linux-kernel - Re: [PATCH] blk-cgroup: validate alloc/free function pairs at the start of blkcg_policy

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Message-ID: <29be6f4e-fc0b-8134-fee6-7b3170f0d806@huaweicloud.com>
Date: Wed, 12 Feb 2025 10:26:52 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Michal Koutný <mkoutny@...e.com>,
 Chen Linxuan <chenlinxuan@...ontech.com>
Cc: Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>,
 Jens Axboe <axboe@...nel.dk>, Wen Tao <wentao@...ontech.com>,
 cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] blk-cgroup: validate alloc/free function pairs at the
 start of blkcg_policy_register()

Hi,

在 2025/02/11 21:57, Michal Koutný 写道:
> Hello Linxuan.
> 
> On Mon, Feb 10, 2025 at 11:18:27AM +0800, Chen Linxuan <chenlinxuan@...ontech.com> wrote:
>> Move the validation check for cpd/pd_alloc_fn and cpd/pd_free_fn function
>> pairs to the start of blkcg_policy_register(). This ensures we immediately
>> return -EINVAL if the function pairs are not correctly provided, rather
>> than returning -ENOSPC after locking and unlocking mutexes unnecessarily.
>>
>> Co-authored-by: Wen Tao <wentao@...ontech.com>
>> Signed-off-by: Wen Tao <wentao@...ontech.com>
>> Signed-off-by: Chen Linxuan <chenlinxuan@...ontech.com>
> 
> If you consider those locks contention a problem (policy registrations
> are "only" boot time, possibly module load time), then it's good to refer
> 
> Fixes: e84010732225c ("blkcg: add sanity check for blkcg policy operations")

This is super cold path, so I don't think it's a problem.
> 
>> ---
>>   block/blk-cgroup.c | 16 ++++++++--------
>>   1 file changed, 8 insertions(+), 8 deletions(-)
> 
> But it's correct,
> Reviewed-by: Michal Koutný <mkoutny@...e.com>
> 

Since we're here, can you also change the return value to -ENOMEM from
error path err_free_cpds?

Thanks,
Kuai