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c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1766715131; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EC9PlpSlHlSGM8vUpGB7O9CFtRBGbGwH+yCe/FQZv30=; b=zRkkZ8w5QuPJL0Y5nnG7eri4zaCsn9azlTu1YqsXPmSU7a9gO02gkIU4mvvz0kudAMDXjD 2dzKEtxn0QEGrbNW56vaxtt/VfyhW6RBfBLMkUcu13Xa9t3eUV/SLUOtpAGLevibRIrAHX CypjBkxYY6Z55BFpTBgRPrfya8dje/4= Received: from mail.maildlp.com (unknown [172.19.163.177]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4dcpyN4nkhzKHMLL for ; Fri, 26 Dec 2025 10:11:40 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id DB47B40590 for ; Fri, 26 Dec 2025 10:12:02 +0800 (CST) Received: from [10.67.111.176] (unknown [10.67.111.176]) by APP4 (Coremail) with SMTP id gCh0CgA35vbx7k1p_fwCBg--.54121S2; Fri, 26 Dec 2025 10:12:02 +0800 (CST) Message-ID: <8354b8b7-2d94-431b-b60a-6a744ab7ca06@huaweicloud.com> Date: Fri, 26 Dec 2025 10:12:01 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 11/28] mm: memcontrol: prevent memory cgroup release in count_memcg_folio_events() To: Qi Zheng , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng References: <5f8032bc300b7c12e61446ba4f3d28fba5a7d9d5.1765956025.git.zhengqi.arch@bytedance.com> Content-Language: en-US From: Chen Ridong In-Reply-To: <5f8032bc300b7c12e61446ba4f3d28fba5a7d9d5.1765956025.git.zhengqi.arch@bytedance.com> Content-Type: text/plain; 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To ensure safety, it will only be appropriate to > hold the rcu read lock or acquire a reference to the memory cgroup > returned by folio_memcg(), thereby preventing it from being released. > > In the current patch, the rcu read lock is employed to safeguard > against the release of the memory cgroup in count_memcg_folio_events(). > > This serves as a preparatory measure for the reparenting of the > LRU pages. > > Signed-off-by: Muchun Song > Signed-off-by: Qi Zheng > Reviewed-by: Harry Yoo > --- > include/linux/memcontrol.h | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index bc526e0d37e0b..69c4bcfb3c3cd 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -974,10 +974,15 @@ void count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx, > static inline void count_memcg_folio_events(struct folio *folio, > enum vm_event_item idx, unsigned long nr) > { > - struct mem_cgroup *memcg = folio_memcg(folio); > + struct mem_cgroup *memcg; > > - if (memcg) > - count_memcg_events(memcg, idx, nr); > + if (!folio_memcg_charged(folio)) > + return; > + > + rcu_read_lock(); > + memcg = folio_memcg(folio); > + count_memcg_events(memcg, idx, nr); > + rcu_read_unlock(); > } > > static inline void count_memcg_events_mm(struct mm_struct *mm, Reviewed-by: Chen Ridong -- Best regards, Ridong