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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 053FEC2D0C3 for ; Tue, 17 Dec 2019 00:52:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D920D24673 for ; Tue, 17 Dec 2019 00:52:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727766AbfLQAww (ORCPT ); Mon, 16 Dec 2019 19:52:52 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35564 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727215AbfLQAvp (ORCPT ); Mon, 16 Dec 2019 19:51:45 -0500 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1ih15O-0003PV-08; Tue, 17 Dec 2019 00:51:38 +0000 Received: from ben by deadeye with local (Exim 4.93-RC7) (envelope-from ) id 1ih15L-0005fy-Gg; Tue, 17 Dec 2019 00:51:35 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Shakeel Butt" , "Michal Koutn" , "Johannes Weiner" , "Tejun Heo" , "Linus Torvalds" , "Roman Gushchin" , "Michal Hocko" Date: Tue, 17 Dec 2019 00:47:44 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 130/136] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.80-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Roman Gushchin commit 00d484f354d85845991b40141d40ba9e5eb60faf upstream. We've encountered a rcu stall in get_mem_cgroup_from_mm(): rcu: INFO: rcu_sched self-detected stall on CPU rcu: 33-....: (21000 ticks this GP) idle=6c6/1/0x4000000000000002 softirq=35441/35441 fqs=5017 (t=21031 jiffies g=324821 q=95837) NMI backtrace for cpu 33 <...> RIP: 0010:get_mem_cgroup_from_mm+0x2f/0x90 <...> __memcg_kmem_charge+0x55/0x140 __alloc_pages_nodemask+0x267/0x320 pipe_write+0x1ad/0x400 new_sync_write+0x127/0x1c0 __kernel_write+0x4f/0xf0 dump_emit+0x91/0xc0 writenote+0xa0/0xc0 elf_core_dump+0x11af/0x1430 do_coredump+0xc65/0xee0 get_signal+0x132/0x7c0 do_signal+0x36/0x640 exit_to_usermode_loop+0x61/0xd0 do_syscall_64+0xd4/0x100 entry_SYSCALL_64_after_hwframe+0x44/0xa9 The problem is caused by an exiting task which is associated with an offline memcg. We're iterating over and over in the do {} while (!css_tryget_online()) loop, but obviously the memcg won't become online and the exiting task won't be migrated to a live memcg. Let's fix it by switching from css_tryget_online() to css_tryget(). As css_tryget_online() cannot guarantee that the memcg won't go offline, the check is usually useless, except some rare cases when for example it determines if something should be presented to a user. A similar problem is described by commit 18fa84a2db0e ("cgroup: Use css_tryget() instead of css_tryget_online() in task_get_css()"). Johannes: : The bug aside, it doesn't matter whether the cgroup is online for the : callers. It used to matter when offlining needed to evacuate all charges : from the memcg, and so needed to prevent new ones from showing up, but we : don't care now. Link: http://lkml.kernel.org/r/20191106225131.3543616-1-guro@fb.com Signed-off-by: Roman Gushchin Acked-by: Johannes Weiner Acked-by: Tejun Heo Reviewed-by: Shakeel Butt Cc: Michal Hocko Cc: Michal Koutn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1073,7 +1073,7 @@ static struct mem_cgroup *get_mem_cgroup if (unlikely(!memcg)) memcg = root_mem_cgroup; } - } while (!css_tryget_online(&memcg->css)); + } while (!css_tryget(&memcg->css)); rcu_read_unlock(); return memcg; }