virtio: remove overzealous BUG_ON.

The 'disable_cb' callback is designed as an optimization to tell the host
we don't need callbacks now.  As it is not reliable, the debug check is
overzealous: it can happen on two CPUs at the same time.  Document this.

Even if it were reliable, the virtio_net driver doesn't disable
callbacks on transmit so the START_USE/END_USE debugging reentrance
protection can be easily tripped even on UP.

Thanks to Balaji Rao for the bug report and testing.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
CC: Balaji Rao <balajirrao@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 3 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index aa714028641e..c2fa5c630813 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -214,10 +214,7 @@ static void vring_disable_cb(struct virtqueue *_vq)
 {
         struct vring_virtqueue *vq = to_vvq(_vq);
 
-        START_USE(vq);
-        BUG_ON(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
         vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
-        END_USE(vq);
 }
 
 static bool vring_enable_cb(struct virtqueue *_vq)