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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1765956644; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cb8NWIyZ/ts5sKA8lazTxoYJ+MrmJmaOEPm0Hg1IF8Q=; b=ZrvJVvvWuNeMXQL9pMRHM4uWZyvvIGS4eeGanGz2oB/X+b3VfcEuyVIps/0tthZkAdqdER WYYXtlOzeXulJisgMUeJS2MAmu/yMhGhzaCnO4JeGiEvFWXmp/3gOQMVYWVe8xAjW17tZ+ omsRM5kP270T8TDwabvlJGBS3joq4mA= From: Qi Zheng To: 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, chenridong@huaweicloud.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 Subject: [PATCH v2 10/28] writeback: prevent memory cgroup release in writeback module Date: Wed, 17 Dec 2025 15:27:34 +0800 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: hxmgs93m6bsc1axxqc9grw3wt6jg3sug X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 0CC5DA0007 X-Rspam-User: X-HE-Tag: 1765956650-693037 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Muchun Song In the near future, a folio will no longer pin its corresponding memory cgroup. 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 function get_mem_cgroup_css_from_folio() and the rcu read lock are employed to safeguard against the release of the memory cgroup. 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 --- fs/fs-writeback.c | 22 +++++++++++----------- include/linux/memcontrol.h | 9 +++++++-- include/trace/events/writeback.h | 3 +++ mm/memcontrol.c | 14 ++++++++------ 4 files changed, 29 insertions(+), 19 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 5dd6e89a6d29e..2e57b7e2b4453 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -279,15 +279,13 @@ void __inode_attach_wb(struct inode *inode, struct folio *folio) if (inode_cgwb_enabled(inode)) { struct cgroup_subsys_state *memcg_css; - if (folio) { - memcg_css = mem_cgroup_css_from_folio(folio); - wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); - } else { - /* must pin memcg_css, see wb_get_create() */ + /* must pin memcg_css, see wb_get_create() */ + if (folio) + memcg_css = get_mem_cgroup_css_from_folio(folio); + else memcg_css = task_get_css(current, memory_cgrp_id); - wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); - css_put(memcg_css); - } + wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); + css_put(memcg_css); } if (!wb) @@ -979,16 +977,16 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct folio *folio if (!wbc->wb || wbc->no_cgroup_owner) return; - css = mem_cgroup_css_from_folio(folio); + css = get_mem_cgroup_css_from_folio(folio); /* dead cgroups shouldn't contribute to inode ownership arbitration */ if (!css_is_online(css)) - return; + goto out; id = css->id; if (id == wbc->wb_id) { wbc->wb_bytes += bytes; - return; + goto out; } if (id == wbc->wb_lcand_id) @@ -1001,6 +999,8 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct folio *folio wbc->wb_tcand_bytes += bytes; else wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes); +out: + css_put(css); } EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner); diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 776d9be1f446a..bc526e0d37e0b 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -895,7 +895,7 @@ static inline bool mm_match_cgroup(struct mm_struct *mm, return match; } -struct cgroup_subsys_state *mem_cgroup_css_from_folio(struct folio *folio); +struct cgroup_subsys_state *get_mem_cgroup_css_from_folio(struct folio *folio); ino_t page_cgroup_ino(struct page *page); static inline bool mem_cgroup_online(struct mem_cgroup *memcg) @@ -1549,9 +1549,14 @@ static inline void mem_cgroup_track_foreign_dirty(struct folio *folio, if (mem_cgroup_disabled()) return; + if (!folio_memcg_charged(folio)) + return; + + rcu_read_lock(); memcg = folio_memcg(folio); - if (unlikely(memcg && &memcg->css != wb->memcg_css)) + if (unlikely(&memcg->css != wb->memcg_css)) mem_cgroup_track_foreign_dirty_slowpath(folio, wb); + rcu_read_unlock(); } void mem_cgroup_flush_foreign(struct bdi_writeback *wb); diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h index 311a341e6fe42..f5bfe8c1a160a 100644 --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -295,7 +295,10 @@ TRACE_EVENT(track_foreign_dirty, __entry->ino = inode ? inode->i_ino : 0; __entry->memcg_id = wb->memcg_css->id; __entry->cgroup_ino = __trace_wb_assign_cgroup(wb); + + rcu_read_lock(); __entry->page_cgroup_ino = cgroup_ino(folio_memcg(folio)->css.cgroup); + rcu_read_unlock(); ), TP_printk("bdi %s[%llu]: ino=%lu memcg_id=%u cgroup_ino=%lu page_cgroup_ino=%lu", diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 431b3154c70c5..131f940c03fa0 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -241,7 +241,7 @@ DEFINE_STATIC_KEY_FALSE(memcg_bpf_enabled_key); EXPORT_SYMBOL(memcg_bpf_enabled_key); /** - * mem_cgroup_css_from_folio - css of the memcg associated with a folio + * get_mem_cgroup_css_from_folio - acquire a css of the memcg associated with a folio * @folio: folio of interest * * If memcg is bound to the default hierarchy, css of the memcg associated @@ -251,14 +251,16 @@ EXPORT_SYMBOL(memcg_bpf_enabled_key); * If memcg is bound to a traditional hierarchy, the css of root_mem_cgroup * is returned. */ -struct cgroup_subsys_state *mem_cgroup_css_from_folio(struct folio *folio) +struct cgroup_subsys_state *get_mem_cgroup_css_from_folio(struct folio *folio) { - struct mem_cgroup *memcg = folio_memcg(folio); + struct mem_cgroup *memcg; - if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys)) - memcg = root_mem_cgroup; + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) + return &root_mem_cgroup->css; - return &memcg->css; + memcg = get_mem_cgroup_from_folio(folio); + + return memcg ? &memcg->css : &root_mem_cgroup->css; } /** -- 2.20.1