virtio_blk: use synchronous quiesce in virtblk_freeze_priv()

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.

Fix this by using blk_mq_quiesce_queue(), which waits for dispatch code
that was already running. Keep the existing freeze and unfreeze order.
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")
Cc: stable@vger.kernel.org
Acked-by: Jason Wang <jasowangio@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>
Link: https://lore.kernel.org/20260911-virtblk_sync_quiesce-v1-1-a883f8f31258@oss.qualcomm.com
Link: https://patch.msgid.link/20261103-virtblk_sync_quiesce-v3-1-f40233f9bdd9@oss.qualcomm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions