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

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Message-ID: <i6owvzwb4pjg27tex5utdzcoyeeawqejegvc2byz6tnfn2flmh@2ggun5qyokvs>
Date: Tue, 11 Feb 2025 14:57:09 +0100
From: Michal Koutný <mkoutny@...e.com>
To: 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
Subject: Re: [PATCH] blk-cgroup: validate alloc/free function pairs at the
 start of blkcg_policy_register()

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")

> ---
>  block/blk-cgroup.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)

But it's correct,
Reviewed-by: Michal Koutný <mkoutny@...e.com>

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