
> >  drivers/s390/virtio/virtio_ccw.c           | 4 ++--
> >  drivers/virtio/virtio_pci_common.c         | 2 +-
> >  drivers/virtio/virtio_ring.c               | 4 ++--
> >  include/linux/virtio.h                     | 2 +-
> >  6 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > index e3c430539a17..afede977f7b3 100644
> > --- a/drivers/char/virtio_console.c
> > +++ b/drivers/char/virtio_console.c
> > @@ -1958,7 +1958,7 @@ static void virtcons_remove(struct virtio_device *vdev)
> >  	spin_unlock_irq(&pdrvdata_lock);
> >  
> >  	/* Device is going away, exit any polling for buffers */
> > -	virtio_break_device(vdev);
> > +	virtio_break_device(vdev, true);
> >  	if (use_multiport(portdev))
> >  		flush_work(&portdev->control_work);
> >  	else
> > diff --git a/drivers/crypto/virtio/virtio_crypto_core.c b/drivers/crypto/virtio/virtio_crypto_core.c
> > index c6f482db0bc0..fd17f3f2e958 100644
> > --- a/drivers/crypto/virtio/virtio_crypto_core.c
> > +++ b/drivers/crypto/virtio/virtio_crypto_core.c
> > @@ -215,7 +215,7 @@ static int virtcrypto_update_status(struct virtio_crypto *vcrypto)
> >  		dev_warn(&vcrypto->vdev->dev,
> >  				"Unknown status bits: 0x%x\n", status);
> >  
> > -		virtio_break_device(vcrypto->vdev);
> > +		virtio_break_device(vcrypto->vdev, true);
> >  		return -EPERM;
> >  	}
> >  
> > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > index c19f07a82d62..9a963f5af5b5 100644
> > --- a/drivers/s390/virtio/virtio_ccw.c
> > +++ b/drivers/s390/virtio/virtio_ccw.c
> > @@ -1211,7 +1211,7 @@ static void virtio_ccw_remove(struct ccw_device *cdev)
> >  
> >  	if (vcdev && cdev->online) {
> >  		if (vcdev->device_lost)
> > -			virtio_break_device(&vcdev->vdev);
> > +			virtio_break_device(&vcdev->vdev, true);
> >  		unregister_virtio_device(&vcdev->vdev);
> >  		spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
> >  		dev_set_drvdata(&cdev->dev, NULL);
> > @@ -1228,7 +1228,7 @@ static int virtio_ccw_offline(struct ccw_device *cdev)
> >  	if (!vcdev)
> >  		return 0;
> >  	if (vcdev->device_lost)
> > -		virtio_break_device(&vcdev->vdev);
> > +		virtio_break_device(&vcdev->vdev, true);
> >  	unregister_virtio_device(&vcdev->vdev);
> >  	spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
> >  	dev_set_drvdata(&cdev->dev, NULL);
> > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > index d724f676608b..39a711ddff30 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -583,7 +583,7 @@ static void virtio_pci_remove(struct pci_dev *pci_dev)
> >  	 * layers can abort any ongoing operation.
> >  	 */
> >  	if (!pci_device_is_present(pci_dev))
> > -		virtio_break_device(&vp_dev->vdev);
> > +		virtio_break_device(&vp_dev->vdev, true);
> >  
> >  	pci_disable_sriov(pci_dev);
> >  
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index cfb028ca238e..6da13495a70c 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -2382,7 +2382,7 @@ EXPORT_SYMBOL_GPL(virtqueue_is_broken);
> >   * This should prevent the device from being used, allowing drivers to
> >   * recover.  You may need to grab appropriate locks to flush.
> >   */
> > -void virtio_break_device(struct virtio_device *dev)
> > +void virtio_break_device(struct virtio_device *dev, bool broken)
> 
> I think we need to be careful to say when it is safe to unset 'broken'.
> 
> The current callers set all queues to broken in case of surprise removal
> (ccw, pci), removal (console), or the device behaving badly
> (crypto). There's also code setting individual queues to broken. We do
> not want to undo any of these, unless the device has gone through a
> reset in the meanwhile. Maybe add:
> 
> "It is only safe to call this function to *remove* the broken flag for a
> device that is (re)transitioning to becoming usable; calling it that way
> during normal usage may have unpredictable consequences."
> 
> (Not sure how to word this; especially if we consider future usage of
> queue reset.)


Right. I would prefer __virtio_unbreak_device or something similar
with a bit comment explaining it's only safe to call during probe.

-- 
MST