From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx205.postini.com [74.125.245.205]) by kanga.kvack.org (Postfix) with SMTP id 6953B6B005D for ; Fri, 20 Jul 2012 15:49:26 -0400 (EDT) Received: by ggm4 with SMTP id 4so5362584ggm.14 for ; Fri, 20 Jul 2012 12:49:25 -0700 (PDT) Date: Fri, 20 Jul 2012 12:49:20 -0700 From: Tejun Heo Subject: Re: [PATCH] cgroup: Don't drop the cgroup_mutex in cgroup_rmdir Message-ID: <20120720194920.GB21218@google.com> References: <87ipdjc15j.fsf@skywalker.in.ibm.com> <1342706972-10912-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1342706972-10912-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: akpm@linux-foundation.org, mhocko@suse.cz, kamezawa.hiroyu@jp.fujitsu.com, liwanp@linux.vnet.ibm.com, lizefan@huawei.com, cgroups@vger.kernel.org, linux-mm@kvack.org On Thu, Jul 19, 2012 at 07:39:32PM +0530, Aneesh Kumar K.V wrote: > From: "Aneesh Kumar K.V" > > We dropped cgroup mutex, because of a deadlock between memcg and cpuset. > cpuset took hotplug lock followed by cgroup_mutex, where as memcg pre_destroy > did lru_add_drain_all() which took hotplug lock while already holding > cgroup_mutex. The deadlock is explained in 3fa59dfbc3b223f02c26593be69ce6fc9a940405 > But dropping cgroup_mutex in cgroup_rmdir also means tasks could get > added to cgroup while we are in pre_destroy. This makes error handling in > pre_destroy complex. So move the unlock/lock to memcg pre_destroy callback. > Core cgroup will now call pre_destroy with cgroup_mutex held. > > Signed-off-by: Aneesh Kumar K.V So, umm, let's not do this at this point. Please just fix memcg such that it doesn't fail ->pre_destroy() and drop subsys->__DEPRECATED_clear_css_refs. cgroup core won't give away new references during or after pre_destroy that way and memcg is the ONLY subsystem needing the deprecated behavior so it's rather counter-productive to implement work-around at this point. Nacked-And-Please-Drop-The-DEPRECATED-Behavior-by: Tejun Heo Thanks. -- tejun -- 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