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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" 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 --- changelog: v2->v3: - updated commit log v1->v2: - updated commit log to describe WRITE_ONCE usages v0->v1: - removed fixes tag from commit log - using WRITE_ONCE() as its enough for smp cache coherency as well as undesired compiler optimization --- drivers/virtio/virtio_ring.c | 6 ++++-- 1 file 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); -- 2.27.0 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization