linux-kernel - Re: [PATCH 2/2] blk-ioprio: remove per-disk structure

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Message-ID: <7803ebeb-32a1-57a9-2a65-b44de8f42eed@huaweicloud.com>
Date: Fri, 12 Jul 2024 14:51:50 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Christoph Hellwig <hch@...radead.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: Bart Van Assche <bvanassche@....org>, tj@...nel.org,
 josef@...icpanda.com, jack@...e.cz, axboe@...nel.dk,
 cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 2/2] blk-ioprio: remove per-disk structure

Hi,

在 2024/07/12 13:22, Christoph Hellwig 写道:
> On Fri, Jul 12, 2024 at 09:10:30AM +0800, Yu Kuai wrote:
>>> As one can see in the output of git grep -nHEB1 '>pd_(alloc|free)_fn\(',
>>> none of the pd_alloc_fn / pd_free_fn callers checks whether or not these
>>> pointers are NULL. Hence my question why this patch does not trigger any
>>> NULL pointer dereferences?
>>
>> Because the blkcg_deactivate_policy() is removed as well, there are no
>> callers now... blkcg_policy_register() is still called to make sure
>> cpd_(alloc|free)_fn will still be called.
> 
> Can you throw in a patch documenting this?  Any maybe add a check
> that pd_alloc_fn / pd_free_fn exist in blkcg_activate_policy and
> WARN and return an error otherwise?

Of course, I realized now that just mention don't activate the policy
from commit message is too little explanation.

Thanks,
Kuai

> 
> .
>