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Date:   Tue, 19 Jul 2022 09:53:55 -0600
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Subject: Re: [PATCH v2] block: don't allow the same type rq_qos add more than
 once
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To:     Jinke Han <hanjinke.666@bytedance.com>, tj@kernel.org
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org
References: <20220719070258.25721-1-hanjinke.666@bytedance.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <20220719070258.25721-1-hanjinke.666@bytedance.com>
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On 7/19/22 1:02 AM, Jinke Han wrote:
> From: Jinke Han <hanjinke.666@bytedance.com>
> 
> In our test of iocost, we encounttered some list add/del corrutions of

encountered and corruptions

> inner_walk list in ioc_timer_fn.
> 
> The reason can be descripted as follow:

described

> cpu 0						cpu 1
> ioc_qos_write					ioc_qos_write
> 
> ioc = q_to_ioc(bdev_get_queue(bdev));
> if (!ioc) {
>         ioc = kzalloc();			ioc = q_to_ioc(bdev_get_queue(bdev));
> 						if (!ioc) {
> 							ioc = kzalloc();
> 							...
> 							rq_qos_add(q, rqos);
> 						}
>         ...
>         rq_qos_add(q, rqos);
>         ...
> }
> 
> When the io.cost.qos file is written by two cpu concurrently, rq_qos may

two cpus

> be added to one disk twice. In that case, there will be two iocs enabled
> and running on one disk. They own different iocgs on their active list.
> In the ioc_timer_fn function, because of the iocgs from two ioc have the
> same root iocg, the root iocg's walk_list may be overwritten by each
> other and this lead to list add/del corrutions in building or destorying

leads to, corruptions, destroying.

Outside of the spelling and grammer which I typically just fix up while
applying, this one doesn't apply to for-5.20/block. Please check and
resend it.

-- 
Jens Axboe