virtio-blk: don't keep queue frozen during system suspend

Commit 4ce6e2db00de ("virtio-blk: Ensure no requests in virtqueues before
deleting vqs.") replaces queue quiesce with queue freeze in virtio-blk's
PM callbacks. And the motivation is to drain inflight IOs before suspending.

block layer's queue freeze looks very handy, but it is also easy to cause
deadlock, such as, any attempt to call into bio_queue_enter() may run into
deadlock if the queue is frozen in current context. There are all kinds
of ->suspend() called in suspend context, so keeping queue frozen in the
whole suspend context isn't one good idea. And Marek reported lockdep
warning[1] caused by virtio-blk's freeze queue in virtblk_freeze().

[1] https://lore.kernel.org/linux-block/ca16370e-d646-4eee-b9cc-87277c89c43c@samsung.com/

Given the motivation is to drain in-flight IOs, it can be done by calling
freeze & unfreeze, meantime restore to previous behavior by keeping queue
quiesced during suspend.

Cc: Yi Sun <yi.sun@unisoc.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: virtualization@lists.linux.dev
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20241112125821.1475793-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index c0cdba71f43640ccff96d83f9e63620bebdda2ab..3efe378f138662b9220d54d31badf4fad6e1a0d5 100644 (file)
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1586,9 +1586,12 @@ static void virtblk_remove(struct virtio_device *vdev)
 static int virtblk_freeze(struct virtio_device *vdev)
 {
        struct virtio_blk *vblk = vdev->priv;
+       struct request_queue *q = vblk->disk->queue;
 
        /* Ensure no requests in virtqueues before deleting vqs. */
-       blk_mq_freeze_queue(vblk->disk->queue);
+       blk_mq_freeze_queue(q);
+       blk_mq_quiesce_queue_nowait(q);
+       blk_mq_unfreeze_queue(q);
 
        /* Ensure we don't receive any more interrupts */
        virtio_reset_device(vdev);
@@ -1612,8 +1615,8 @@ static int virtblk_restore(struct virtio_device *vdev)
                return ret;
 
        virtio_device_ready(vdev);
+       blk_mq_unquiesce_queue(vblk->disk->queue);
 
-       blk_mq_unfreeze_queue(vblk->disk->queue);
        return 0;
 }
 #endif