From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id E34F26B0032 for ; Wed, 21 Jan 2015 11:40:16 -0500 (EST) Received: by mail-pd0-f175.google.com with SMTP id fl12so17790717pdb.6 for ; Wed, 21 Jan 2015 08:40:16 -0800 (PST) Received: from foss-mx-na.foss.arm.com (foss-mx-na.foss.arm.com. [217.140.108.86]) by mx.google.com with ESMTP id nq15si4287798pdb.212.2015.01.21.08.40.14 for ; Wed, 21 Jan 2015 08:40:15 -0800 (PST) Date: Wed, 21 Jan 2015 16:39:55 +0000 From: Will Deacon Subject: Re: [Regression] 3.19-rc3 : memcg: Hang in mount memcg Message-ID: <20150121163955.GM4549@arm.com> References: <54B01335.4060901@arm.com> <20150110085525.GD2110@esperanza> <54BCFDCF.9090603@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54BCFDCF.9090603@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Suzuki K. Poulose" Cc: Vladimir Davydov , Tejun Heo , Johannes Weiner , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "mhocko@suse.cz" , "akpm@linux-foundation.org" On Mon, Jan 19, 2015 at 12:51:27PM +0000, Suzuki K. Poulose wrote: > On 10/01/15 08:55, Vladimir Davydov wrote: > > The problem is that the memory cgroup controller takes a css reference > > per each charged page and does not reparent charged pages on css > > offline, while cgroup_mount/cgroup_kill_sb expect all css references to > > offline cgroups to be gone soon, restarting the syscall if the ref count > > != 0. As a result, if you create a memory cgroup, charge some page cache > > to it, and then remove it, unmount/mount will hang forever. > > > > May be, we should kill the ref counter to the memory controller root in > > cgroup_kill_sb only if there is no children at all, neither online nor > > offline. > > > > Still reproducible on 3.19-rc5 with the same setup. Yeah, I'm seeing the same failure on my setup too. > From git bisect, the last good commit is : > > commit 8df0c2dcf61781d2efa8e6e5b06870f6c6785735 > Author: Pranith Kumar > Date: Wed Dec 10 15:42:28 2014 -0800 > > slab: replace smp_read_barrier_depends() with lockless_dereference() So that points at 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") as the offending commit. Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org