linux-kernel - Re: [PATCH] blk-iocost: initialize rqos before accessing it

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Date:   Sun, 26 Feb 2023 06:55:49 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Breno Leitao <leitao@...ian.org>
Cc:     axboe@...nel.dk, josef@...icpanda.com, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, aherrmann@...e.de,
        linux-kernel@...r.kernel.org, hch@....de, leit@...com
Subject: Re: [PATCH] blk-iocost: initialize rqos before accessing it

Hello, Breno.

On Fri, Feb 24, 2023 at 08:07:14AM -0800, Breno Leitao wrote:
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index ff534e9d92dc..6cced8a76e9c 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -2878,11 +2878,6 @@ static int blk_iocost_init(struct gendisk *disk)
>  	atomic64_set(&ioc->cur_period, 0);
>  	atomic_set(&ioc->hweight_gen, 0);
>  
> -	spin_lock_irq(&ioc->lock);
> -	ioc->autop_idx = AUTOP_INVALID;
> -	ioc_refresh_params(ioc, true);
> -	spin_unlock_irq(&ioc->lock);
> -
>  	/*
>  	 * rqos must be added before activation to allow ioc_pd_init() to
>  	 * lookup the ioc from q. This means that the rqos methods may get
> @@ -2893,6 +2888,11 @@ static int blk_iocost_init(struct gendisk *disk)
>  	if (ret)
>  		goto err_free_ioc;
>  
> +	spin_lock_irq(&ioc->lock);
> +	ioc->autop_idx = AUTOP_INVALID;
> +	ioc_refresh_params(ioc, true);
> +	spin_unlock_irq(&ioc->lock);
> +

I'm a bit worried about registering the rqos before ioc_refresh_params() as
that initializes all the internal parameters and letting IOs flow through
without initializing them can lead to subtle issues. Can you please instead
explicitly pass @q into ioc_refresh_params() (and explain why we need it
passed explicitly in the function comment)?

Thanks.

-- 
tejun