From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Containers
<containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Paul Menage <paul-inf54ven1CmVyaH7bEyXVA@public.gmane.org>,
Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
"Paul E. McKenney"
<paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
Mandeep Singh Baines
<msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking
Date: Wed, 21 Dec 2011 19:11:01 +0100 [thread overview]
Message-ID: <20111221181101.GA3092@redhat.com> (raw)
In-Reply-To: <20111221175943.GG17668@somewhere>
On 12/21, Frederic Weisbecker wrote:
>
> On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
> > On 12/21, Frederic Weisbecker wrote:
> > > - By the time we call cgroup_post_fork(), it is ready to be woken up
> > > and usable by the scheduler.
> >
> > No, the new child can't run until do_fork()->wake_up_new_task().
>
> Out of curiosity, why is it not possible for a task to kill and wake up the child
> before that happens?
Because it is not possible to wake it up.
Please note that copy_process() creates the "deactivated" child, iow
it is not on rq.
But, at the same time its ->state == TASK_RUNNING. This "fools"
try_to_wake_up() or anything else which in theory could place it
on the runqueue.
Except, of course, wake_up_new_task() does activate_task(). And
note that it does this unconditionally, exactly because we know that
this task can't be woken.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>, Tejun Heo <tj@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Mandeep Singh Baines <msb@chromium.org>,
Containers <containers@lists.linux-foundation.org>,
Cgroups <cgroups@vger.kernel.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Paul Menage <paul@paulmenage.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking
Date: Wed, 21 Dec 2011 19:11:01 +0100 [thread overview]
Message-ID: <20111221181101.GA3092@redhat.com> (raw)
In-Reply-To: <20111221175943.GG17668@somewhere>
On 12/21, Frederic Weisbecker wrote:
>
> On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
> > On 12/21, Frederic Weisbecker wrote:
> > > - By the time we call cgroup_post_fork(), it is ready to be woken up
> > > and usable by the scheduler.
> >
> > No, the new child can't run until do_fork()->wake_up_new_task().
>
> Out of curiosity, why is it not possible for a task to kill and wake up the child
> before that happens?
Because it is not possible to wake it up.
Please note that copy_process() creates the "deactivated" child, iow
it is not on rq.
But, at the same time its ->state == TASK_RUNNING. This "fools"
try_to_wake_up() or anything else which in theory could place it
on the runqueue.
Except, of course, wake_up_new_task() does activate_task(). And
note that it does this unconditionally, exactly because we know that
this task can't be woken.
Oleg.
next prev parent reply other threads:[~2011-12-21 18:11 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-21 3:43 Q: cgroup: Questions about possible issues in cgroup locking Frederic Weisbecker
2011-12-21 3:43 ` Frederic Weisbecker
2011-12-21 13:08 ` Oleg Nesterov
2011-12-21 13:08 ` Oleg Nesterov
[not found] ` <20111221130848.GA19679-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2011-12-21 17:56 ` Frederic Weisbecker
2011-12-21 17:56 ` Frederic Weisbecker
2011-12-21 19:01 ` Mandeep Singh Baines
2011-12-21 19:01 ` Mandeep Singh Baines
[not found] ` <20111221190102.GE13529-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2011-12-21 19:08 ` Frederic Weisbecker
2011-12-21 19:08 ` Frederic Weisbecker
2011-12-21 19:24 ` Mandeep Singh Baines
2011-12-21 19:24 ` Mandeep Singh Baines
[not found] ` <20111221192413.GF13529-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2011-12-21 20:04 ` Frederic Weisbecker
2011-12-21 20:04 ` Frederic Weisbecker
2011-12-22 15:30 ` Oleg Nesterov
2011-12-22 15:30 ` Oleg Nesterov
[not found] ` <20111222153004.GA30522-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-04 19:36 ` Mandeep Singh Baines
2012-01-04 19:36 ` Mandeep Singh Baines
[not found] ` <20120104193614.GF9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-06 15:23 ` Oleg Nesterov
2012-01-06 15:23 ` Oleg Nesterov
[not found] ` <20120106152356.GA23995-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-06 18:25 ` Mandeep Singh Baines
2012-01-06 18:25 ` Mandeep Singh Baines
2012-01-06 18:25 ` Mandeep Singh Baines
[not found] ` <20120106182535.GJ9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-11 16:07 ` Oleg Nesterov
2012-01-11 16:07 ` Oleg Nesterov
[not found] ` <20120111160730.GA24556-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-12 0:31 ` Mandeep Singh Baines
2012-01-12 0:31 ` Mandeep Singh Baines
[not found] ` <20120112003102.GB9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-12 17:07 ` Oleg Nesterov
2012-01-12 17:07 ` Oleg Nesterov
[not found] ` <20120112170728.GA25717-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-12 17:57 ` Mandeep Singh Baines
2012-01-12 17:57 ` Mandeep Singh Baines
2012-01-12 17:57 ` Mandeep Singh Baines
[not found] ` <20120112175725.GD9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-13 15:20 ` Oleg Nesterov
2012-01-13 15:20 ` Oleg Nesterov
[not found] ` <20120113152010.GA19215-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-13 18:27 ` Mandeep Singh Baines
2012-01-13 18:27 ` Mandeep Singh Baines
[not found] ` <20120113182750.GD18166-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-14 17:36 ` Oleg Nesterov
2012-01-14 17:36 ` Oleg Nesterov
[not found] ` <20120114173648.GA32543-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-18 23:17 ` Mandeep Singh Baines
2012-01-18 23:17 ` Mandeep Singh Baines
2012-01-18 23:17 ` Mandeep Singh Baines
2012-01-19 15:45 ` Oleg Nesterov
[not found] ` <20120119154522.GA14058-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-01-19 18:18 ` Mandeep Singh Baines
2012-01-19 18:18 ` Mandeep Singh Baines
[not found] ` <20120119181803.GU18166-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-20 15:06 ` Oleg Nesterov
2012-01-20 15:06 ` Oleg Nesterov
2012-01-19 18:18 ` Mandeep Singh Baines
2012-03-20 19:34 ` Oleg Nesterov
2012-03-20 19:34 ` Oleg Nesterov
[not found] ` <20120320193414.GA21277-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2012-03-21 18:59 ` Mandeep Singh Baines
2012-03-21 18:59 ` Mandeep Singh Baines
[not found] ` <20120321185955.GK27051-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-03-23 17:51 ` Oleg Nesterov
2012-03-23 17:51 ` Oleg Nesterov
2012-03-23 17:51 ` Oleg Nesterov
2012-03-20 19:34 ` Oleg Nesterov
[not found] ` <20120118231742.GS18166-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-01-19 15:45 ` Oleg Nesterov
2012-01-04 19:36 ` Mandeep Singh Baines
2011-12-22 15:30 ` Oleg Nesterov
2011-12-21 20:04 ` Frederic Weisbecker
2011-12-21 19:01 ` Mandeep Singh Baines
2011-12-21 17:56 ` Frederic Weisbecker
2011-12-21 17:59 ` Frederic Weisbecker
2011-12-21 17:59 ` Frederic Weisbecker
2011-12-21 18:11 ` Oleg Nesterov [this message]
2011-12-21 18:11 ` Oleg Nesterov
[not found] ` <20111221181101.GA3092-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2011-12-21 18:23 ` Frederic Weisbecker
2011-12-21 18:23 ` Frederic Weisbecker
2011-12-21 18:23 ` Frederic Weisbecker
2012-02-01 16:28 ` Frederic Weisbecker
2012-02-01 16:28 ` Frederic Weisbecker
2012-02-01 16:28 ` Frederic Weisbecker
2011-12-21 13:08 ` Oleg Nesterov
-- strict thread matches above, loose matches on Subject: below --
2011-12-21 3:43 Frederic Weisbecker
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