[PATCH 1/2] block: move queue quiesce into elevator_change()

[Ming Lei <ming.lei@redhat.com>]

blk_mq_freeze_queue() can't be called on quiesced queue, otherwise it may
never return if there is any queued requests.

Fix it by moving queue quiesce int elevator_change() by adding one flag to
'struct elv_change_ctx' for controlling this behavior.

Fixes: 1e44bedbc921 ("block: unifying elevator change")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-sysfs.c | 5 +----
 block/elevator.c  | 9 +++++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 386374ff655b..8be2390c3c19 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -948,11 +948,8 @@ void blk_unregister_queue(struct gendisk *disk)
 		blk_mq_sysfs_unregister(disk);
 	blk_crypto_sysfs_unregister(disk);
 
-	if (queue_is_mq(q)) {
-		blk_mq_quiesce_queue(q);
+	if (queue_is_mq(q))
 		elevator_set_none(q);
-		blk_mq_unquiesce_queue(q);
-	}
 
 	mutex_lock(&q->sysfs_lock);
 	disk_unregister_independent_access_ranges(disk);
diff --git a/block/elevator.c b/block/elevator.c
index f8d72bd20610..e1386b84a415 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -49,6 +49,7 @@
 struct elv_change_ctx {
 	const char *name;
 	bool no_uevent;
+	bool quiesce_queue;
 
 	/* for unregistering old elevator */
 	struct elevator_queue *old;
@@ -658,12 +659,17 @@ static int elevator_change_done(struct request_queue *q,
  */
 static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 {
+	bool quiesce_queue = ctx->quiesce_queue;
 	unsigned int memflags;
 	int ret = 0;
 
 	lockdep_assert_held(&q->tag_set->update_nr_hwq_lock);
 
+	WARN_ON_ONCE(blk_queue_quiesced(q));
+
 	memflags = blk_mq_freeze_queue(q);
+	if (quiesce_queue)
+		blk_mq_quiesce_queue(q);
 	/*
 	 * May be called before adding disk, when there isn't any FS I/O,
 	 * so freezing queue plus canceling dispatch work is enough to
@@ -678,6 +684,8 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	if (!(q->elevator && elevator_match(q->elevator->type, ctx->name)))
 		ret = elevator_switch(q, ctx);
 	mutex_unlock(&q->elevator_lock);
+	if (quiesce_queue)
+		blk_mq_unquiesce_queue(q);
 	blk_mq_unfreeze_queue(q, memflags);
 	if (!ret)
 		ret = elevator_change_done(q, ctx);
@@ -744,6 +752,7 @@ void elevator_set_none(struct request_queue *q)
 {
 	struct elv_change_ctx ctx = {
 		.name	= "none",
+		.quiesce_queue = true,
 	};
 	int err;
 
-- 
2.47.0