linux-kernel - Re: [PATCH -next 1/4] blk-iocost: track whether iocg is still online

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Date:   Mon, 26 Dec 2022 09:10:41 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Christoph Hellwig <hch@...radead.org>,
        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, yi.zhang@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next 1/4] blk-iocost: track whether iocg is still online

Hi, Christoph

在 2022/12/21 18:33, Christoph Hellwig 写道:
> 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
> .
>