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Subject: Re: [PATCH -next 1/4] blk-iocost: track whether iocg is still online
To:     Christoph Hellwig <hch@infradead.org>,
        Yu Kuai <yukuai1@huaweicloud.com>
Cc:     tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20221217030527.1250083-1-yukuai1@huaweicloud.com>
 <20221217030527.1250083-2-yukuai1@huaweicloud.com>
 <Y6LhD8CEkcgLUJoQ@infradead.org>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <edb84ee2-3dd5-8bb4-4417-ed42744d793f@huaweicloud.com>
Date:   Mon, 26 Dec 2022 09:10:41 +0800
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Hi, Christoph

?? 2022/12/21 18:33, Christoph Hellwig д??:
> On Sat, Dec 17, 2022 at 11:05:24AM +0800, Yu Kuai wrote:
>> @@ -459,6 +459,8 @@ struct ioc_gq {
>>   	struct blkg_policy_data		pd;
>>   	struct ioc			*ioc;
>>   
>> +	bool online;
> 
> Nit: maybe tab align this field like the fields above it.
> 
>> +static void ioc_pd_offline(struct blkg_policy_data *pd)
>> +{
>> +	struct ioc_gq *iocg = pd_to_iocg(pd);
>> +	struct ioc *ioc = iocg->ioc;
>> +	unsigned long flags;
>> +
>> +	if (ioc) {
> 
> How could ioc be NULL here?
> 

As I explained in another thread.. pd_offline_fn() can be called without
pd_init_fn(), which is a bug from upper layer...

blkcg_activate_policy
  spin_lock_irq(&q->queue_lock);
  list_for_each_entry_reverse(blkg, &q->blkg_list
   pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN,...) -> failed

   spin_unlock_irq(&q->queue_lock);
   // release queue_lock here is problematic, this will cause
pd_offline_fn called without pd_init_fn.
   pd_alloc_fn(__GFP_NOWARN,...)

Thanks,
Kuai
> .
>