From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH v2 1/1] freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() Date: Fri, 26 Oct 2012 10:52:58 -0700 Message-ID: <20121026175258.GV11442@htj.dyndns.org> References: <20121022211317.GD5951@atj.dyndns.org> <20121023153919.GA16201@redhat.com> <20121024185710.GA12182@atj.dyndns.org> <20121025163941.GA3801@redhat.com> <20121025163959.GB3801@redhat.com> <20121025171812.GE11442@htj.dyndns.org> <20121025173433.GA7650@redhat.com> <20121025173632.GI11442@htj.dyndns.org> <20121026174545.GA21639@redhat.com> <20121026174606.GB21639@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20121026174606.GB21639-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 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: Oleg Nesterov Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, rjw-KKrjLPT3xs0@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.vger.kernel.org On Fri, Oct 26, 2012 at 07:46:06PM +0200, Oleg Nesterov wrote: > try_to_freeze_tasks() and cgroup_freezer rely on scheduler locks > to ensure that a task doing STOPPED/TRACED -> RUNNING transition > can't escape freezing. This mostly works, but ptrace_stop() does > not necessarily call schedule(), it can change task->state back to > RUNNING and check freezing() without any lock/barrier in between. > > We could add the necessary barrier, but this patch changes > ptrace_stop() and do_signal_stop() to use freezable_schedule(). > This fixes the race, freezer_count() and freezer_should_skip() > carefully avoid the race. > > And this simplifies the code, try_to_freeze_tasks/update_if_frozen > no longer need to use task_is_stopped_or_traced() checks with the > non trivial assumptions. We can rely on the mechanism which was > specially designed to mark the sleeping task as "frozen enough". > > v2: As Tejun pointed out, we can also change get_signal_to_deliver() > and move try_to_freeze() up before 'relock' label. > > Signed-off-by: Oleg Nesterov Looks good to me. :) Acked-by: Tejun Heo Rafael, sorry that this one doesn't have pm cc'd but can you please pick up this one too? Thanks a lot. -- tejun