From: Laibin Qiu qiulaibin@huawei.com
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@rehdat.com Reviewed-by: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/linux-block/20211214133103.551813-1-qiulaibin@huawei... Signed-off-by: Laibin Qiu qiulaibin@huawei.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -6404,6 +6404,8 @@ 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 @@ -518,8 +518,6 @@ 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); } }