From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: bind() call in cgroup's css structure Date: Tue, 10 Apr 2012 08:59:33 +0800 Message-ID: <4F8385F5.1020901@huawei.com> References: <4F82EB5C.7090003@parallels.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7BIT Return-path: In-reply-to: <4F82EB5C.7090003-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Glauber Costa Cc: Tejun Heo , Paul Turner , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org" , linux-kernel Glauber Costa wrote: > Hello Tejun, > > During your cgroup refactor, I was wondering if you have any plans to get rid of the bind() callback that is called when hierarchies are moved? I planned to remove it long ago, and Paul M agreed. But after some time, I was trying to make use of it in a patchset, which was used to fix the problem that remount with different subsys bits will fail for !root cgroups. > > At least in tree, there seems to be no users for that. > I actually planned to use it myself, to start or remove a jump label > when cpuacct and cpu cgroups were comounted. > > Problem is, because we have some calls in the cpuset cgroup from inside the cpu hotplug handler, we end up taking the almighty cgroup_mutex from inside the cpu_hotplug.lock. > > jump labels take it in most arches through the get_online_cpus() function call. This means we effectively can't apply jump labels with the cgroup_mutex held, which is the case throughout the whole bind() call. > > All that explained, I figured I might as well ask before I attempted a solution to that myself: as much as populate(), bind seems to be one of the overly complicated callbacks, designed for a scenario in which everything can come and go at will, which is something we're trying to fix. > As we aim for single hierarchy, it defenitely should be removed.