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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86DD2C6FA99 for ; Mon, 6 Mar 2023 17:55:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 081C36B0071; Mon, 6 Mar 2023 12:55:16 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 009616B0072; Mon, 6 Mar 2023 12:55:15 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DEB7D6B0073; Mon, 6 Mar 2023 12:55:15 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id CAE506B0071 for ; Mon, 6 Mar 2023 12:55:15 -0500 (EST) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 83A92A6CCF for ; Mon, 6 Mar 2023 17:55:15 +0000 (UTC) X-FDA: 80539224990.01.01DB1F8 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf05.hostedemail.com (Postfix) with ESMTP id AFCB810000C for ; Mon, 6 Mar 2023 17:55:13 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b="TiNZbQ/P"; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf05.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1678125313; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Aqp8n+ynFi9vKD6/elu4xNwffzRLPo64QpS6Aa5j97A=; b=Jv1R2texhdgl7OoHPesyzn02XtSJSg7RUwnh+xsQ2fBd2wgXg9Q0+fHb9bPqBT969hFVEU O1BSr0Na0PYmrA0tZ4/195VpHI3q6P+W7L7xy01trSqsI5wYbOr3zs2y7WU6AKeRw1J5pz tFppKQlM9H6YeNq79mzFhgNdenRXJo8= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b="TiNZbQ/P"; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf05.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1678125313; a=rsa-sha256; cv=none; b=tZvYBWSLHLCsLk0xewPYmLy9dljwrBt8oR3A4QL8isCcml99jwXXd4tDNbXFKxhxLSO2WE NSYzgoTVMD6LY0uRbYpXr7ozKfy7rx5Zj1sfHsoebFbQyPsj6QfKvwWLm/4DJyJIb1tGzW +GtWE2+c47JGVi4rx/rwFqv4/IBzKgk= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 866081FDEB; Mon, 6 Mar 2023 17:55:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1678125312; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Aqp8n+ynFi9vKD6/elu4xNwffzRLPo64QpS6Aa5j97A=; b=TiNZbQ/PxLX68w8zNSn4wPJDgq8upb8V6Tt94jaRKTf0BYZNGSyPXKcFFpJ6QtTbcJdKga 7SLRqkL+wTzLjA7qEW6sJMYohde4FYtAEzSD0djEAKp1z7kPp9ySONPRSrCmJoZcnB6Baz +A2dH+HFDYlEDKHDbuEm7Hmx/a0Xlzg= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 3E2C813513; Mon, 6 Mar 2023 17:55:12 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 7XTzCwApBmQyAgAAMHmgww (envelope-from ); Mon, 06 Mar 2023 17:55:12 +0000 Date: Mon, 6 Mar 2023 18:55:11 +0100 From: Michal Hocko To: Yue Zhao Cc: akpm@linux-foundation.org, roman.gushchin@linux.dev, hannes@cmpxchg.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 Subject: Re: [PATCH v2, 4/4] mm, memcg: Prevent memory.soft_limit_in_bytes load/store tearing Message-ID: References: <20230306154138.3775-1-findns94@gmail.com> <20230306154138.3775-5-findns94@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230306154138.3775-5-findns94@gmail.com> X-Rspamd-Queue-Id: AFCB810000C X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: tzxb49hyod6rdyo5y9kxjqsoowmyg6tg X-HE-Tag: 1678125313-950731 X-HE-Meta: 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 Ff9eYGGS rjV4AQAAoqfo4qOUOur5g7pzwRPeXSYwB31dACEn+rrhNw8fPSZYOqBNZzZVe/lUNj7lqvIJo+pBHs9JyBAvxhl1pvfXjYez7n0//bkOFdh69NXJ0RDgEaIIb/x9HtpkbuLkYg7n9aLlxL4ubayjcqxg0Yb7KvqNidGgLaCiUAa9dqMBtbmAyGywpOs5tTmrh8AdN19EOpHO/A3VIRA9gkrL46mgTJ5Dim6mKbTq3dLiHOQ0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 06-03-23 23:41:38, Yue Zhao wrote: > 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. Similar here. mem_cgroup_css_reset and mem_cgroup_css_alloc are not covered. > > 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 -- Michal Hocko SUSE Labs