linux-kernel - Re: [PATCH v2 19/28] mm: workingset: prevent lruvec release in workingset

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Message-ID: <70b14272-10b8-4dbb-9f49-40ea9f9103bd@linux.dev>
Date: Thu, 18 Dec 2025 14:57:05 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Johannes Weiner <hannes@...xchg.org>
Cc: hughd@...gle.com, mhocko@...e.com, roman.gushchin@...ux.dev,
 shakeel.butt@...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 19/28] mm: workingset: prevent lruvec release in
 workingset_refault()



On 12/18/25 6:30 AM, Johannes Weiner wrote:
> On Wed, Dec 17, 2025 at 03:27:43PM +0800, Qi Zheng wrote:
>> From: Muchun Song <songmuchun@...edance.com>
>>
>> In the near future, a folio will no longer pin its corresponding
>> memory cgroup. So an lruvec returned by folio_lruvec() could be
>> released without the rcu read lock or a reference to its memory
>> cgroup.
>>
>> In the current patch, the rcu read lock is employed to safeguard
>> against the release of the lruvec in workingset_refault().
>>
>> This serves as a preparatory measure for the reparenting of the
>> LRU pages.
>>
>> Signed-off-by: Muchun Song <songmuchun@...edance.com>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
>> ---
>>   mm/workingset.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/workingset.c b/mm/workingset.c
>> index 445fc634196d8..427ca1a5625e8 100644
>> --- a/mm/workingset.c
>> +++ b/mm/workingset.c
>> @@ -560,11 +560,12 @@ void workingset_refault(struct folio *folio, void *shadow)
>>   	 * locked to guarantee folio_memcg() stability throughout.
>>   	 */
>>   	nr = folio_nr_pages(folio);
>> +	rcu_read_lock();
>>   	lruvec = folio_lruvec(folio);
>>   	mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
>>   
>>   	if (!workingset_test_recent(shadow, file, &workingset, true))
> 
> This might sleep. You have to get a reference here and unlock RCU.

Indeed, this may sleep in css_rstat_flush().

Will do the following:

get_mem_cgroup_from_folio(folio);
lruvec = mem_cgroup_lruvec(memcg, folio_pgdat(folio));

/* xxx */

mem_cgroup_put(memcg);