diff options
| author | Mark Johnston <markj@FreeBSD.org> | 2025-11-04 14:27:33 +0000 |
|---|---|---|
| committer | Colin Percival <cperciva@FreeBSD.org> | 2025-11-07 15:12:02 -0800 |
| commit | 69c726c150772c36854d38e51b6fd921a04caea5 (patch) | |
| tree | ef59b2ac7adb74ffd63fcc4e1f5af3d798c34b67 | |
| parent | 3447fc070cc205671ac33e1582c023033094de7f (diff) | |
virtio: Fix polling in virtqueue_dequeue()
The access of vq->vq_ring.used->idx needs to be volatile-qualified,
otherwise the compiler may optimize virtqueue_poll() into an infinite
loop if there is no data available upon the first poll.
Prior to commit ad17789a8569 this wasn't a problem since an external
function call after each poll inhibited the optimization.
Approved by: re (cperciva)
PR: 289930
MFC after: 3 days
Sponsored by: Klara, Inc.
Fixes: ad17789a8569 ("virtio: Remove the unused poll method")
(cherry picked from commit f999ffdce3813eb946f10999ccffb8275c324469)
(cherry picked from commit 72c76047541ab6cc0e989a74e8de4d6e6a1a94b6)
| -rw-r--r-- | sys/dev/virtio/virtqueue.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/sys/dev/virtio/virtqueue.c b/sys/dev/virtio/virtqueue.c index cc7a233d60ee..41e01549c8b2 100644 --- a/sys/dev/virtio/virtqueue.c +++ b/sys/dev/virtio/virtqueue.c @@ -580,7 +580,8 @@ virtqueue_dequeue(struct virtqueue *vq, uint32_t *len) void *cookie; uint16_t used_idx, desc_idx; - if (vq->vq_used_cons_idx == vq_htog16(vq, vq->vq_ring.used->idx)) + if (vq->vq_used_cons_idx == + vq_htog16(vq, atomic_load_16(&vq->vq_ring.used->idx))) return (NULL); used_idx = vq->vq_used_cons_idx++ & (vq->vq_nentries - 1); |