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

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Message-ID: <99297e45-e5d7-e582-ed66-4080baf5c884@kernel.dk>
Date:   Sun, 26 Feb 2023 13:18:36 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Tejun Heo <tj@...nel.org>, Breno Leitao <leitao@...ian.org>
Cc:     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

On 2/26/23 9:55 AM, Tejun Heo wrote:
> 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)?

Sorry missed this, I'll drop it for now.

-- 
Jens Axboe