From nobody Wed Dec 17 09:50:31 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E2000CDB465 for ; Mon, 16 Oct 2023 22:19:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234306AbjJPWTm (ORCPT ); Mon, 16 Oct 2023 18:19:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57394 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234232AbjJPWTg (ORCPT ); Mon, 16 Oct 2023 18:19:36 -0400 Received: from out-204.mta1.migadu.com (out-204.mta1.migadu.com [IPv6:2001:41d0:203:375::cc]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA90FFB for ; Mon, 16 Oct 2023 15:19:33 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1697494772; 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=Ij7CcCAZNuMmzhQYGZQhCh1ZAw1S65+h3j6CiMYYH1k=; b=qe61nNJWgfKNPHV4MWaSLxAEqEn1iXauirsmpPoVE9GASZahjTRawLqTlqdTbyG4eiukfY Lq6KFaL1MtAZvkYpGyYNft0nl3lKbvNndKBxJreTEgFopeQTbNfb5AL+9pAMbJkrsLR2M1 Rt53tdYfBOdP5StnaeY5MmTpUf7UHGw= From: Roman Gushchin To: Andrew Morton Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel@vger.kernel.org, Butt@vger.kernel.org, shakeelb@google.com, Muchun Song , Dennis Zhou , David Rientjes , Vlastimil Babka , Naresh Kamboju , Roman Gushchin Subject: [PATCH v3 4/5] mm: kmem: scoped objcg protection Date: Mon, 16 Oct 2023 15:18:59 -0700 Message-ID: <20231016221900.4031141-5-roman.gushchin@linux.dev> In-Reply-To: <20231016221900.4031141-1-roman.gushchin@linux.dev> References: <20231016221900.4031141-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Switch to a scope-based protection of the objcg pointer on slab/kmem allocation paths. Instead of using the get_() semantics in the pre-allocation hook and put the reference afterwards, let's rely on the fact that objcg is pinned by the scope. It's possible because: 1) if the objcg is received from the current task struct, the task is keeping a reference to the objcg. 2) if the objcg is received from an active memcg (remote charging), the memcg is pinned by the scope and has a reference to the corresponding objcg. Signed-off-by: Roman Gushchin (Cruise) Tested-by: Naresh Kamboju Acked-by: Shakeel Butt Reviewed-by: Vlastimil Babka --- include/linux/memcontrol.h | 9 ++++++++ include/linux/sched/mm.h | 4 ++++ mm/memcontrol.c | 47 ++++++++++++++++++++++++++++++++++++-- mm/slab.h | 15 ++++++------ 4 files changed, 66 insertions(+), 9 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 277690af383d..a89df289144d 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1769,6 +1769,15 @@ bool mem_cgroup_kmem_disabled(void); int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order); void __memcg_kmem_uncharge_page(struct page *page, int order); =20 +/* + * The returned objcg pointer is safe to use without additional + * protection within a scope. The scope is defined either by + * the current task (similar to the "current" global variable) + * or by set_active_memcg() pair. + * Please, use obj_cgroup_get() to get a reference if the pointer + * needs to be used outside of the local scope. + */ +struct obj_cgroup *current_obj_cgroup(void); struct obj_cgroup *get_obj_cgroup_from_current(void); struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio); =20 diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index 8d89c8c4fac1..9a19f1b42f64 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -403,6 +403,10 @@ DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg); * __GFP_ACCOUNT allocations till the end of the scope will be charged to = the * given memcg. * + * Please, make sure that caller has a reference to the passed memcg struc= ture, + * so its lifetime is guaranteed to exceed the scope between two + * set_active_memcg() calls. + * * NOTE: This function can nest. Users must save the return value and * reset the previous value after their own charging scope is over. */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d90cc19e4113..852fe6918f82 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3079,6 +3079,49 @@ __always_inline struct obj_cgroup *get_obj_cgroup_fr= om_current(void) return objcg; } =20 +__always_inline struct obj_cgroup *current_obj_cgroup(void) +{ + struct mem_cgroup *memcg; + struct obj_cgroup *objcg; + + if (in_task()) { + memcg =3D current->active_memcg; + if (unlikely(memcg)) + goto from_memcg; + + objcg =3D READ_ONCE(current->objcg); + if (unlikely((unsigned long)objcg & CURRENT_OBJCG_UPDATE_FLAG)) + objcg =3D current_objcg_update(); + /* + * Objcg reference is kept by the task, so it's safe + * to use the objcg by the current task. + */ + return objcg; + } + + memcg =3D this_cpu_read(int_active_memcg); + if (unlikely(memcg)) + goto from_memcg; + + return NULL; + +from_memcg: + for (; !mem_cgroup_is_root(memcg); memcg =3D parent_mem_cgroup(memcg)) { + /* + * Memcg pointer is protected by scope (see set_active_memcg()) + * and is pinning the corresponding objcg, so objcg can't go + * away and can be used within the scope without any additional + * protection. + */ + objcg =3D rcu_dereference_check(memcg->objcg, 1); + if (likely(objcg)) + break; + objcg =3D NULL; + } + + return objcg; +} + struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio) { struct obj_cgroup *objcg; @@ -3173,15 +3216,15 @@ int __memcg_kmem_charge_page(struct page *page, gfp= _t gfp, int order) struct obj_cgroup *objcg; int ret =3D 0; =20 - objcg =3D get_obj_cgroup_from_current(); + objcg =3D current_obj_cgroup(); if (objcg) { ret =3D obj_cgroup_charge_pages(objcg, gfp, 1 << order); if (!ret) { + obj_cgroup_get(objcg); page->memcg_data =3D (unsigned long)objcg | MEMCG_DATA_KMEM; return 0; } - obj_cgroup_put(objcg); } return ret; } diff --git a/mm/slab.h b/mm/slab.h index 799a315695c6..3d07fb428393 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -484,7 +484,12 @@ static inline bool memcg_slab_pre_alloc_hook(struct km= em_cache *s, if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT)) return true; =20 - objcg =3D get_obj_cgroup_from_current(); + /* + * The obtained objcg pointer is safe to use within the current scope, + * defined by current task or set_active_memcg() pair. + * obj_cgroup_get() is used to get a permanent reference. + */ + objcg =3D current_obj_cgroup(); if (!objcg) return true; =20 @@ -497,17 +502,14 @@ static inline bool memcg_slab_pre_alloc_hook(struct k= mem_cache *s, css_put(&memcg->css); =20 if (ret) - goto out; + return false; } =20 if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s))) - goto out; + return false; =20 *objcgp =3D objcg; return true; -out: - obj_cgroup_put(objcg); - return false; } =20 static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, @@ -542,7 +544,6 @@ static inline void memcg_slab_post_alloc_hook(struct km= em_cache *s, obj_cgroup_uncharge(objcg, obj_full_size(s)); } } - obj_cgroup_put(objcg); } =20 static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab = *slab, --=20 2.42.0