block: restore default wbt enablement

The commit 245618f8e45f ("block: protect wbt_lat_usec using
q->elevator_lock") protected wbt_enable_default() with
q->elevator_lock; however, it also placed wbt_enable_default()
before blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);, resulting
in wbt failing to be enabled.

Moreover, the protection of wbt_enable_default() by q->elevator_lock
was removed in commit 78c271344b6f ("block: move wbt_enable_default()
out of queue freezing from sched ->exit()"), so we can directly fix
this issue by placing wbt_enable_default() after
blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);.

Additionally, this issue also causes the inability to read the
wbt_lat_usec file, and the scenario is as follows:

root@q:/sys/block/sda/queue# cat wbt_lat_usec
cat: wbt_lat_usec: Invalid argument

root@q:/data00/sjc/linux# ls /sys/kernel/debug/block/sda/rqos
cannot access '/sys/kernel/debug/block/sda/rqos': No such file or directory

root@q:/data00/sjc/linux# find /sys -name wbt
/sys/kernel/debug/tracing/events/wbt

After testing with this patch, wbt can be enabled normally.

Signed-off-by: Julian Sun <sunjunchao@bytedance.com>
Cc: stable@vger.kernel.org
Fixes: 245618f8e45f ("block: protect wbt_lat_usec using q->elevator_lock")
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250812154257.57540-1-sunjunchao@bytedance.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index c5cf79a2084222d688f28a01133d0daeabc5c873..4a7f1a349998bae6cb84bd3eeb7ab4547d91a81a 100644 (file)
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -902,9 +902,9 @@ int blk_register_queue(struct gendisk *disk)
 
        if (queue_is_mq(q))
                elevator_set_default(q);
-       wbt_enable_default(disk);
 
        blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);
+       wbt_enable_default(disk);
 
        /* Now everything is ready and send out KOBJ_ADD uevent */
        kobject_uevent(&disk->queue_kobj, KOBJ_ADD);