From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yue Zhao Subject: [PATCH v2, 4/4] mm, memcg: Prevent memory.soft_limit_in_bytes load/store tearing Date: Mon, 6 Mar 2023 23:41:38 +0800 Message-ID: <20230306154138.3775-5-findns94@gmail.com> References: <20230306154138.3775-1-findns94@gmail.com> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1678117341; h=references:in-reply-to:message-id:date:subject:cc:to:from:from:to :cc:subject:date:message-id:reply-to; bh=kK+Z862YESi30yZiQZC0bVwPclz8DCYbgAA/NRofcVQ=; b=MQT4Hnfv44YHIOGxCsajlC63JnDzxTzHLtNuHQ/4uiD559rPdzNVrnv4Px3cAWbxDT mINlBKvoJaziRxF2qQ48A+vB+8zsxIWkAgcnn431o0fdeuq+YmC8FrPglq91Yb0DDBkJ WCLdr+wil1dX/B6cEeylUBOsYJhZePeAW3jZ1aJkQWk2cbXPdeqFFkZtLAxMl1FEsIxI ZOYN/pszFbWfajWHX+xyZoGuf9/U9Vv9ybClKwIRhxirENLM5KmkGZl7e3gna1SBvxIm JgGvX3aNy1f0bzrfeRrAG0+mzAEsXE05Es60AK0gbwyXOMMURS2NJzZ+Y2ZsdTWsYAeT IXVA== In-Reply-To: <20230306154138.3775-1-findns94-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org Cc: roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, muchun.song-fxUVXftIFDnyG1zEObXtfA@public.gmane.org, willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tangyeechou-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Yue Zhao The knob for cgroup v1 memory controller: memory.soft_limit_in_bytes 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_ONCE/WRITE_ONCE to prevent compiler from doing anything funky. The access of memcg->soft_limit is lockless, so it can be concurrently set at the same time as we are trying to read it. Signed-off-by: Yue Zhao --- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 26605b2f51b1..20566f59bbcb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3728,7 +3728,7 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css, case RES_FAILCNT: return counter->failcnt; case RES_SOFT_LIMIT: - return (u64)memcg->soft_limit * PAGE_SIZE; + return (u64)READ_ONCE(memcg->soft_limit) * PAGE_SIZE; default: BUG(); } @@ -3870,7 +3870,7 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of, if (IS_ENABLED(CONFIG_PREEMPT_RT)) { ret = -EOPNOTSUPP; } else { - memcg->soft_limit = nr_pages; + WRITE_ONCE(memcg->soft_limit, nr_pages); ret = 0; } break; -- 2.17.1