linux-kernel - Re: freezer problems

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Message-Id: <200702181914.45757.rjw@sisk.pl>
Date:	Sun, 18 Feb 2007 19:14:44 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	ego@...ibm.com, akpm@...l.org, paulmck@...ibm.com, mingo@...e.hu,
	vatsa@...ibm.com, dipankar@...ibm.com,
	venkatesh.pallipadi@...el.com, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>
Subject: Re: freezer problems

On Sunday, 18 February 2007 17:19, Oleg Nesterov wrote:
> On 02/18, Rafael J. Wysocki wrote:
> >
> > On Sunday, 18 February 2007 15:52, Oleg Nesterov wrote:
> > > 
> > > 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.
> > 
> > Hm, I haven't been aware of this case.
> > 
> > Well, probably we can do something like in the patch that I've just sent: the
> > child that enters the refrigerator should know that the parent is
> > uninterruptible and will wait for it to exit.  Thus it can either mark the
> > parent as frozen or just exit the refrigerator without freezing itself.
> 
> Sub-thread could already sleep in refrigerator when another thread does exec.
> So we have no choice but somehow freeze the execer. But again, I don't know
> if it is safe to freeze it here, at de_thread() stage. It is called from
> load_xxx_binary(), we may hold some important locks...

So it probably isn't safe.

Rafael

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