* [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv()
@ 2026-09-12 8:52 Cong Zhang
2026-09-12 9:09 ` Michael S. Tsirkin
2026-09-12 9:19 ` Cong Zhang
0 siblings, 2 replies; 3+ messages in thread
From: Cong Zhang @ 2026-09-12 8:52 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang, Eugenio Pérez, Xuan Zhuo,
Paolo Bonzini, Stefan Hajnoczi, Jens Axboe, Ming Lei
Cc: linux-arm-msm, virtualization, linux-block, linux-kernel, stable,
Cong Zhang
Replace blk_mq_quiesce_queue_nowait() with blk_mq_quiesce_queue() in
virtblk_freeze_priv().
Keep the existing freeze and unfreeze order. The synchronous call waits
for dispatch code that was already running. The queue remains quiesced
until virtblk_restore_priv() calls blk_mq_unquiesce_queue().
Fixes: 7678abee0867 ("virtio-blk: don't keep queue frozen during system suspend")
Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>
---
blk_mq_run_work_fn() can call blk_mq_sched_dispatch_requests() through
blk_mq_run_dispatch_ops(). The dispatcher checks QUEUE_FLAG_QUIESCED
while the flag is clear. It can then be preempted before it gets a
request. At that time, it has no queue usage reference, so
blk_mq_freeze_queue() does not wait for it.
virtblk_freeze_priv() then calls blk_mq_quiesce_queue_nowait() and
blk_mq_unfreeze_queue(). A new request can enter the queue. The old
dispatcher can run again, use its old flag check, get the new request,
and call virtio_queue_rq(). At the same time, virtblk_freeze_priv() can
reset the device, delete the virtqueues, and free vblk->vqs. The old
dispatcher can then use a deleted virtqueue or a NULL vblk->vqs, and the
kernel can crash.
---
Changes in v2:
- Cc stable@vger.kernel.org.
- Link to v1: https://lore.kernel.org/20260911-virtblk_sync_quiesce-v1-1-a883f8f31258@oss.qualcomm.com
---
drivers/block/virtio_blk.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 32bf3ba07a9d..7a570591e040 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1595,7 +1595,7 @@ static int virtblk_freeze_priv(struct virtio_device *vdev)
/* Ensure no requests in virtqueues before deleting vqs. */
memflags = blk_mq_freeze_queue(q);
- blk_mq_quiesce_queue_nowait(q);
+ blk_mq_quiesce_queue(q);
blk_mq_unfreeze_queue(q, memflags);
/* Ensure we don't receive any more interrupts */
---
base-commit: 50d05c7c76c96b90462f24debacca971d2e86713
change-id: 20260910-virtblk_sync_quiesce-9b2c88d45416
Best regards,
--
Cong Zhang <cong.zhang@oss.qualcomm.com>
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv()
2026-09-12 8:52 [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv() Cong Zhang
@ 2026-09-12 9:09 ` Michael S. Tsirkin
2026-09-12 9:19 ` Cong Zhang
1 sibling, 0 replies; 3+ messages in thread
From: Michael S. Tsirkin @ 2026-09-12 9:09 UTC (permalink / raw)
To: Cong Zhang
Cc: Jason Wang, Eugenio Pérez, Xuan Zhuo, Paolo Bonzini,
Stefan Hajnoczi, Jens Axboe, Ming Lei, linux-arm-msm,
virtualization, linux-block, linux-kernel, stable
On Sat, Sep 12, 2026 at 04:52:44PM +0800, Cong Zhang wrote:
> Replace blk_mq_quiesce_queue_nowait() with blk_mq_quiesce_queue() in
> virtblk_freeze_priv().
>
> Keep the existing freeze and unfreeze order. The synchronous call waits
> for dispatch code that was already running. The queue remains quiesced
> until virtblk_restore_priv() calls blk_mq_unquiesce_queue().
This repeatition of the code in english is not what we need
in the commit log.
Suggested format:
The following issue was observed by ...: currently .... because ... this is a
problem because ... and we can not ... because ... to fix ... so that
... tested by ...: before ... after ...
> Fixes: 7678abee0867 ("virtio-blk: don't keep queue frozen during system suspend")
>
> Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>
no empty lines between tags please
> ---
> blk_mq_run_work_fn() can call blk_mq_sched_dispatch_requests() through
> blk_mq_run_dispatch_ops(). The dispatcher checks QUEUE_FLAG_QUIESCED
> while the flag is clear. It can then be preempted before it gets a
> request. At that time, it has no queue usage reference, so
> blk_mq_freeze_queue() does not wait for it.
>
> virtblk_freeze_priv() then calls blk_mq_quiesce_queue_nowait() and
> blk_mq_unfreeze_queue(). A new request can enter the queue. The old
> dispatcher can run again, use its old flag check, get the new request,
> and call virtio_queue_rq(). At the same time, virtblk_freeze_priv() can
> reset the device, delete the virtqueues, and free vblk->vqs. The old
> dispatcher can then use a deleted virtqueue or a NULL vblk->vqs, and the
> kernel can crash.
this kind of thing belongs in the commit log.
> ---
> Changes in v2:
> - Cc stable@vger.kernel.org.
which is no longer there?
> - Link to v1: https://lore.kernel.org/20260911-virtblk_sync_quiesce-v1-1-a883f8f31258@oss.qualcomm.com
> ---
> drivers/block/virtio_blk.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 32bf3ba07a9d..7a570591e040 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1595,7 +1595,7 @@ static int virtblk_freeze_priv(struct virtio_device *vdev)
>
> /* Ensure no requests in virtqueues before deleting vqs. */
> memflags = blk_mq_freeze_queue(q);
> - blk_mq_quiesce_queue_nowait(q);
> + blk_mq_quiesce_queue(q);
> blk_mq_unfreeze_queue(q, memflags);
>
> /* Ensure we don't receive any more interrupts */
>
> ---
> base-commit: 50d05c7c76c96b90462f24debacca971d2e86713
> change-id: 20260910-virtblk_sync_quiesce-9b2c88d45416
>
> Best regards,
> --
> Cong Zhang <cong.zhang@oss.qualcomm.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv()
2026-09-12 8:52 [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv() Cong Zhang
2026-09-12 9:09 ` Michael S. Tsirkin
@ 2026-09-12 9:19 ` Cong Zhang
1 sibling, 0 replies; 3+ messages in thread
From: Cong Zhang @ 2026-09-12 9:19 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang, Eugenio Pérez, Xuan Zhuo,
Paolo Bonzini, Stefan Hajnoczi, Jens Axboe, Ming Lei
Cc: linux-arm-msm, virtualization, linux-block, linux-kernel, stable
On 9/12/2026 4:52 PM, Cong Zhang wrote:
> Replace blk_mq_quiesce_queue_nowait() with blk_mq_quiesce_queue() in
> virtblk_freeze_priv().
>
> Keep the existing freeze and unfreeze order. The synchronous call waits
> for dispatch code that was already running. The queue remains quiesced
> until virtblk_restore_priv() calls blk_mq_unquiesce_queue().
>
> Fixes: 7678abee0867 ("virtio-blk: don't keep queue frozen during system suspend")
>
> Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>
>
Just noticed that I forget to add the ack tag, sorry about that.
>
> ---
> blk_mq_run_work_fn() can call blk_mq_sched_dispatch_requests() through
> blk_mq_run_dispatch_ops(). The dispatcher checks QUEUE_FLAG_QUIESCED
> while the flag is clear. It can then be preempted before it gets a
> request. At that time, it has no queue usage reference, so
> blk_mq_freeze_queue() does not wait for it.
>
> virtblk_freeze_priv() then calls blk_mq_quiesce_queue_nowait() and
> blk_mq_unfreeze_queue(). A new request can enter the queue. The old
> dispatcher can run again, use its old flag check, get the new request,
> and call virtio_queue_rq(). At the same time, virtblk_freeze_priv() can
> reset the device, delete the virtqueues, and free vblk->vqs. The old
> dispatcher can then use a deleted virtqueue or a NULL vblk->vqs, and the
> kernel can crash.
> ---
> Changes in v2:
> - Cc stable@vger.kernel.org.
> - Link to v1: https://lore.kernel.org/20260911-virtblk_sync_quiesce-v1-1-a883f8f31258@oss.qualcomm.com
> ---
> drivers/block/virtio_blk.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 32bf3ba07a9d..7a570591e040 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1595,7 +1595,7 @@ static int virtblk_freeze_priv(struct virtio_device *vdev)
>
> /* Ensure no requests in virtqueues before deleting vqs. */
> memflags = blk_mq_freeze_queue(q);
> - blk_mq_quiesce_queue_nowait(q);
> + blk_mq_quiesce_queue(q);
> blk_mq_unfreeze_queue(q, memflags);
>
> /* Ensure we don't receive any more interrupts */
>
> ---
> base-commit: 50d05c7c76c96b90462f24debacca971d2e86713
> change-id: 20260910-virtblk_sync_quiesce-9b2c88d45416
>
> Best regards,
> --
> Cong Zhang <cong.zhang@oss.qualcomm.com>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-09-12 8:52 [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv() Cong Zhang
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