From: Laibin Qiu <qiulaibin@xxxxxxxxxx> commit e92bc4cd34de2ce454bdea8cd198b8067ee4e123 upstream. Now that we disable wbt by set WBT_STATE_OFF_DEFAULT in wbt_disable_default() when switch elevator to bfq. And when we remove scsi device, wbt will be enabled by wbt_enable_default. If it become false positive between wbt_wait() and wbt_track() when submit write request. The following is the scenario that triggered the problem. T1 T2 T3 elevator_switch_mq bfq_init_queue wbt_disable_default <= Set rwb->enable_state (OFF) Submit_bio blk_mq_make_request rq_qos_throttle <= rwb->enable_state (OFF) scsi_remove_device sd_remove del_gendisk blk_unregister_queue elv_unregister_queue wbt_enable_default <= Set rwb->enable_state (ON) q_qos_track <= rwb->enable_state (ON) ^^^^^^ this request will mark WBT_TRACKED without inflight add and will lead to drop rqw->inflight to -1 in wbt_done() which will trigger IO hung. Fix this by move wbt_enable_default() from elv_unregister to bfq_exit_queue(). Only re-enable wbt when bfq exit. Fixes: 76a8040817b4b ("blk-wbt: make sure throttle is enabled properly") Remove oneline stale comment, and kill one oneshot local variable. Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Link: https://lore.kernel.org/linux-block/20211214133103.551813-1-qiulaibin@xxxxxxxxxx/ Signed-off-by: Laibin Qiu <qiulaibin@xxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/bfq-iosched.c | 2 ++ block/elevator.c | 2 -- 2 files changed, 2 insertions(+), 2 deletions(-) --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6878,6 +6878,8 @@ static void bfq_exit_queue(struct elevat spin_unlock_irq(&bfqd->lock); #endif + wbt_enable_default(bfqd->queue); + kfree(bfqd); } --- a/block/elevator.c +++ b/block/elevator.c @@ -523,8 +523,6 @@ void elv_unregister_queue(struct request kobject_del(&e->kobj); e->registered = 0; - /* Re-enable throttling in case elevator disabled it */ - wbt_enable_default(q); } } Patches currently in stable-queue which might be from qiulaibin@xxxxxxxxxx are queue-5.16/block-wbt-fix-negative-inflight-counter-when-remove-scsi-device.patch