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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772005865; 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=7g4zlvI4KL5BM3hQhoVvcLwONpSLS6QDIXKeCKwliro=; b=QyTpyBemrEemSPovJqik1g1xMtszEVeXZTEVpK9vIyrraK29LWm8EfiWvYJ0/9qB6QH13H ZPRe4QfxI1ucZU9acWwkLDTq2RsSNpk1CJnAp1qL/0Cz3XfjtpZ/1PbDrE2NdfVG1f1E4S P1qIeUOIX2wzqlwneyqBSF3fYHT4dOc= 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, yosry.ahmed@linux.dev, 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, bhe@redhat.com, usamaarif642@gmail.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng Subject: [PATCH v5 10/32] writeback: prevent memory cgroup release in writeback module Date: Wed, 25 Feb 2026 15:48:43 +0800 Message-ID: <645f99bc344575417f67def3744f975596df2793.1772005110.git.zhengqi.arch@bytedance.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: fnhuq9wpf8aitzyazby4cmjutwsbx95w X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E4B06C0005 X-HE-Tag: 1772005866-224547 X-HE-Meta: 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 id0s83Ps Kkn9cpOByDnim97/5kMa4n10igdqnplxzkXilQBKQMkbXC6b0cq942CbFdO10FhzUDGwu74IDuThfjZukU0rgHxtnaVaeGk3FeTzckHpMsjC7TbQdGO6nHva+2yT1UB44NPQSqFfp/vBpKCibxbsuwvM2itXRxkPq/R5ll1DUCFX9/BN0RKJ2URwrL1A6TgF1BUQD2cOZNl1tfzNfnE7kmraTkgcSeboA2jsHoksDbMSwR+03ZneIkZlhagR633a10gHcrRuVxFhJaJI74WGypKZPMMv0GmjSXcLjUMofY+5qs1I= 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 Acked-by: Johannes Weiner Acked-by: Shakeel Butt --- 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 7c75ed7e89799..c3442a38450ca 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -280,15 +280,13 @@ 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 f4b6158b77d8e..20d38262b984b 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) @@ -1564,9 +1564,14 @@ 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 4d3d8c8f3a1bc..b849b8cc96b1e 100644 --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -294,7 +294,10 @@ 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 4820919c0d219..a4bb8b8b2c457 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -244,7 +244,7 @@ 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 @@ -254,14 +254,16 @@ 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