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 5A515C64EC4 for ; Mon, 6 Mar 2023 17:47:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BF77D6B0071; Mon, 6 Mar 2023 12:47:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BA7E96B0072; Mon, 6 Mar 2023 12:47:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A6F816B0073; Mon, 6 Mar 2023 12:47:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 950CB6B0071 for ; Mon, 6 Mar 2023 12:47:09 -0500 (EST) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 75FF6120B70 for ; Mon, 6 Mar 2023 17:47:09 +0000 (UTC) X-FDA: 80539204578.17.5D7661A Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf09.hostedemail.com (Postfix) with ESMTP id A8AA5140026 for ; Mon, 6 Mar 2023 17:47:06 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=R5OU+pfk; spf=pass (imf09.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1678124827; 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=yyo0XeW7H32v2n33gFS+jMOXmRmlgHGjCX1E7zeS1w0=; b=2sVNxZUkwkzoeghb5ZWz6vfNarCsLAMtk9+L8E2RcMjqcj/AsdDSRD9cX+ZD11ymZBdqKt 4kaHVfmSKd1LuA/q7eYEZjNodwrqz4uRuPb5KQY45bgMRVYf361L5B/3Bld91kWH3dIZwa psfQbKNf89BWkTPHJmyMkS8uqIrg25M= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=R5OU+pfk; spf=pass (imf09.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1678124827; a=rsa-sha256; cv=none; b=ehXN6oYtm85wl4Ty9xQR3K65yNgbho3OKK1HTSoVSLlmznHHe0EhkAU1EgqszQexISM1iK f6eRmy+iyYWYNIdPWfX3x13Zn1mDwJQUHSXbR9ZpNUUlLftqPjyr0d7meFcVRB3tpG8sb5 LzXhaQLxjtZ0E/KIJxNHUDAPFn2gwp0= 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 2D91A1FDDD; Mon, 6 Mar 2023 17:47:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1678124825; 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=yyo0XeW7H32v2n33gFS+jMOXmRmlgHGjCX1E7zeS1w0=; b=R5OU+pfkoKfQA+ShDkrA2Ab/7GQX8V5UAbQDog+dOafDsBbUj/UFcnZ9pk4PuaqeDlUO+f oEJZK3fuTgGttOPw1FFsK2b1lsEmqtpmRJraKGUb4fXL/rOpwohtJYV8v2U74LbuU0qxLx 7GQOmS+j6Iq/Ip1rqQ6QQwJHu958cZ8= 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 0F44013513; Mon, 6 Mar 2023 17:47:05 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id rL6vARknBmSSfAAAMHmgww (envelope-from ); Mon, 06 Mar 2023 17:47:05 +0000 Date: Mon, 6 Mar 2023 18:47:04 +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, 1/4] mm, memcg: Prevent memory.oom.group load/store tearing Message-ID: References: <20230306154138.3775-1-findns94@gmail.com> <20230306154138.3775-2-findns94@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230306154138.3775-2-findns94@gmail.com> X-Stat-Signature: b66kq8zb7m1q11et1gqndqzqdixnuyqc X-Rspam-User: X-Rspamd-Queue-Id: A8AA5140026 X-Rspamd-Server: rspam06 X-HE-Tag: 1678124826-282221 X-HE-Meta: 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 6AxQUNuu n53fjRYBDWpMIWXFfHcwsaaBysSTUiNWQwA4c+Y5YVj2f1iwDaiyCcYc3pTHBkSHcyyw9BjsYcP2e3pzKQiWzAoVUMSjBMULchkq+4pbu4CsyUt/HsCzRcaKzcisic/D4kYZA3HxCYRwNRZCAnuCXUI+cCewyoqLuv/KChdNKjTI4SW1q6o2x80rgdk0UjWp/D5DVbffLByoNGwM562Yi5tx7mF32Sge+YbenZDNSe4KE9SafxA+NlYThcw== 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 23:41:35, Yue Zhao wrote: > The knob for cgroup v2 memory controller: memory.oom.group > 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 (the knob is > usually configured long before any workloads hits actual memcg oom) > but it is better to use READ_ONCE/WRITE_ONCE to prevent compiler from > doing anything funky. > > The access of memcg->oom_group is lockless, so it can be > concurrently set at the same time as we are trying to read it. > > Signed-off-by: Yue Zhao Acked-by: Michal Hocko Thanks! > --- > mm/memcontrol.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 5abffe6f8389..06821e5f7604 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2067,7 +2067,7 @@ struct mem_cgroup *mem_cgroup_get_oom_group(struct task_struct *victim, > * highest-level memory cgroup with oom.group set. > */ > for (; memcg; memcg = parent_mem_cgroup(memcg)) { > - if (memcg->oom_group) > + if (READ_ONCE(memcg->oom_group)) > oom_group = memcg; > > if (memcg == oom_domain) > @@ -6623,7 +6623,7 @@ static int memory_oom_group_show(struct seq_file *m, void *v) > { > struct mem_cgroup *memcg = mem_cgroup_from_seq(m); > > - seq_printf(m, "%d\n", memcg->oom_group); > + seq_printf(m, "%d\n", READ_ONCE(memcg->oom_group)); > > return 0; > } > @@ -6645,7 +6645,7 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of, > if (oom_group != 0 && oom_group != 1) > return -EINVAL; > > - memcg->oom_group = oom_group; > + WRITE_ONCE(memcg->oom_group, oom_group); > > return nbytes; > } > -- > 2.17.1 -- Michal Hocko SUSE Labs