[PATCH] drm/virtio: add timeout to virtqueue wait to avoid hung task

[PATCH] drm/virtio: add timeout to virtqueue wait to avoid hung task

[Ryosuke Yasuoka]

virtio_gpu_queue_ctrl_sgs() and virtio_gpu_queue_cursor() use
wait_event() without timeout when waiting for virtqueue space. If the
host device stops processing commands, these waits block indefinitely.
Since callers may hold DRM locks, this can make the entire system
unresponsive.

Replace wait_event() with wait_event_timeout() using a 5-second timeout,
consistent with the existing timeout pattern in the driver. On timeout,
clean up and return -ENODEV, following the same error path as
drm_dev_enter() failure.

Reported-by: syzbot+d6dd6f86d3aaf7eebe7406e45c1c6e549453f224@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=d6dd6f86d3aaf7eebe7406e45c1c6e549453f224
Reported-by: syzbot+908bd910da5dd79b88de4cf7baf376cc873a922e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=908bd910da5dd79b88de4cf7baf376cc873a922e
Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
---
 drivers/gpu/drm/virtio/virtgpu_vq.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 67865810a2e7..05e816a0ae0b 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -396,7 +396,16 @@ static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
 	if (vq->num_free < elemcnt) {
 		spin_unlock(&vgdev->ctrlq.qlock);
 		virtio_gpu_notify(vgdev);
-		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= elemcnt);
+		if (!wait_event_timeout(vgdev->ctrlq.ack_queue,
+					vq->num_free >= elemcnt,
+					5 * HZ)) {
+			/* The device did not respond */
+			if (fence && vbuf->objs)
+				virtio_gpu_array_unlock_resv(vbuf->objs);
+			free_vbuf(vgdev, vbuf);
+			drm_dev_exit(idx);
+			return -ENODEV;
+		}
 		goto again;
 	}
 
@@ -566,7 +575,14 @@ static void virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
 	ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
 	if (ret == -ENOSPC) {
 		spin_unlock(&vgdev->cursorq.qlock);
-		wait_event(vgdev->cursorq.ack_queue, vq->num_free >= outcnt);
+		if (!wait_event_timeout(vgdev->cursorq.ack_queue,
+					vq->num_free >= outcnt,
+					5 * HZ)) {
+			/* The device did not respond */
+			free_vbuf(vgdev, vbuf);
+			drm_dev_exit(idx);
+			return;
+		}
 		spin_lock(&vgdev->cursorq.qlock);
 		goto retry;
 	} else {

---
base-commit: 5d6919055dec134de3c40167a490f33c74c12581
change-id: 20260512-virtio-gpu_wait_event-e0cdf8675b7c

Best regards,
-- 
Ryosuke Yasuoka <ryasuoka@redhat.com>

Re: [PATCH] drm/virtio: add timeout to virtqueue wait to avoid hung task

[syzbot]

> virtio_gpu_queue_ctrl_sgs() and virtio_gpu_queue_cursor() use
> wait_event() without timeout when waiting for virtqueue space. If the
> host device stops processing commands, these waits block indefinitely.
> Since callers may hold DRM locks, this can make the entire system
> unresponsive.
>
> Replace wait_event() with wait_event_timeout() using a 5-second timeout,
> consistent with the existing timeout pattern in the driver. On timeout,
> clean up and return -ENODEV, following the same error path as
> drm_dev_enter() failure.
>
> Reported-by: syzbot+d6dd6f86d3aaf7eebe7406e45c1c6e549453f224@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?id=d6dd6f86d3aaf7eebe7406e45c1c6e549453f224
> Reported-by: syzbot+908bd910da5dd79b88de4cf7baf376cc873a922e@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?id=908bd910da5dd79b88de4cf7baf376cc873a922e
> Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_vq.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> index 67865810a2e7..05e816a0ae0b 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> @@ -396,7 +396,16 @@ static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
>  	if (vq->num_free < elemcnt) {
>  		spin_unlock(&vgdev->ctrlq.qlock);
>  		virtio_gpu_notify(vgdev);
> -		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= elemcnt);
> +		if (!wait_event_timeout(vgdev->ctrlq.ack_queue,
> +					vq->num_free >= elemcnt,
> +					5 * HZ)) {
> +			/* The device did not respond */
> +			if (fence && vbuf->objs)
> +				virtio_gpu_array_unlock_resv(vbuf->objs);
> +			free_vbuf(vgdev, vbuf);
> +			drm_dev_exit(idx);
> +			return -ENODEV;
> +		}
>  		goto again;
>  	}
>  
> @@ -566,7 +575,14 @@ static void virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
>  	ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
>  	if (ret == -ENOSPC) {
>  		spin_unlock(&vgdev->cursorq.qlock);
> -		wait_event(vgdev->cursorq.ack_queue, vq->num_free >= outcnt);
> +		if (!wait_event_timeout(vgdev->cursorq.ack_queue,
> +					vq->num_free >= outcnt,
> +					5 * HZ)) {
> +			/* The device did not respond */
> +			free_vbuf(vgdev, vbuf);
> +			drm_dev_exit(idx);
> +			return;
> +		}
>  		spin_lock(&vgdev->cursorq.qlock);
>  		goto retry;
>  	} else {
>
> ---
> base-commit: 5d6919055dec134de3c40167a490f33c74c12581
> change-id: 20260512-virtio-gpu_wait_event-e0cdf8675b7c
>
> Best regards,
> -- 
> Ryosuke Yasuoka <ryasuoka@redhat.com>
>

I see the command but can't find the corresponding bug.
The email is sent to  syzbot+HASH@syzkaller.appspotmail.com address
but the HASH does not correspond to any known bug.
Please double check the address.

Re: [PATCH] drm/virtio: add timeout to virtqueue wait to avoid hung task

[syzbot]

> virtio_gpu_queue_ctrl_sgs() and virtio_gpu_queue_cursor() use
> wait_event() without timeout when waiting for virtqueue space. If the
> host device stops processing commands, these waits block indefinitely.
> Since callers may hold DRM locks, this can make the entire system
> unresponsive.
>
> Replace wait_event() with wait_event_timeout() using a 5-second timeout,
> consistent with the existing timeout pattern in the driver. On timeout,
> clean up and return -ENODEV, following the same error path as
> drm_dev_enter() failure.
>
> Reported-by: syzbot+d6dd6f86d3aaf7eebe7406e45c1c6e549453f224@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?id=d6dd6f86d3aaf7eebe7406e45c1c6e549453f224
> Reported-by: syzbot+908bd910da5dd79b88de4cf7baf376cc873a922e@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?id=908bd910da5dd79b88de4cf7baf376cc873a922e
> Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_vq.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> index 67865810a2e7..05e816a0ae0b 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> @@ -396,7 +396,16 @@ static int virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
>  	if (vq->num_free < elemcnt) {
>  		spin_unlock(&vgdev->ctrlq.qlock);
>  		virtio_gpu_notify(vgdev);
> -		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= elemcnt);
> +		if (!wait_event_timeout(vgdev->ctrlq.ack_queue,
> +					vq->num_free >= elemcnt,
> +					5 * HZ)) {
> +			/* The device did not respond */
> +			if (fence && vbuf->objs)
> +				virtio_gpu_array_unlock_resv(vbuf->objs);
> +			free_vbuf(vgdev, vbuf);
> +			drm_dev_exit(idx);
> +			return -ENODEV;
> +		}
>  		goto again;
>  	}
>  
> @@ -566,7 +575,14 @@ static void virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
>  	ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
>  	if (ret == -ENOSPC) {
>  		spin_unlock(&vgdev->cursorq.qlock);
> -		wait_event(vgdev->cursorq.ack_queue, vq->num_free >= outcnt);
> +		if (!wait_event_timeout(vgdev->cursorq.ack_queue,
> +					vq->num_free >= outcnt,
> +					5 * HZ)) {
> +			/* The device did not respond */
> +			free_vbuf(vgdev, vbuf);
> +			drm_dev_exit(idx);
> +			return;
> +		}
>  		spin_lock(&vgdev->cursorq.qlock);
>  		goto retry;
>  	} else {
>
> ---
> base-commit: 5d6919055dec134de3c40167a490f33c74c12581
> change-id: 20260512-virtio-gpu_wait_event-e0cdf8675b7c
>
> Best regards,
> -- 
> Ryosuke Yasuoka <ryasuoka@redhat.com>
>

I see the command but can't find the corresponding bug.
The email is sent to  syzbot+HASH@syzkaller.appspotmail.com address
but the HASH does not correspond to any known bug.
Please double check the address.