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Subject: Re: [PATCH] blk-iocost: do not WARNING if iocg has already offlined
To: linan666@huaweicloud.com, tj@kernel.org, josef@toxicpanda.com,
 axboe@kernel.dk
Cc: hch@lst.de, cgroups@vger.kernel.org, linux-block@vger.kernel.org,
 linux-kernel@vger.kernel.org, yi.zhang@huawei.com, houtao1@huawei.com,
 yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20240418072340.2090877-1-linan666@huaweicloud.com>
From: Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <75a8212a-a6ff-416c-7bce-0f4036a4abc0@huaweicloud.com>
Date: Thu, 18 Apr 2024 16:52:24 +0800
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?? 2024/04/18 15:23, linan666@huaweicloud.com д??:
> From: Li Nan <linan122@huawei.com>
> 
> In iocg_pay_debt(), warn is triggered if 'active_list' is empty, which
> is intended to confirm iocg is avitve when it has debt. However, warn
> can be triggered during removing cgroup controller, as
> iocg_waitq_timer_fn() is awakened at that time.
> 
>    WARNING: CPU: 0 PID: 2344971 at block/blk-iocost.c:1402 iocg_pay_debt+0x14c/0x190

This line doesn't match the code from mainline, please mention that
which kernel release you're testing.

Other than that, ioc_pd_free() indeed clear 'active_list' before
canceling the timer, this patch looks good to me.

Reviewed-by: Yu Kuai <yukuai3@huawei.com>
>    Call trace:
>    iocg_pay_debt+0x14c/0x190
>    iocg_kick_waitq+0x438/0x4c0
>    iocg_waitq_timer_fn+0xd8/0x130
>    __run_hrtimer+0x144/0x45c
>    __hrtimer_run_queues+0x16c/0x244
>    hrtimer_interrupt+0x2cc/0x7b0
> 
> The warn in this situation is meaningless. Since this iocg is being
> removed, the state of the 'active_list' is irrelevant, and 'waitq_timer'
> is canceled after removing 'active_list' in ioc_pd_free(), which ensure
> iocg is freed after iocg_waitq_timer_fn() returns.
> 
> Therefore, add the check if iocg has already offlined to avoid warn
> when removing cgroup controller.
> 
> Signed-off-by: Li Nan <linan122@huawei.com>
> ---
>   block/blk-iocost.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index baa20c85799d..2e109c016a39 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -1440,7 +1440,7 @@ static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay,
>   	lockdep_assert_held(&iocg->waitq.lock);
>   
>   	/* make sure that nobody messed with @iocg */
> -	WARN_ON_ONCE(list_empty(&iocg->active_list));
> +	WARN_ON_ONCE(list_empty(&iocg->active_list) && iocg->pd.online);
>   	WARN_ON_ONCE(iocg->inuse > 1);
>   
>   	iocg->abs_vdebt -= min(abs_vpay, iocg->abs_vdebt);
>