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[PATCH 2/4] virtio_ring: switch to use BAD_RING()

Jason Wang posted 4 patches 2 years, 8 months ago
There is a newer version of this series
[PATCH 2/4] virtio_ring: switch to use BAD_RING()
Posted by Jason Wang 2 years, 8 months ago 
Switch to reuse BAD_RING() to allow common logic to be implemented in
BAD_RING().

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes since V1:
- switch to use BAD_RING in virtio_break_device()
---
 drivers/virtio/virtio_ring.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 2e7689bb933b..5cfb2fa8abee 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -58,7 +58,8 @@
 	do {							\
 		dev_err(&_vq->vq.vdev->dev,			\
 			"%s:"fmt, (_vq)->vq.name, ##args);	\
-		(_vq)->broken = true;				\
+		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \
+		WRITE_ONCE((_vq)->broken, true);		       \
 	} while (0)
 #define START_USE(vq)
 #define END_USE(vq)
@@ -2237,7 +2238,7 @@ bool virtqueue_notify(struct virtqueue *_vq)
 
 	/* Prod other side to tell it about changes. */
 	if (!vq->notify(_vq)) {
-		vq->broken = true;
+		BAD_RING(vq, "vq %d is broken\n", vq->vq.index);
 		return false;
 	}
 	return true;
@@ -2786,8 +2787,7 @@ void virtio_break_device(struct virtio_device *dev)
 	list_for_each_entry(_vq, &dev->vqs, list) {
 		struct vring_virtqueue *vq = to_vvq(_vq);
 
-		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
-		WRITE_ONCE(vq->broken, true);
+		BAD_RING(vq, "Device break vq %d", _vq->index);
 	}
 	spin_unlock(&dev->vqs_list_lock);
 }
-- 
2.25.1
Re: [PATCH 2/4] virtio_ring: switch to use BAD_RING()
Posted by Michael S. Tsirkin 2 years, 8 months ago 
On Mon, Dec 26, 2022 at 03:49:06PM +0800, Jason Wang wrote:
> Switch to reuse BAD_RING() to allow common logic to be implemented in
> BAD_RING().
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> Changes since V1:
> - switch to use BAD_RING in virtio_break_device()
> ---
>  drivers/virtio/virtio_ring.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 2e7689bb933b..5cfb2fa8abee 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -58,7 +58,8 @@
>  	do {							\
>  		dev_err(&_vq->vq.vdev->dev,			\
>  			"%s:"fmt, (_vq)->vq.name, ##args);	\
> -		(_vq)->broken = true;				\
> +		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \

I don't think WRITE_ONCE/READ_ONCE pair as such. Can you point
me at documentation of such pairing?

> +		WRITE_ONCE((_vq)->broken, true);		       \
>  	} while (0)
>  #define START_USE(vq)
>  #define END_USE(vq)
> @@ -2237,7 +2238,7 @@ bool virtqueue_notify(struct virtqueue *_vq)
>  
>  	/* Prod other side to tell it about changes. */
>  	if (!vq->notify(_vq)) {
> -		vq->broken = true;
> +		BAD_RING(vq, "vq %d is broken\n", vq->vq.index);
>  		return false;
>  	}
>  	return true;
> @@ -2786,8 +2787,7 @@ void virtio_break_device(struct virtio_device *dev)
>  	list_for_each_entry(_vq, &dev->vqs, list) {
>  		struct vring_virtqueue *vq = to_vvq(_vq);
>  
> -		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
> -		WRITE_ONCE(vq->broken, true);
> +		BAD_RING(vq, "Device break vq %d", _vq->index);
>  	}
>  	spin_unlock(&dev->vqs_list_lock);
>  }
> -- 
> 2.25.1
Re: [PATCH 2/4] virtio_ring: switch to use BAD_RING()
Posted by Jason Wang 2 years, 8 months ago 
On Tue, Dec 27, 2022 at 7:36 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Mon, Dec 26, 2022 at 03:49:06PM +0800, Jason Wang wrote:
> > Switch to reuse BAD_RING() to allow common logic to be implemented in
> > BAD_RING().
> >
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > ---
> > Changes since V1:
> > - switch to use BAD_RING in virtio_break_device()
> > ---
> >  drivers/virtio/virtio_ring.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 2e7689bb933b..5cfb2fa8abee 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -58,7 +58,8 @@
> >       do {                                                    \
> >               dev_err(&_vq->vq.vdev->dev,                     \
> >                       "%s:"fmt, (_vq)->vq.name, ##args);      \
> > -             (_vq)->broken = true;                           \
> > +             /* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \
>
> I don't think WRITE_ONCE/READ_ONCE pair as such. Can you point
> me at documentation of such pairing?

Introduced by:

commit 60f0779862e4ab943810187752c462e85f5fa371
Author: Parav Pandit <parav@nvidia.com>
Date:   Wed Jul 21 17:26:45 2021 +0300

    virtio: Improve vq->broken access to avoid any compiler optimization

I think it might still apply here since virtqueue_is_broken() is still
put into a loop inside wait_event().

Thanks

>
> > +             WRITE_ONCE((_vq)->broken, true);                       \
> >       } while (0)
> >  #define START_USE(vq)
> >  #define END_USE(vq)
> > @@ -2237,7 +2238,7 @@ bool virtqueue_notify(struct virtqueue *_vq)
> >
> >       /* Prod other side to tell it about changes. */
> >       if (!vq->notify(_vq)) {
> > -             vq->broken = true;
> > +             BAD_RING(vq, "vq %d is broken\n", vq->vq.index);
> >               return false;
> >       }
> >       return true;
> > @@ -2786,8 +2787,7 @@ void virtio_break_device(struct virtio_device *dev)
> >       list_for_each_entry(_vq, &dev->vqs, list) {
> >               struct vring_virtqueue *vq = to_vvq(_vq);
> >
> > -             /* Pairs with READ_ONCE() in virtqueue_is_broken(). */
> > -             WRITE_ONCE(vq->broken, true);
> > +             BAD_RING(vq, "Device break vq %d", _vq->index);
> >       }
> >       spin_unlock(&dev->vqs_list_lock);
> >  }
> > --
> > 2.25.1
>
Re: [PATCH 2/4] virtio_ring: switch to use BAD_RING()
Posted by Michael S. Tsirkin 2 years, 8 months ago 
On Tue, Dec 27, 2022 at 11:51:02AM +0800, Jason Wang wrote:
> On Tue, Dec 27, 2022 at 7:36 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Dec 26, 2022 at 03:49:06PM +0800, Jason Wang wrote:
> > > Switch to reuse BAD_RING() to allow common logic to be implemented in
> > > BAD_RING().
> > >
> > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > ---
> > > Changes since V1:
> > > - switch to use BAD_RING in virtio_break_device()
> > > ---
> > >  drivers/virtio/virtio_ring.c | 8 ++++----
> > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 2e7689bb933b..5cfb2fa8abee 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -58,7 +58,8 @@
> > >       do {                                                    \
> > >               dev_err(&_vq->vq.vdev->dev,                     \
> > >                       "%s:"fmt, (_vq)->vq.name, ##args);      \
> > > -             (_vq)->broken = true;                           \
> > > +             /* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \
> >
> > I don't think WRITE_ONCE/READ_ONCE pair as such. Can you point
> > me at documentation of such pairing?
> 
> Introduced by:
> 
> commit 60f0779862e4ab943810187752c462e85f5fa371
> Author: Parav Pandit <parav@nvidia.com>
> Date:   Wed Jul 21 17:26:45 2021 +0300
> 
>     virtio: Improve vq->broken access to avoid any compiler optimization
> 
> I think it might still apply here since virtqueue_is_broken() is still
> put into a loop inside wait_event().
> 
> Thanks

Oh I see. Maybe it's a response to some discussion we had at the time,
at this point I can no longer say what it meant.
But you are doing right not changing it here of course.

> >
> > > +             WRITE_ONCE((_vq)->broken, true);                       \
> > >       } while (0)
> > >  #define START_USE(vq)
> > >  #define END_USE(vq)
> > > @@ -2237,7 +2238,7 @@ bool virtqueue_notify(struct virtqueue *_vq)
> > >
> > >       /* Prod other side to tell it about changes. */
> > >       if (!vq->notify(_vq)) {
> > > -             vq->broken = true;
> > > +             BAD_RING(vq, "vq %d is broken\n", vq->vq.index);
> > >               return false;
> > >       }
> > >       return true;
> > > @@ -2786,8 +2787,7 @@ void virtio_break_device(struct virtio_device *dev)
> > >       list_for_each_entry(_vq, &dev->vqs, list) {
> > >               struct vring_virtqueue *vq = to_vvq(_vq);
> > >
> > > -             /* Pairs with READ_ONCE() in virtqueue_is_broken(). */
> > > -             WRITE_ONCE(vq->broken, true);
> > > +             BAD_RING(vq, "Device break vq %d", _vq->index);
> > >       }
> > >       spin_unlock(&dev->vqs_list_lock);
> > >  }
> > > --
> > > 2.25.1
> >

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