> Hi Dmitry, > Thank you for your review and the comment. > > On 21/05/2026 22:01, Dmitry Osipenko wrote: >> 21.05.2026 05:19, Ryosuke Yasuoka пишет: >>> virtio_gpu_queue_ctrl_sgs() and virtio_gpu_queue_cursor() use >>> wait_event() without any abort condition when waiting for virtqueue >>> space. If the host device stops processing commands, these waits block >>> indefinitely inside a drm_dev_enter/exit() critical section. Since >>> drm_dev_unplug(), which is called in device removal and system shutdown >>> call path, blocks on synchronize_srcu() until all critical sections >>> complete, device removal and system shutdown also hang. >>> >>> Add a vqs_released flag to virtio_gpu_device and include it in the >>> wait_event() condition. Set the flag and wake up both queues in a new >>> virtio_gpu_release_vqs() helper, called before drm_dev_unplug() in both >>> virtio_gpu_remove() and virtio_gpu_shutdown(). When the flag is set, the >>> wait returns immediately and the command is aborted, following the same >>> cleanup path as drm_dev_enter() failure. >>> >>> Reported-by: >>> syzbot+d6dd6f86d3aaf7eebe7406e45c1c6e549453f...@syzkaller.appspotmail.com >>> Closes: >>> https://syzkaller.appspot.com/bug?id=d6dd6f86d3aaf7eebe7406e45c1c6e549453f224 >>> Reported-by: >>> syzbot+908bd910da5dd79b88de4cf7baf376cc873a9...@syzkaller.appspotmail.com >>> Closes: >>> https://syzkaller.appspot.com/bug?id=908bd910da5dd79b88de4cf7baf376cc873a922e >>> Signed-off-by: Ryosuke Yasuoka <[email protected]> >>> --- >>> Changes in v2: >>> - Update the commit message. >>> - Replace wait_event_timeout() with wait_event() using a compound >>> condition that includes a new vqs_released flag. >>> - Add virtio_gpu_release_vqs() helper to set the flag and wake up >>> both queues, called before drm_dev_unplug() in remove and shutdown >>> paths. >>> - Remove the hardcoded 5-second timeout. Recovery is now driven by >>> the driver flag instead of an arbitrary timeout value. >>> --- >>> drivers/gpu/drm/virtio/virtgpu_drv.c | 15 +++++++++++++++ >>> drivers/gpu/drm/virtio/virtgpu_drv.h | 1 + >>> drivers/gpu/drm/virtio/virtgpu_vq.c | 23 +++++++++++++++++++++-- >>> 3 files changed, 37 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c >>> b/drivers/gpu/drm/virtio/virtgpu_drv.c >>> index a5ce96fb8a1d..e4fe5e0780f9 100644 >>> --- a/drivers/gpu/drm/virtio/virtgpu_drv.c >>> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c >>> @@ -119,10 +119,24 @@ static int virtio_gpu_probe(struct virtio_device >>> *vdev) >>> return ret; >>> } >>> >>> +/* >>> + * Release pending virtqueue waits so the drm_dev_enter/exit() critical >>> + * sections complete before drm_dev_unplug() blocks on synchronize_srcu(). >>> + */ >>> +static void virtio_gpu_release_vqs(struct drm_device *dev) >>> +{ >>> + struct virtio_gpu_device *vgdev = dev->dev_private; >>> + >>> + vgdev->vqs_released = true; >>> + wake_up_all(&vgdev->ctrlq.ack_queue); >>> + wake_up_all(&vgdev->cursorq.ack_queue); >>> +} >>> + >>> static void virtio_gpu_remove(struct virtio_device *vdev) >>> { >>> struct drm_device *dev = vdev->priv; >>> >>> + virtio_gpu_release_vqs(dev); >>> drm_dev_unplug(dev); >>> drm_atomic_helper_shutdown(dev); >>> virtio_gpu_deinit(dev); >>> @@ -133,6 +147,7 @@ static void virtio_gpu_shutdown(struct virtio_device >>> *vdev) >>> { >>> struct drm_device *dev = vdev->priv; >>> >>> + virtio_gpu_release_vqs(dev); >>> /* stop talking to the device */ >>> drm_dev_unplug(dev); >>> } >>> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h >>> b/drivers/gpu/drm/virtio/virtgpu_drv.h >>> index f17660a71a3e..0bd69a40857e 100644 >>> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h >>> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h >>> @@ -235,6 +235,7 @@ struct virtio_gpu_device { >>> >>> struct virtio_gpu_queue ctrlq; >>> struct virtio_gpu_queue cursorq; >>> + bool vqs_released; >>> struct kmem_cache *vbufs; >>> >>> atomic_t pending_commands; >>> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c >>> b/drivers/gpu/drm/virtio/virtgpu_vq.c >>> index 67865810a2e7..8057a9b7356d 100644 >>> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c >>> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c >>> @@ -396,7 +396,19 @@ 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); >>> + wait_event(vgdev->ctrlq.ack_queue, >>> + vq->num_free >= elemcnt || vgdev->vqs_released); >>> + /* >>> + * Set by virtio_gpu_release_vqs() to unblock >>> + * synchronize_srcu() wait in drm_dev_unplug(). >>> + */ >>> + if (vgdev->vqs_released) { >>> + 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 +578,14 @@ 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); >>> + wait_event(vgdev->cursorq.ack_queue, >>> + vq->num_free >= outcnt || vgdev->vqs_released); >>> + /* See comment in virtio_gpu_queue_ctrl_sgs(). */ >>> + if (vgdev->vqs_released) { >>> + free_vbuf(vgdev, vbuf); >>> + drm_dev_exit(idx); >>> + return; >>> + } >>> spin_lock(&vgdev->cursorq.qlock); >>> goto retry; >>> } else { >> >> What about other wait_event in the driver? Why only these? > > There are other wait_event() calls on vgdev->resp_wq in virtgpu_prime.c > and virtgpu_vram.c. These can also cause a stuck process when the host > device stops or does not respond and should be fixed. However, they are > not related to the issue being fixed here. I think they should be > addressed in a separate commit. > > The wait_event(vgdev->resp_wq) calls wait for a host response, not for > virtqueue ring space. They are not inside a drm_dev_enter/exit() > critical section, so they don't block drm_dev_unplug() -> > synchronize_srcu() and are not part of the deadlock reported by syzbot. > > However, if a process is stuck in wait_event(vgdev->resp_wq), there is > no way to recover other than host device recovery itself. We can still > remove the device and destroy the virtqueues while the process is stuck, > so the host response can never arrive. IIUC, the stuck thread holds a > drm_device reference, preventing vgdev from being freed; this is a > resource leak. > > This can be fixed by adding a wake_up_all() and a vqs_released check > similar to what is done for ctrlq/cursorq. However, I think this should > be a separate commit since the root cause and problem are different. > > Alternatively, the resp_wq wait_event() calls could be converted to > wait_event_interruptible() to fix the issue. But as you mentioned > earlier in the v1 comment, we need the wait_event_interruptible() > rework. > > What do you think? Should I include the resp_wq fix as a separate commit > in this patch series, or leave it for the _interruptible() rework? > > Best regards, > Ryosuke > >
I see the command but can't find the corresponding bug. The email is sent to [email protected] address but the HASH does not correspond to any known bug. Please double check the address.
