From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: Is not locking task_lock in cgroup_fork() safe? Date: Tue, 16 Oct 2012 12:34:28 -0700 Message-ID: <20121016193428.GE16166@google.com> References: <20121008020000.GB2575@localhost> <20121008020138.GA4188@localhost> <507268AA.8050509@huawei.com> <20121008065752.GA5931@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20121008065752.GA5931@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Li Zefan Cc: Frederic Weisbecker , containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.vger.kernel.org On Mon, Oct 08, 2012 at 03:57:52PM +0900, Tejun Heo wrote: > Hello, Li, Frederic. > > On Mon, Oct 08, 2012 at 01:46:18PM +0800, Li Zefan wrote: > > You're right. threadgroup lock is held unconditionally in attach_task_py_pid(), > > but it's held only for CLONE_THREAD in fork path, which I guess I overlooked > > when reviewing the patch. > > > > > Also, please note that task_lock is likely to be hot on local CPU at > > > that point and avoiding it there might not really buy much. > > > > Reverting that commit should be fine. > > There are other commits which perform similar optimization > > 7e3aa30ac8 ("cgroup: Remove task_lock() from cgroup_post_fork()") > c84cdf75cc ("cgroup: Remove unnecessary task_lock before fetching css_set on migration") > > Are they wrong too? Frederic, Li, Ping? Thanks. -- tejun