2022-12-26 07:53:27

by Jason Wang

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

Switch to reuse BAD_RING() to allow common logic to be implemented in
BAD_RING().

Signed-off-by: Jason Wang <[email protected]>
---
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

2022-12-27 00:10:58

by Michael S. Tsirkin

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

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 <[email protected]>
> ---
> 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

2022-12-27 04:06:36

by Jason Wang

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

On Tue, Dec 27, 2022 at 7:36 AM Michael S. Tsirkin <[email protected]> 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 <[email protected]>
> > ---
> > 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 <[email protected]>
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
>

2022-12-27 08:01:45

by Michael S. Tsirkin

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

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 <[email protected]> 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 <[email protected]>
> > > ---
> > > 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 <[email protected]>
> 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
> >