linux-kernel - Re: [PATCH] blk-cgroup: fix missing pd_online

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Date:   Wed, 4 Jan 2023 16:12:41 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
        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] blk-cgroup: fix missing pd_online_fn() while activating
 policy

Hello.

On Tue, Jan 03, 2023 at 07:28:33PM +0800, Yu Kuai <yukuai1@...weicloud.com> wrote:
> If the policy defines pd_online_fn(), it should be called after
> pd_init_fn(), like blkg_create().

Is this based only on code review or has it some negative effects?

I assume this would affect hot-plugged (read after cgroup creation) devices.

I took a cursory look at:

	blkcg_init_disk
	  blkg_create
	    pol->pd_init_fn(blkg->pd[i]);
	    pol->pd_online_fn(blkg->pd[i]);
	  blk_throtl_init
	    blkcg_activate_policy
	      pol->pd_init_fn(blkg->pd[i]);
	      ?? pol->pd_online_fn(blkg->pd[i]);

I.e. the pd_online_fn is already called and pd_init_fn is called 2nd
time? 

Thanks,
Michal

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