From nobody Thu Dec 18 08:29:52 2025 Received: from mail-pf1-f179.google.com (mail-pf1-f179.google.com [209.85.210.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E0D3198831 for ; Thu, 25 Jul 2024 09:43:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.179 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721900625; cv=none; b=BVBbfb2w6jvVcvW+ncwN42nnCXiYsRE2TvSzai7f0NTnNvXtifZQo17f3k2gYf6fmmL/yJ+/Z5PBNUfSzB7t0QA6IGP/3jwGO6JRC3srpATJBvSsVN4a53rlMzWO5qv25HpXMXomqxIakTE9hCyuPTiip/gMC+CG1Wl4WzPeEGU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721900625; c=relaxed/simple; bh=/YjnkXOScXDrIAsihbMrWMI2ywu8cO7TH5Ge7ewZVCw=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=JQ8ySb6tqOd7yRjVuSTxeP5kAhf5YeOeUc7wBPbCoWasfBKmPIJxWyrWXbj53C1fRZta98M2WjcyMJOMBhbaEdS9XhXsI8iAeZxGbGgamfPEQ/wSpJfF1wUaE1IopmCg2bgeqYyrj+1bcSyt5x9O9+RW8z+MV4jC7yWxbI0zoYY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=EtY3FTRe; arc=none smtp.client-ip=209.85.210.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="EtY3FTRe" Received: by mail-pf1-f179.google.com with SMTP id d2e1a72fcca58-70d199fb3dfso592941b3a.3 for ; Thu, 25 Jul 2024 02:43:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1721900623; x=1722505423; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=RwdJcLKz/5f8keH5JShytJBM+1xtFuhCZMNTi7Yke18=; b=EtY3FTReEhGMHr3+IagILjbCtnmayu5J8mLdXuxURzwpnx+c8iXaqtSwXG3lFsRe1S 6wyaYV+MmNc9z7iZDSN6IK5ZfA/HKwSyKsKKio2pkyWutdGSaafhw0i0xEZR6z0YWQgu T9S+/S3YL0XHgz6fppuqo/wMr2e4UW2iA+ucm4vUhSw6MufdcwcEogIGm6yzF4tKa5s1 AmSgdteqIhrDNtf63J+ytKjYyNeJ1y9jH78gW8+Gigz7t7jnWKULKlPvHgjJCC7Ws56c EQE/5lZLx8JJ1gnuc5PhV2NCs2kNp33IfCxBwkITzkCCvZs7tX6Blfyz0mUxlcR7kh/4 Ensw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721900623; x=1722505423; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=RwdJcLKz/5f8keH5JShytJBM+1xtFuhCZMNTi7Yke18=; b=EgcQXV2o9aYO+yxopZw+Fi9QhyU6dfoYuun8A9cIyKrP5hpPBokMJ+ZiCL44F6K2Tz oDgN50NpSrWpix2kjwjQmH3YxjnvWZCZJrdRs7RksiJjIJrh/mR+rlbD0udNmLUuCxVK q6sHMXYlFnsSvJgy6oXJPN1MTlFQsfhewibdbsVKzZCZRudNm94EkY2nB+KPTxATK1ZJ f+1+857313f6Cy+jwtBLOduxS5zTLEu0gaJh0QQC4QqTNUZ3BFdmn24rTlS9n4Ng0xGp p6ZtTcVSQ74LKP3beIaiRuenFjVihElC5/glW+kGlfCvGXv2ibGr2VrHA/9MNaIoANMM QQgg== X-Forwarded-Encrypted: i=1; AJvYcCVO7qarLPpfS7HEXZN1snBef/zFkWawBJoo+9SGM12stcnz7nkMvnIgpB9kMy4qoG6KFYlpmKqmb0i7bRARXp9uCsUvCLcutlaAXq7c X-Gm-Message-State: AOJu0YxnRh/6cMbELVgyLtS2xOsPZeZOSFx5iGGWGEEfM38RWV4ss0ac f6R6P941RUEk9J7EN8UWtspdCK9dlHoZ5gIFaC2M1djvVEv62hmEfmQvt5DT6q4= X-Google-Smtp-Source: AGHT+IEVAsa3ZBsFgD39pMLw2LVoMjX7BbCCQjMcMcYrKg6bxSued2Hy0XURQjw7WOeO/dWSuV3Fmg== X-Received: by 2002:a05:6a20:8402:b0:1be:2e2e:5ae8 with SMTP id adf61e73a8af0-1c472ce45c2mr2933218637.40.1721900622845; Thu, 25 Jul 2024 02:43:42 -0700 (PDT) Received: from PXLDJ45XCM.bytedance.net ([139.177.225.254]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fed7ee1477sm10029425ad.169.2024.07.25.02.43.38 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 25 Jul 2024 02:43:42 -0700 (PDT) From: Muchun Song To: hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, akpm@linux-foundation.org, vbabka@kernel.org Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song Subject: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg Date: Thu, 25 Jul 2024 17:43:30 +0800 Message-Id: <20240725094330.72537-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The obj_cgroup_memcg() is supposed to safe to prevent the returned memory cgroup from being freed only when the caller is holding the rcu read lock or objcg_lock or cgroup_mutex. It is very easy to ignore thoes conditions when users call some upper APIs which call obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See the link below). So it is better to add lockdep assertion to obj_cgroup_memcg() to find those issues ASAP. Because there is no user of obj_cgroup_memcg() holding objcg_lock to make the returned memory cgroup safe, do not add objcg_lock assertion (We should export objcg_lock if we really want to do). Additionally, this is some internal implementation detail of memcg and should not be accessible outside memcg code. Some users like __mem_cgroup_uncharge() do not care the lifetime of the returned memory cgroup, which just want to know if the folio is charged to a memory cgroup, therefore, they do not need to hold the needed locks. In which case, introduce a new helper folio_memcg_charged() to do this. Compare it to folio_memcg(), it could eliminate a memory access of objcg->memcg for kmem, actually, a really small gain. Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedan= ce.com/ Signed-off-by: Muchun Song Acked-by: Roman Gushchin Acked-by: Shakeel Butt Acked-by: Vlastimil Babka Tested-by: Marek Szyprowski --- v3: - Use lockdep_assert_once(Vlastimil). v2: - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt). include/linux/memcontrol.h | 20 +++++++++++++++++--- mm/memcontrol.c | 6 +++--- 2 files changed, 20 insertions(+), 6 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index fc94879db4dff..95f823deafeca 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -360,11 +360,11 @@ static inline bool folio_memcg_kmem(struct folio *fol= io); * After the initialization objcg->memcg is always pointing at * a valid memcg, but can be atomically swapped to the parent memcg. * - * The caller must ensure that the returned memcg won't be released: - * e.g. acquire the rcu_read_lock or css_set_lock. + * The caller must ensure that the returned memcg won't be released. */ static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg) { + lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex= )); return READ_ONCE(objcg->memcg); } =20 @@ -438,6 +438,19 @@ static inline struct mem_cgroup *folio_memcg(struct fo= lio *folio) return __folio_memcg(folio); } =20 +/* + * folio_memcg_charged - If a folio is charged to a memory cgroup. + * @folio: Pointer to the folio. + * + * Returns true if folio is charged to a memory cgroup, otherwise returns = false. + */ +static inline bool folio_memcg_charged(struct folio *folio) +{ + if (folio_memcg_kmem(folio)) + return __folio_objcg(folio) !=3D NULL; + return __folio_memcg(folio) !=3D NULL; +} + /** * folio_memcg_rcu - Locklessly get the memory cgroup associated with a fo= lio. * @folio: Pointer to the folio. @@ -454,7 +467,6 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct= folio *folio) unsigned long memcg_data =3D READ_ONCE(folio->memcg_data); =20 VM_BUG_ON_FOLIO(folio_test_slab(folio), folio); - WARN_ON_ONCE(!rcu_read_lock_held()); =20 if (memcg_data & MEMCG_DATA_KMEM) { struct obj_cgroup *objcg; @@ -463,6 +475,8 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct= folio *folio) return obj_cgroup_memcg(objcg); } =20 + WARN_ON_ONCE(!rcu_read_lock_held()); + return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK); } =20 diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 622d4544edd24..3da0284573857 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2366,7 +2366,7 @@ void mem_cgroup_cancel_charge(struct mem_cgroup *memc= g, unsigned int nr_pages) =20 static void commit_charge(struct folio *folio, struct mem_cgroup *memcg) { - VM_BUG_ON_FOLIO(folio_memcg(folio), folio); + VM_BUG_ON_FOLIO(folio_memcg_charged(folio), folio); /* * Any of the following ensures page's memcg stability: * @@ -4617,7 +4617,7 @@ void __mem_cgroup_uncharge(struct folio *folio) struct uncharge_gather ug; =20 /* Don't touch folio->lru of any random page, pre-check: */ - if (!folio_memcg(folio)) + if (!folio_memcg_charged(folio)) return; =20 uncharge_gather_clear(&ug); @@ -4662,7 +4662,7 @@ void mem_cgroup_replace_folio(struct folio *old, stru= ct folio *new) return; =20 /* Page cache replacement: new folio already charged? */ - if (folio_memcg(new)) + if (folio_memcg_charged(new)) return; =20 memcg =3D folio_memcg(old); --=20 2.20.1