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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7DE3C4338F for ; Fri, 30 Jul 2021 06:44:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3EBAE61008 for ; Fri, 30 Jul 2021 06:44:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3EBAE61008 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id D47986B0036; Fri, 30 Jul 2021 02:44:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CF6496B005D; Fri, 30 Jul 2021 02:44:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BE4576B006C; Fri, 30 Jul 2021 02:44:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0153.hostedemail.com [216.40.44.153]) by kanga.kvack.org (Postfix) with ESMTP id A3A3D6B0036 for ; Fri, 30 Jul 2021 02:44:36 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 44359184796BD for ; Fri, 30 Jul 2021 06:44:36 +0000 (UTC) X-FDA: 78418315752.01.890CFD4 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf07.hostedemail.com (Postfix) with ESMTP id 8F8821003345 for ; Fri, 30 Jul 2021 06:44:35 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 3DB0F1FDB2; Fri, 30 Jul 2021 06:44:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1627627474; 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=mi1HYsWpUJ4quInI70i8clFEb3QGaTP2cyfGUhAVlYg=; b=QZac1o24u01b6AgmLK3Z0+E0zMc4ZqY4IyVVXaXxctxAv00rJsz5IuS5BFlXoC+VYRlBGS zzqVQeD7TgrhHa9bFg3NEGMvyMvwrwKz87Izv/ltThmf5cUZYq9CpmqrBKO3fyKsJWaDam pLTUGlKfs0yq3HNIhQLIOGfvmfv+i+M= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id DE133A3B8B; Fri, 30 Jul 2021 06:44:33 +0000 (UTC) Date: Fri, 30 Jul 2021 08:44:33 +0200 From: Michal Hocko To: Roman Gushchin Cc: Miaohe Lin , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, shakeelb@google.com, willy@infradead.org, alexs@kernel.org, richard.weiyang@gmail.com, songmuchun@bytedance.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() Message-ID: References: <20210729125755.16871-1-linmiaohe@huawei.com> <20210729125755.16871-5-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=QZac1o24; spf=pass (imf07.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 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8F8821003345 X-Stat-Signature: bmz3n65fjmr1i6o643zparbmg9zyggfg X-HE-Tag: 1627627475-832281 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 Thu 29-07-21 20:12:43, Roman Gushchin wrote: > On Thu, Jul 29, 2021 at 08:57:54PM +0800, Miaohe Lin wrote: > > rtpn might be NULL in very rare case. We have better to check it before > > dereferencing it. Since memcg can live with NULL rb_tree_per_node in > > soft_limit_tree, warn this case and continue. > > > > Signed-off-by: Miaohe Lin > > --- > > mm/memcontrol.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 5b4592d1e0f2..70a32174e7c4 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -7109,6 +7109,8 @@ static int __init mem_cgroup_init(void) > > rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, > > node_online(node) ? node : NUMA_NO_NODE); > > > > + if (WARN_ON_ONCE(!rtpn)) > > + continue; > > I also really doubt that it makes any sense to continue in this case. > If this allocations fails (at the very beginning of the system's life, it's an __init function), > something is terribly wrong and panic'ing on a NULL-pointer dereference sounds like > a perfect choice. Moreover this is 24B allocation during early boot. Kernel will OOM and panic when not being able to find any victim. I do not think we need to do any special handling here. -- Michal Hocko SUSE Labs