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block: restore default wbt enablement

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commit 8f5845e0743bf3512b71b3cb8afe06c192d6acc4 upstream.

The commit 245618f8e4 ("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 78c271344b ("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: 245618f8e4 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Julian Sun 2025-08-12 23:42:57 +08:00 committed by Greg Kroah-Hartman
parent 8b7b5f1477
commit a51d24abb2
1 changed files with 1 additions and 1 deletions
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2
block/blk-sysfs.c
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@ -876,9 +876,9 @@ 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);