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

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Message-ID: <4c8f1e4e-1b15-4afa-b1e2-084e0c4caeec@acm.org>
Date: Thu, 11 Jul 2024 11:03:52 -0700
From: Bart Van Assche <bvanassche@....org>
To: Yu Kuai <yukuai1@...weicloud.com>, tj@...nel.org, josef@...icpanda.com,
 jack@...e.cz, axboe@...nel.dk
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH 2/2] blk-ioprio: remove per-disk structure

On 7/11/24 2:00 AM, Yu Kuai wrote:
> ioprio works on the blk-cgroup level, all disks in the same cgroup
> are the same, and the struct ioprio_blkg doesn't have anything in it.
> Hence register the policy is enough, because cpd_alloc/free_fn will
> be handled for each blk-cgroup, and there is no need to activate the
> policy for disk.

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?

Thanks,

Bart.