From: Oleg Nesterov <oleg@tv-sign.ru>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: ego@in.ibm.com, akpm@osdl.org, paulmck@us.ibm.com, mingo@elte.hu,
vatsa@in.ibm.com, dipankar@in.ibm.com,
venkatesh.pallipadi@intel.com, linux-kernel@vger.kernel.org,
Pavel Machek <pavel@ucw.cz>
Subject: freezer problems
Date: Sun, 18 Feb 2007 17:52:46 +0300 [thread overview]
Message-ID: <20070218145246.GA80@tv-sign.ru> (raw)
In-Reply-To: <200702181314.29214.rjw@sisk.pl>
On 02/18, Rafael J. Wysocki wrote:
>
> On Sunday, 18 February 2007 12:31, Oleg Nesterov wrote:
> > > >
> > > > However, this means that sys_vfork() makes impossible to freeze processes
> > > > until child exits/execs. Not good.
> > >
> > I forgot to say that we have another problem: coredumping.
> >
> > A thread which does do_coredump() send SIGKILL to ->mm users, and sleeps
> > on ->mm->core_startup_done. Now it can't be frozen if sub-thread goes to
> > refrigerator. I think this could be solved easily if we add a check to
> > refrigerator() as you suggested for ->vfork_donw.
> >
> > > I think the real solution would be to use an interruptible completion in the
> > > vfork code. It was discussed some time ago and, IIRC, Ingo had an experimental
> > > patch that implemented it. Still, for the suspend this really is not an issue
> > > in practice, so it wasn't merged.
> >
> > It is not (afaics) so trivial to do rightly, and with this change the parent
> > will be seen as TASK_INTERRUPTIBLE even without freezer in progress.
> >
> > A very vague idea: what if parent will do
> >
> > current->flags |= PF_PLEASE_CONSIDER_ME_AS_FROZEN_BUT_SET_TIF_FREEZE
> > wait_for_completion(&vfork);
> > try_to_freeze();
> >
> > ?
>
> This should work,
Good. So try_to_freeze_tasks() can forget about "if (!p->vfork_done)" check.
This needs more thinking, of course. For example, thaw_process() should be
carefull to clear TIF_FREEZE if we have the new flag set, but not PF_FROZEN.
frozen() should be changed to return true if PF_NEW_FLAG && TIF_FREEZE, but
it also called by refrigerator.
But IF we really can do this, it will be a general solution.
> but we'll need a separate process flag for it. If that's
> acceptable,
I can't judge. Changed the subject to have more attention from experts.
> I'd call it PF_VFORK_PARENT
I'd suggest not to put "VFORK" into the name. Probably we will find other
usage for this flag which in fact means: "I am sleeping TASK_UNINTERRUPTIBLE
at the safe place to freeze, I promise to do try_to_freeze() when I have
CPU".
And now another problem: exec. de_thread() sleeps in TASK_UNINTERRUPTIBLE
waiting for all sub-threads to die, and we have the same "deadlock" if
one of them is frozen. This is nasty. Probably we can change the ->state
to TASK_INTERRUPTIBLE and add try_to_freeze(), or play with the new PF_
flag, but I am not sure it is safe to freeze() the task which is deep
in the exec() path.
Oleg.
next prev parent reply other threads:[~2007-02-18 14:50 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-14 14:40 [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Gautham R Shenoy
2007-02-14 14:42 ` [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core Gautham R Shenoy
2007-02-14 14:43 ` [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c Gautham R Shenoy
2007-02-14 14:43 ` [RFC PATCH(Experimental) 3/4] Revert changes to sched.c and slab.c Gautham R Shenoy
2007-02-14 14:44 ` [RFC PATCH(Experimental) 4/4] Rip out lock_cpu_hotplug from linux Gautham R Shenoy
2007-02-14 14:59 ` [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c Srivatsa Vaddagiri
2007-02-14 15:24 ` Srivatsa Vaddagiri
2007-02-14 20:23 ` Oleg Nesterov
2007-02-14 20:09 ` Oleg Nesterov
2007-02-16 5:26 ` Srivatsa Vaddagiri
2007-02-16 15:33 ` Oleg Nesterov
2007-02-16 16:47 ` Srivatsa Vaddagiri
2007-02-16 18:45 ` Oleg Nesterov
2007-02-16 23:59 ` Oleg Nesterov
2007-02-17 2:29 ` Srivatsa Vaddagiri
2007-02-17 21:59 ` Oleg Nesterov
2007-02-20 15:12 ` Srivatsa Vaddagiri
2007-02-20 20:09 ` Oleg Nesterov
2007-02-21 6:29 ` Srivatsa Vaddagiri
2007-02-21 14:30 ` Oleg Nesterov
2007-02-21 14:37 ` Gautham R Shenoy
2007-02-21 15:53 ` Srivatsa Vaddagiri
2007-02-14 15:31 ` [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core Srivatsa Vaddagiri
2007-02-14 19:47 ` Oleg Nesterov
2007-02-16 6:48 ` Srivatsa Vaddagiri
2007-02-16 15:47 ` Oleg Nesterov
2007-02-14 20:22 ` Oleg Nesterov
2007-02-16 7:16 ` Srivatsa Vaddagiri
2007-02-16 8:12 ` Srivatsa Vaddagiri
2007-02-16 9:29 ` Rafael J. Wysocki
2007-02-16 9:59 ` Srivatsa Vaddagiri
2007-02-16 11:06 ` Rafael J. Wysocki
2007-02-16 19:46 ` Oleg Nesterov
2007-02-17 2:31 ` Srivatsa Vaddagiri
2007-02-17 5:32 ` Gautham R Shenoy
2007-02-17 11:19 ` Gautham R Shenoy
2007-02-16 16:06 ` Oleg Nesterov
2007-02-14 21:43 ` [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Rafael J. Wysocki
2007-02-15 6:34 ` Gautham R Shenoy
2007-02-15 8:09 ` Rafael J. Wysocki
2007-02-15 12:20 ` Gautham R Shenoy
2007-02-15 13:31 ` Rafael J. Wysocki
2007-02-15 14:25 ` Gautham R Shenoy
2007-02-17 11:24 ` Rafael J. Wysocki
2007-02-17 21:34 ` Oleg Nesterov
2007-02-17 22:24 ` Rafael J. Wysocki
2007-02-17 23:42 ` Oleg Nesterov
2007-02-17 23:47 ` Oleg Nesterov
2007-02-18 10:43 ` Rafael J. Wysocki
2007-02-18 11:31 ` Oleg Nesterov
2007-02-18 12:14 ` Rafael J. Wysocki
2007-02-18 14:52 ` Oleg Nesterov [this message]
2007-02-18 15:14 ` freezer problems Rafael J. Wysocki
2007-02-18 16:19 ` Oleg Nesterov
2007-02-18 18:14 ` Rafael J. Wysocki
2007-02-18 18:56 ` Rafael J. Wysocki
2007-02-18 22:01 ` Oleg Nesterov
2007-02-18 23:19 ` Rafael J. Wysocki
2007-02-19 20:23 ` Oleg Nesterov
2007-02-19 21:21 ` Rafael J. Wysocki
2007-02-19 22:41 ` Oleg Nesterov
2007-02-19 23:35 ` Rafael J. Wysocki
2007-02-20 0:12 ` Oleg Nesterov
2007-02-20 0:32 ` Rafael J. Wysocki
2007-02-20 0:50 ` Oleg Nesterov
2007-02-20 18:28 ` Rafael J. Wysocki
2007-02-20 18:29 ` Rafael J. Wysocki
2007-02-21 18:14 ` Paul E. McKenney
2007-02-21 18:13 ` Rafael J. Wysocki
2007-02-21 18:27 ` Paul E. McKenney
2007-02-21 20:03 ` Oleg Nesterov
2007-02-21 20:47 ` Rafael J. Wysocki
2007-02-21 21:06 ` Paul E. McKenney
2007-02-21 23:10 ` Rafael J. Wysocki
2007-02-22 10:47 ` Oleg Nesterov
2007-02-22 11:33 ` Oleg Nesterov
2007-02-22 17:03 ` Rafael J. Wysocki
2007-02-22 17:44 ` Oleg Nesterov
2007-02-22 21:56 ` Rafael J. Wysocki
2007-02-23 18:15 ` Oleg Nesterov
2007-02-23 3:02 ` Gautham R Shenoy
2007-02-18 15:09 ` [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Rafael J. Wysocki
2007-02-18 16:11 ` Oleg Nesterov
2007-02-18 18:51 ` Rafael J. Wysocki
2007-02-18 10:32 ` Rafael J. Wysocki
2007-02-18 11:32 ` Oleg Nesterov
2007-02-18 12:12 ` Rafael J. Wysocki
2007-02-18 15:06 ` Oleg Nesterov
2007-02-18 12:56 ` Pavel Machek
2007-02-21 14:52 ` Gautham R Shenoy
2007-02-21 19:42 ` Pavel Machek
[not found] ` <200702231041.17136.rjw@sisk.pl>
[not found] ` <20070223100817.GA10973@in.ibm.com>
[not found] ` <200702231115.00718.rjw@sisk.pl>
[not found] ` <20070223104723.GB10973@in.ibm.com>
[not found] ` <20070223110201.GC10973@in.ibm.com>
2007-02-23 19:03 ` freezer problems Gautham R Shenoy
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