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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 BBFABC5DF60 for ; Thu, 7 Nov 2019 15:44:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 91EE32178F for ; Thu, 7 Nov 2019 15:44:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573141443; bh=tdyLHj6Fb/0NCgSRE+VQacS66eluAgzBSlhZTRwEJFA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=o7rK+hY8au4cWhLT5TfAWRYFIgyurZV8Al5u8ktIb6k3dIbFMmmxyRzq45q7eONTo 4mnVxvl7Q7c3S69BXUKm+obAMBBFzY8IB5lre8YXCyO0hLNiuZYieDAkQI77xnhypP mq7dgzL6KEZQVKvfBvpKxKp4vI9Cy1n6pHkvpd2Y= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388911AbfKGPoD (ORCPT ); Thu, 7 Nov 2019 10:44:03 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:42842 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388901AbfKGPoC (ORCPT ); Thu, 7 Nov 2019 10:44:02 -0500 Received: by mail-qk1-f196.google.com with SMTP id m4so2344339qke.9; Thu, 07 Nov 2019 07:44:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ys9AEr1EzcwNs1Yey+cVVTAWzE2JSG8awKOxUo23hbY=; b=OBKA6wdE/tTZ/oIoiLX0X3PbGgDgehAtEfxoYmVqACsnHlDMhVTnjWyoObP9zA7BnU +loCQUDBGwokaMHGGAGMaQlzlcvrtGCCI2FI4dYXui2DyVw85ZTZEZopMuxPcA27Sp34 Gl5WUT1n/beeZyGkG4N54+0nn98qPbl/Ir0YBEc6NdVFDL83CiFr6W2ONJyemInQdOmu tG8vyOjiOjT/pPc5WcY/qYhFNTU35lN6yHpjjmz3xWq5LLDXWsh316EdeHyMSuGVKHDQ ZQtrLv++5WlZD6aVN4PYJfTTiznoR8preczDSzghd8/yALA6B+Kn9J/VctPveLl0jcoy I+lw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=ys9AEr1EzcwNs1Yey+cVVTAWzE2JSG8awKOxUo23hbY=; b=EFfGytnR43SyyiQYXgdhuAwuF5uOuxXUvXiXl6Ix6D27AXOawmViPLIrCJWPMjhoGR dTAnmjvQH0h3u9vYEPwUQgmO6sa7DvWuhdi1ZOZW6sgh04xWq2XUhfajw480aliNbQ2G X+KiHXZrHYIEuRqF99VwBY//GL7d0biQBYCAfq+d8NNhEUgKGZEh+s/noz9E2Q6R/W4R dvVw7zhF/GGAGP82LxMWPQ8PDMaymw3oGe1zeIqbnysGDLcMYDqHb/ntMA604wV3Uh2U SGqWP2eZF3ejq1yzxWJ6iGa8T+3fkh0D1R08R0qIoyvLAyQ3YpygZJ5ECzYMTp0N5d5F zn2A== X-Gm-Message-State: APjAAAUtMwQp8x6/ZHSg/J2b3Fd996wRm+1fhTz7ziXNEaN0heh7y9fR 34nS52C7A9FQWdD2mxDwl+g= X-Google-Smtp-Source: APXvYqxuKGWyC1WltFUO1XKmb5S5t3VbSp6aWbVPp/B9yDk5w2wfC/6mCIHhJIS/F43O7FzVOfmVbw== X-Received: by 2002:a05:620a:999:: with SMTP id x25mr3557854qkx.189.1573141440343; Thu, 07 Nov 2019 07:44:00 -0800 (PST) Received: from localhost ([2620:10d:c091:500::2:3f13]) by smtp.gmail.com with ESMTPSA id l14sm1305517qkj.61.2019.11.07.07.43.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 Nov 2019 07:43:59 -0800 (PST) Date: Thu, 7 Nov 2019 07:43:58 -0800 From: Tejun Heo To: Roman Gushchin Cc: linux-mm@kvack.org, Andrew Morton , Michal Hocko , Johannes Weiner , linux-kernel@vger.kernel.org, kernel-team@fb.com, stable@vger.kernel.org Subject: Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Message-ID: <20191107154358.GY3622521@devbig004.ftw2.facebook.com> References: <20191106225131.3543616-1-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191106225131.3543616-1-guro@fb.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Nov 06, 2019 at 02:51:30PM -0800, Roman Gushchin wrote: > 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()"). > > Signed-off-by: Roman Gushchin > Cc: stable@vger.kernel.org > Cc: Tejun Heo Acked-by: Tejun Heo Thanks. -- tejun