linux-kernel - [PATCH 4/5] blk-iolatency: fix incorrect lock order for rq_qos

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Message-Id: <20251116024134.115685-5-yukuai@fnnas.com>
Date: Sun, 16 Nov 2025 10:41:33 +0800
From: "Yu Kuai" <yukuai@...as.com>
To: <axboe@...nel.dk>, <linux-block@...r.kernel.org>, 
	<linux-kernel@...r.kernel.org>, <tj@...nel.org>, <nilay@...ux.ibm.com>, 
	<ming.lei@...hat.com>
Cc: <yukuai@...as.com>
Subject: [PATCH 4/5] blk-iolatency: fix incorrect lock order for rq_qos_mutex and freeze queue

Currently blk-iolatency will hold rq_qos_mutex first and then call
rq_qos_add() to freeze queue.

Fix this problem by converting to use blkg_conf_open_bdev_frozen()
from iolatency_set_limit(), and convert to use rq_qos_add_freezed().

Signed-off-by: Yu Kuai <yukuai@...as.com>
---
 block/blk-iolatency.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 45bd18f68541..1565352b176d 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -764,8 +764,8 @@ static int blk_iolatency_init(struct gendisk *disk)
 	if (!blkiolat)
 		return -ENOMEM;
 
-	ret = rq_qos_add(&blkiolat->rqos, disk, RQ_QOS_LATENCY,
-			 &blkcg_iolatency_ops);
+	ret = rq_qos_add_freezed(&blkiolat->rqos, disk, RQ_QOS_LATENCY,
+				 &blkcg_iolatency_ops);
 	if (ret)
 		goto err_free;
 	ret = blkcg_activate_policy(disk, &blkcg_policy_iolatency);
@@ -831,16 +831,19 @@ static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
 	struct blkcg_gq *blkg;
 	struct blkg_conf_ctx ctx;
 	struct iolatency_grp *iolat;
+	unsigned long memflags;
 	char *p, *tok;
 	u64 lat_val = 0;
 	u64 oldval;
-	int ret;
+	int ret = 0;
 
 	blkg_conf_init(&ctx, buf);
 
-	ret = blkg_conf_open_bdev(&ctx);
-	if (ret)
+	memflags = blkg_conf_open_bdev_frozen(&ctx);
+	if (IS_ERR_VALUE(memflags)) {
+		ret = memflags;
 		goto out;
+	}
 
 	/*
 	 * blk_iolatency_init() may fail after rq_qos_add() succeeds which can
@@ -890,7 +893,7 @@ static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
 		iolatency_clear_scaling(blkg);
 	ret = 0;
 out:
-	blkg_conf_exit(&ctx);
+	blkg_conf_exit_frozen(&ctx, memflags);
 	return ret ?: nbytes;
 }
 
-- 
2.51.0