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From:   Jens Axboe <axboe@kernel.dk>
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
        yukuai3@huawei.com, yi.zhang@huawei.com
In-Reply-To: <20220913105749.3086243-1-yukuai1@huaweicloud.com>
References: <20220913105749.3086243-1-yukuai1@huaweicloud.com>
Subject: Re: [PATCH -next] blk-wbt: call rq_qos_add() after wb_normal is initialized
Message-Id: <166377102908.42944.10712630540231766457.b4-ty@kernel.dk>
Date:   Wed, 21 Sep 2022 08:37:09 -0600
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Precedence: bulk

On Tue, 13 Sep 2022 18:57:49 +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Our test found a problem that wbt inflight counter is negative, which
> will cause io hang(noted that this problem doesn't exist in mainline):
> 
> t1: device create	t2: issue io
> add_disk
>  blk_register_queue
>   wbt_enable_default
>    wbt_init
>     rq_qos_add
>     // wb_normal is still 0
> 			/*
> 			 * in mainline, disk can't be opened before
> 			 * bdev_add(), however, in old kernels, disk
> 			 * can be opened before blk_register_queue().
> 			 */
> 			blkdev_issue_flush
>                         // disk size is 0, however, it's not checked
>                          submit_bio_wait
>                           submit_bio
>                            blk_mq_submit_bio
>                             rq_qos_throttle
>                              wbt_wait
> 			      bio_to_wbt_flags
>                                rwb_enabled
> 			       // wb_normal is 0, inflight is not increased
> 
> [...]

Applied, thanks!

[1/1] blk-wbt: call rq_qos_add() after wb_normal is initialized
      commit: 8c5035dfbb9475b67c82b3fdb7351236525bf52b

Best regards,
-- 
Jens Axboe