From e92bc4cd34de2ce454bdea8cd198b8067ee4e123 Mon Sep 17 00:00:00 2001 From: Laibin Qiu Date: Sat, 22 Jan 2022 19:10:45 +0800 Subject: block/wbt: fix negative inflight counter when remove scsi device 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 Reviewed-by: Christoph Hellwig Link: https://lore.kernel.org/linux-block/20211214133103.551813-1-qiulaibin@huawei.com/ Signed-off-by: Laibin Qiu Signed-off-by: Jens Axboe --- block/bfq-iosched.c | 2 ++ block/elevator.c | 2 -- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 0c612a911696..36a66e97e3c2 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -7018,6 +7018,8 @@ static void bfq_exit_queue(struct elevator_queue *e) spin_unlock_irq(&bfqd->lock); #endif + wbt_enable_default(bfqd->queue); + kfree(bfqd); } diff --git a/block/elevator.c b/block/elevator.c index ec98aed39c4f..482df2a350fc 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -525,8 +525,6 @@ void elv_unregister_queue(struct request_queue *q) kobject_del(&e->kobj); e->registered = 0; - /* Re-enable throttling in case elevator disabled it */ - wbt_enable_default(q); } } -- cgit v1.2.3-59-g8ed1b