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authorParav Pandit <parav@nvidia.com>2021-07-21 17:26:45 +0300
committerMichael S. Tsirkin <mst@redhat.com>2021-08-10 18:50:54 +0300
commit60f0779862e4ab943810187752c462e85f5fa371 (patch)
tree27575f63cc1973c87b8be9a32db44f20ba069df7 /drivers/virtio
parent36a21d51725af2ce0700c6ebcb6b9594aac658a6 (diff)
downloadlinux-60f0779862e4ab943810187752c462e85f5fa371.tar.xz
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>
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c6
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);