diff options
| author | Parav Pandit <parav@nvidia.com> | 2021-07-21 17:26:45 +0300 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2021-08-10 11:50:54 -0400 |
| commit | 60f0779862e4ab943810187752c462e85f5fa371 (patch) | |
| tree | 27575f63cc1973c87b8be9a32db44f20ba069df7 | |
| parent | 36a21d51725af2ce0700c6ebcb6b9594aac658a6 (diff) | |
virtio: Improve vq->broken access to avoid any compiler optimization
Currently vq->broken field is read by virtqueue_is_broken() in busy
loop in one context by virtnet_send_command().
vq->broken is set to true in other process context by
virtio_break_device(). Reader and writer are accessing it without any
synchronization. This may lead to a compiler optimization which may
result to optimize reading vq->broken only once.
Hence, force reading vq->broken on each invocation of
virtqueue_is_broken() and also force writing it so that such
update is visible to the readers.
It is a theoretical fix that isn't yet encountered in the field.
Signed-off-by: Parav Pandit <parav@nvidia.com>
Link: https://lore.kernel.org/r/20210721142648.1525924-2-parav@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
| -rw-r--r-- | drivers/virtio/virtio_ring.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 89bfe46a8a7f..e179c7c7622c 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -2373,7 +2373,7 @@ bool virtqueue_is_broken(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); - return vq->broken; + return READ_ONCE(vq->broken); } EXPORT_SYMBOL_GPL(virtqueue_is_broken); @@ -2387,7 +2387,9 @@ void virtio_break_device(struct virtio_device *dev) list_for_each_entry(_vq, &dev->vqs, list) { struct vring_virtqueue *vq = to_vvq(_vq); - vq->broken = true; + + /* Pairs with READ_ONCE() in virtqueue_is_broken(). */ + WRITE_ONCE(vq->broken, true); } } EXPORT_SYMBOL_GPL(virtio_break_device); |