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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 35010C43141 for ; Sat, 16 Nov 2019 01:34:46 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id ED0412073C for ; Sat, 16 Nov 2019 01:34:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cQFszwHw" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ED0412073C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9A5046B000A; Fri, 15 Nov 2019 20:34:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 957FB6B000C; Fri, 15 Nov 2019 20:34:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 86C076B000D; Fri, 15 Nov 2019 20:34:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0131.hostedemail.com [216.40.44.131]) by kanga.kvack.org (Postfix) with ESMTP id 72F146B000A for ; Fri, 15 Nov 2019 20:34:45 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 3925A181AEF1E for ; Sat, 16 Nov 2019 01:34:45 +0000 (UTC) X-FDA: 76160421330.28.pig19_c5b364e01b0f X-HE-Tag: pig19_c5b364e01b0f X-Filterd-Recvd-Size: 4058 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Sat, 16 Nov 2019 01:34:44 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 95F91207FA; Sat, 16 Nov 2019 01:34:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573868084; bh=RRKnxqH/UF5xqW+DkjcMaAJpH5mIXzSIhZsl5Lyjvo4=; h=Date:From:To:Subject:From; b=cQFszwHwprJHX1i1mzvfhtKY/0oLTiIhfFhjc23a8UPifuKbfoQ91sFPflFsAKvzh Goe4aJiLPDzhjFMF3zWm4ygg1KTd7m+7YVfJ0cqfN/H/DuZugJI44QwHktD7/fHW9t 6V4+/QtPG4dpjeDhXsefjf/nSVdzVmTOmjIYSfj8= Date: Fri, 15 Nov 2019 17:34:43 -0800 From: akpm@linux-foundation.org To: akpm@linux-foundation.org, guro@fb.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@kernel.org, mkoutny@suse.com, mm-commits@vger.kernel.org, shakeeb@google.com, stable@vger.kernel.org, tj@kernel.org, torvalds@linux-foundation.org Subject: [patch 04/11] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Message-ID: <20191116013443.bdFrXzwW-%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 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: From: Roman Gushchin Subject: mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() 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 ? unix_stream_sendmsg+0x37d/0x3b0 get_signal+0x132/0x7c0 do_signal+0x36/0x640 ? recalc_sigpending+0x17/0x50 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 Cc: Signed-off-by: Andrew Morton --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/memcontrol.c~mm-memcg-switch-to-css_tryget-in-get_mem_cgroup_from_mm +++ a/mm/memcontrol.c @@ -960,7 +960,7 @@ struct mem_cgroup *get_mem_cgroup_from_m if (unlikely(!memcg)) memcg = root_mem_cgroup; } - } while (!css_tryget_online(&memcg->css)); + } while (!css_tryget(&memcg->css)); rcu_read_unlock(); return memcg; } _