From mboxrd@z Thu Jan 1 00:00:00 1970 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 1C8E9C678D5 for ; Wed, 8 Mar 2023 16:26:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230321AbjCHQ0g (ORCPT ); Wed, 8 Mar 2023 11:26:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39044 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230107AbjCHQ0W (ORCPT ); Wed, 8 Mar 2023 11:26:22 -0500 Received: from mail-qv1-xf34.google.com (mail-qv1-xf34.google.com [IPv6:2607:f8b0:4864:20::f34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1CECAC9A7B; Wed, 8 Mar 2023 08:26:20 -0800 (PST) Received: by mail-qv1-xf34.google.com with SMTP id bo10so11391531qvb.12; Wed, 08 Mar 2023 08:26:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1678292780; h=references:in-reply-to:message-id:date:subject:cc:to:from:from:to :cc:subject:date:message-id:reply-to; bh=pobmz56zWKXlv9VCRaNaOZMVD/RL8QxL/evDPGbbBYE=; b=McRkR1WhMXjVktc5aTw6T5/gz6rhdeR71Ukow2/ZzU1pNGgYskeBNM0STRwyIy0Hfm VTjxzQlU7sNL+v1NTYRQO8byhGn8P2ftwg0bNZl33Yx1hL90jCxOR3bvGXjNkeWh9G+m C3j8eWUiMVJgELYTg2oJkgiUFs3xb8VJ3e0o8SI1++jbALmILsUgu9mjOqkVEbP7RbIl TMWTLq/3F2oYXfLXSG/GLKvyAmjIjvn95772zy1qiECDYhLI3hP7yw575MZeEwjnopoj KCscHtCaCIVPuwZUB7vRCpSp6eQz5bg1OXfrbbiYqWy19G0Ga3XuBmYXT4rGuhEJ20xZ Vryg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678292780; h=references:in-reply-to:message-id:date:subject:cc:to:from :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=pobmz56zWKXlv9VCRaNaOZMVD/RL8QxL/evDPGbbBYE=; b=v9VQlEKSI2hyZCEYmYJJafwLZgPToTwR4sFVRdgWkQFlhLoH6nr/gMkvfxCHFxtJh9 3X+3WPslKFSrccYpN1F7xZ+Ns60jL8HM4BnLFw0aHyeBx13uhsyUJ0w32YGKpg45ZINa eVDpwjaluWg+YVfptCzS2CV73Aq9b7y4Xf9BbJY4zR5Y+6WWf3POb2AgduW+QoLSewVo VMWqaK6+F2KeIKudE91PceATOKe3r+kgDdENn1uChuAKvatcL9AoRfaXxhztrz1+e0yH rbY/el9P6NZZJfL9/4huMA0WBDJxjWZodBjhu4XaIuMlc2uyxpsBxcOrXWlde+GqSBHn Vr0g== X-Gm-Message-State: AO0yUKU7JyHy7dJHaz2YM/M90qKWC1oqe5fJ+APZnK9Mul7kcx5ztLmE /Gc+dzJyJynCKFp5yGLqkbxlL9/lm4La7LN+ X-Google-Smtp-Source: AK7set9fJpkEVxDTECYsrfoWBBWoQm1UPxTBvv9OtImj+CJODpxx724Aby+U/JKlSJDy6TUKlKt6aA== X-Received: by 2002:ad4:5de1:0:b0:56b:f09e:9ab0 with SMTP id jn1-20020ad45de1000000b0056bf09e9ab0mr28752380qvb.5.1678292779760; Wed, 08 Mar 2023 08:26:19 -0800 (PST) Received: from MSI-FindNS.localdomain ([107.191.40.138]) by smtp.gmail.com with ESMTPSA id w20-20020a05620a0e9400b0073b8459d221sm11619813qkm.31.2023.03.08.08.26.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Mar 2023 08:26:19 -0800 (PST) From: Yue Zhao To: akpm@linux-foundation.org Cc: roman.gushchin@linux.dev, hannes@cmpxchg.org, mhocko@kernel.org, shakeelb@google.com, muchun.song@linux.dev, willy@infradead.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, tangyeechou@gmail.com, Yue Zhao Subject: [PATCH v3, 2/4] mm, memcg: Prevent memory.swappiness load/store tearing Date: Thu, 9 Mar 2023 00:25:53 +0800 Message-Id: <20230308162555.14195-3-findns94@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230308162555.14195-1-findns94@gmail.com> References: <20230308162555.14195-1-findns94@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The knob for cgroup v1 memory controller: memory.swappiness is not protected by any locking so it can be modified while it is used. This is not an actual problem because races are unlikely. But it is better to use [READ|WRITE]_ONCE to prevent compiler from doing anything funky. The access of memcg->swappiness and vm_swappiness is lockless, so both of them can be concurrently set at the same time as we are trying to read them. All occurrences of memcg->swappiness and vm_swappiness are updated with [READ|WRITE]_ONCE. Signed-off-by: Yue Zhao --- include/linux/swap.h | 8 ++++---- mm/memcontrol.c | 6 +++--- 2 files changed, 7 insertions(+), 7 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 209a425739a9..3f3fe43d1766 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -620,18 +620,18 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) { /* Cgroup2 doesn't have per-cgroup swappiness */ if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) - return vm_swappiness; + return READ_ONCE(vm_swappiness); /* root ? */ if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg)) - return vm_swappiness; + return READ_ONCE(vm_swappiness); - return memcg->swappiness; + return READ_ONCE(memcg->swappiness); } #else static inline int mem_cgroup_swappiness(struct mem_cgroup *mem) { - return vm_swappiness; + return READ_ONCE(vm_swappiness); } #endif diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 06821e5f7604..1b0112afcad3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4179,9 +4179,9 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css, return -EINVAL; if (!mem_cgroup_is_root(memcg)) - memcg->swappiness = val; + WRITE_ONCE(memcg->swappiness, val); else - vm_swappiness = val; + WRITE_ONCE(vm_swappiness, val); return 0; } @@ -5353,7 +5353,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) #endif page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); if (parent) { - memcg->swappiness = mem_cgroup_swappiness(parent); + WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent)); memcg->oom_kill_disable = parent->oom_kill_disable; page_counter_init(&memcg->memory, &parent->memory); -- 2.17.1