* [PATCH v3] virtio_ring: Fix KCSAN warnings in virtqueue_enable_cb_delayed_split()
@ 2026-03-11 17:05 Chaohai Chen
2026-03-12 2:41 ` Jason Wang
0 siblings, 1 reply; 2+ messages in thread
From: Chaohai Chen @ 2026-03-11 17:05 UTC (permalink / raw)
To: mst, jasowang, xuanzhuo, eperezma
Cc: virtualization, linux-kernel, Chaohai Chen
KCSAN warns as follow:
[ 109.277250] ==================================================================
[ 109.283600] BUG: KCSAN: data-race in virtqueue_enable_cb_delayed_split+0x10f/0x170
[ 109.295263] race at unknown origin, with read to 0xffff8b2a92ef2042 of 2 bytes by interrupt on cpu 1:
[ 109.306934] virtqueue_enable_cb_delayed_split+0x10f/0x170
[ 109.312880] virtqueue_enable_cb_delayed+0x3b/0x70
[ 109.318852] start_xmit+0x315/0x860 [virtio_net]
[ 109.324532] dev_hard_start_xmit+0x85/0x380
[ 109.329993] sch_direct_xmit+0xd3/0x680
[ 109.335360] __dev_xmit_skb+0x4ee/0xcc0
[ 109.340568] __dev_queue_xmit+0x560/0xe00
[ 109.345701] ip_finish_output2+0x49a/0x9b0
[ 109.350743] __ip_finish_output+0x131/0x250
[ 109.355789] ip_finish_output+0x28/0x180
[ 109.360712] ip_output+0xa0/0x1c0
[ 109.365479] __ip_queue_xmit+0x68d/0x9e0
[ 109.370156] ip_queue_xmit+0x33/0x40
[ 109.374783] __tcp_transmit_skb+0x1703/0x1970
[ 109.379467] __tcp_send_ack.part.0+0x1bb/0x320
...
[ 109.499585] do_idle+0x7a/0xe0
[ 109.502979] cpu_startup_entry+0x25/0x30
[ 109.506481] start_secondary+0x116/0x150
[ 109.509930] common_startup_64+0x13e/0x141
[ 109.516626] value changed: 0x0029 -> 0x002a
================================================================================
Add READ_ONCE() to fix the warning.
Signed-off-by: Chaohai Chen <wdhh6@aliyun.com>
---
drivers/virtio/virtio_ring.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 335692d41617..ceb026161639 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1112,8 +1112,9 @@ static bool virtqueue_enable_cb_delayed_split(struct vring_virtqueue *vq)
&vring_used_event(&vq->split.vring),
cpu_to_virtio16(vq->vq.vdev, vq->last_used_idx + bufs));
- if (unlikely((u16)(virtio16_to_cpu(vq->vq.vdev, vq->split.vring.used->idx)
- - vq->last_used_idx) > bufs)) {
+ if (unlikely((u16)(virtio16_to_cpu(vq->vq.vdev,
+ READ_ONCE(vq->split.vring.used->idx))
+ - vq->last_used_idx) > bufs)) {
END_USE(vq);
return false;
}
--
2.43.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v3] virtio_ring: Fix KCSAN warnings in virtqueue_enable_cb_delayed_split()
2026-03-11 17:05 [PATCH v3] virtio_ring: Fix KCSAN warnings in virtqueue_enable_cb_delayed_split() Chaohai Chen
@ 2026-03-12 2:41 ` Jason Wang
0 siblings, 0 replies; 2+ messages in thread
From: Jason Wang @ 2026-03-12 2:41 UTC (permalink / raw)
To: Chaohai Chen; +Cc: mst, xuanzhuo, eperezma, virtualization, linux-kernel
On Thu, Mar 12, 2026 at 1:05 AM Chaohai Chen <wdhh6@aliyun.com> wrote:
>
> KCSAN warns as follow:
>
> [ 109.277250] ==================================================================
> [ 109.283600] BUG: KCSAN: data-race in virtqueue_enable_cb_delayed_split+0x10f/0x170
>
> [ 109.295263] race at unknown origin, with read to 0xffff8b2a92ef2042 of 2 bytes by interrupt on cpu 1:
> [ 109.306934] virtqueue_enable_cb_delayed_split+0x10f/0x170
> [ 109.312880] virtqueue_enable_cb_delayed+0x3b/0x70
> [ 109.318852] start_xmit+0x315/0x860 [virtio_net]
> [ 109.324532] dev_hard_start_xmit+0x85/0x380
> [ 109.329993] sch_direct_xmit+0xd3/0x680
> [ 109.335360] __dev_xmit_skb+0x4ee/0xcc0
> [ 109.340568] __dev_queue_xmit+0x560/0xe00
> [ 109.345701] ip_finish_output2+0x49a/0x9b0
> [ 109.350743] __ip_finish_output+0x131/0x250
> [ 109.355789] ip_finish_output+0x28/0x180
> [ 109.360712] ip_output+0xa0/0x1c0
> [ 109.365479] __ip_queue_xmit+0x68d/0x9e0
> [ 109.370156] ip_queue_xmit+0x33/0x40
> [ 109.374783] __tcp_transmit_skb+0x1703/0x1970
> [ 109.379467] __tcp_send_ack.part.0+0x1bb/0x320
> ...
> [ 109.499585] do_idle+0x7a/0xe0
> [ 109.502979] cpu_startup_entry+0x25/0x30
> [ 109.506481] start_secondary+0x116/0x150
> [ 109.509930] common_startup_64+0x13e/0x141
>
> [ 109.516626] value changed: 0x0029 -> 0x002a
> ================================================================================
>
> Add READ_ONCE() to fix the warning.
>
> Signed-off-by: Chaohai Chen <wdhh6@aliyun.com>
Nit: maybe it's better to explain it's a false positive.
Acked-by: Jason Wang <jasowang@redhat.com>
Thanks
> ---
> drivers/virtio/virtio_ring.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 335692d41617..ceb026161639 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1112,8 +1112,9 @@ static bool virtqueue_enable_cb_delayed_split(struct vring_virtqueue *vq)
> &vring_used_event(&vq->split.vring),
> cpu_to_virtio16(vq->vq.vdev, vq->last_used_idx + bufs));
>
> - if (unlikely((u16)(virtio16_to_cpu(vq->vq.vdev, vq->split.vring.used->idx)
> - - vq->last_used_idx) > bufs)) {
> + if (unlikely((u16)(virtio16_to_cpu(vq->vq.vdev,
> + READ_ONCE(vq->split.vring.used->idx))
> + - vq->last_used_idx) > bufs)) {
> END_USE(vq);
> return false;
> }
> --
> 2.43.0
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2026-03-11 17:05 [PATCH v3] virtio_ring: Fix KCSAN warnings in virtqueue_enable_cb_delayed_split() Chaohai Chen
2026-03-12 2:41 ` Jason Wang
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