linux-kernel - Re: [PATCH v2 23/28] mm: memcontrol: prepare for reparenting LRU pages for lruvec lock

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Message-ID: <ffc68aa4-cb9d-465f-8c6f-9cd7315eb560@linux.dev>
Date: Tue, 23 Dec 2025 14:14:09 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com,
 roman.gushchin@...ux.dev, muchun.song@...ux.dev, david@...nel.org,
 lorenzo.stoakes@...cle.com, ziy@...dia.com, harry.yoo@...cle.com,
 imran.f.khan@...cle.com, kamalesh.babulal@...cle.com,
 axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
 chenridong@...weicloud.com, mkoutny@...e.com, akpm@...ux-foundation.org,
 hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com,
 lance.yang@...ux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, Muchun Song <songmuchun@...edance.com>,
 Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 23/28] mm: memcontrol: prepare for reparenting LRU
 pages for lruvec lock



On 12/20/25 10:03 AM, Shakeel Butt wrote:
> On Wed, Dec 17, 2025 at 03:27:47PM +0800, Qi Zheng wrote:
>> @@ -1232,14 +1221,20 @@ struct lruvec *folio_lruvec_lock(struct folio *folio)
>>    * - folio frozen (refcount of 0)
>>    *
>>    * Return: The lruvec this folio is on with its lock held and interrupts
>> - * disabled.
>> + * disabled and rcu read lock held.
>>    */
>>   struct lruvec *folio_lruvec_lock_irq(struct folio *folio)
>>   {
>> -	struct lruvec *lruvec = folio_lruvec(folio);
>> +	struct lruvec *lruvec;
>>   
>> +	rcu_read_lock();
>> +retry:
>> +	lruvec = folio_lruvec(folio);
>>   	spin_lock_irq(&lruvec->lru_lock);
>> -	lruvec_memcg_debug(lruvec, folio);
>> +	if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) {
>> +		spin_unlock_irq(&lruvec->lru_lock);
>> +		goto retry;
>> +	}
> 
> So after this patch, all folio_lruvec_lock_irq() calls should be paired
> with lruvec_unlock_irq() but lru_note_cost_refault() is calling
> folio_lruvec_lock_irq() without the paired lruvec_unlock_irq(). It is
> using lru_note_cost_unlock_irq() for unlocking lru lock and thus rcu
> read unlock is missed.

Indeed. Will fix in the next version.

> 
> Beside fixing this, I would suggest to add __acquire()/__release() tags
> for both lru lock and rcu for all these functions.

OK, will do.


Thanks,
Qi

>