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

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Message-ID: <aUMvIDRJegSVSicB@cmpxchg.org>
Date: Wed, 17 Dec 2025 17:30:56 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Qi Zheng <qi.zheng@...ux.dev>
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 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.