Like wbt, rq_qos_add() can be called from two path and the lock order
are inversely:

- From ioc_qos_write(), queue is already freezed before rq_qos_add();
- From ioc_cost_model_write(), rq_qos_add() is called directly;

Fix this problem by converting to use blkg_conf_open_bdev_frozen()
from ioc_cost_model_write(), then since all rq_qos_add() callers
already freeze queue, convert to use rq_qos_add_freezed.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
---
 block/blk-iocost.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 5bfd70311359..233c9749bfc9 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2927,7 +2927,7 @@ static int blk_iocost_init(struct gendisk *disk)
 	 * called before policy activation completion, can't assume that the
 	 * target bio has an iocg associated and need to test for NULL iocg.
 	 */
-	ret = rq_qos_add(&ioc->rqos, disk, RQ_QOS_COST, &ioc_rqos_ops);
+	ret = rq_qos_add_freezed(&ioc->rqos, disk, RQ_QOS_COST, &ioc_rqos_ops);
 	if (ret)
 		goto err_free_ioc;
 
@@ -3410,7 +3410,7 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 {
 	struct blkg_conf_ctx ctx;
 	struct request_queue *q;
-	unsigned int memflags;
+	unsigned long memflags;
 	struct ioc *ioc;
 	u64 u[NR_I_LCOEFS];
 	bool user;
@@ -3419,9 +3419,11 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 
 	blkg_conf_init(&ctx, input);
 
-	ret = blkg_conf_open_bdev(&ctx);
-	if (ret)
+	memflags = blkg_conf_open_bdev_frozen(&ctx);
+	if (IS_ERR_VALUE(memflags)) {
+		ret = memflags;
 		goto err;
+	}
 
 	body = ctx.body;
 	q = bdev_get_queue(ctx.bdev);
@@ -3438,7 +3440,6 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 		ioc = q_to_ioc(q);
 	}
 
-	memflags = blk_mq_freeze_queue(q);
 	blk_mq_quiesce_queue(q);
 
 	spin_lock_irq(&ioc->lock);
@@ -3490,20 +3491,18 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
 	spin_unlock_irq(&ioc->lock);
 
 	blk_mq_unquiesce_queue(q);
-	blk_mq_unfreeze_queue(q, memflags);
 
-	blkg_conf_exit(&ctx);
+	blkg_conf_exit_frozen(&ctx, memflags);
 	return nbytes;
 
 einval:
 	spin_unlock_irq(&ioc->lock);
 
 	blk_mq_unquiesce_queue(q);
-	blk_mq_unfreeze_queue(q, memflags);
 
 	ret = -EINVAL;
 err:
-	blkg_conf_exit(&ctx);
+	blkg_conf_exit_frozen(&ctx, memflags);
 	return ret;
 }
 
-- 
2.51.0

On 11/16/25 9:40 AM, Yu Kuai wrote:
> Like wbt, rq_qos_add() can be called from two path and the lock order
> are inversely:
> 
> - From ioc_qos_write(), queue is already freezed before rq_qos_add();
> - From ioc_cost_model_write(), rq_qos_add() is called directly;
> 
> Fix this problem by converting to use blkg_conf_open_bdev_frozen()
> from ioc_cost_model_write(), then since all rq_qos_add() callers
> already freeze queue, convert to use rq_qos_add_freezed.
> 
> Signed-off-by: Yu Kuai <yukuai@fnnas.com>

Looks good to me:
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>