FAILED: patch "[PATCH] virtio_blk: use synchronous quiesce in virtblk_freeze_priv()" failed to apply to 6.12-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 6c6dec7883f8eb10b326bc9d109a4990c885d949
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109200833-failed-6.12-6c6dec7883f8@kernel.org' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 6c6dec7883f8eb10b326bc9d109a4990c885d949 Mon Sep 17 00:00:00 2001
From: Cong Zhang <cong.zhang@oss.qualcomm.com>
Date: Tue, 3 Nov 2026 18:32:21 +0800
Subject: [PATCH] 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>
---
 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 c8bfbf8435ac7..10ba8b0b863b8 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1596,7 +1596,7 @@ 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 */
-- 
2.53.0