linux-kernel - Re: [RFC][PATCH 2/2] Freezer: Try to handle killable tasks

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Message-ID: <20080519225910.GC2315@elf.ucw.cz>
Date:	Tue, 20 May 2008 00:59:11 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Matthew Wilcox <matthew@....cx>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Cedric Le Goater <clg@...ibm.com>,
	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Liam Howlett <howlett@...il.com>
Subject: Re: [RFC][PATCH 2/2] Freezer: Try to handle killable tasks

On Wed 2008-05-07 20:41:19, Rafael J. Wysocki wrote:
> On Wednesday, 7 of May 2008, Matthew Wilcox wrote:
> > On Wed, May 07, 2008 at 12:07:55AM +0200, Rafael J. Wysocki wrote:
> > > The introduction of TASK_KILLABLE allows the freezer to work in some situation
> > > that it could not handle before.
> > > 
> > > Make the freezer handle killable tasks and add try_to_freeze() in some places
> > > where it is safe to freeze a (killable) task.  Introduce the
> > > wait_event_killable_freezable() macro to be used wherever the freezing of
> > > a waiting killable task is desirable.
> > 
> > Why do you say that TASK_KILLABLE allows the freezer to work in some
> > situations where it couldn't before?  If something's using one of the
> > killable functions, it means that it knows how to clean up and unwind
> > gracefully if the task receives a fatal signal.  I don't understand what
> > connection there is to the freezer.
> 
> The reason why we don't freeze uninterruptible tasks is that we don't know
> why they are in that state.  If one of tasks is uninterruptible for a
> relatively long time, that may indicate a non-recoverable error making it
> dangerous to put the system into a sleep state.  If the task is killable,
> though, the situation is recoverable.

....but the task may still hold some locks, so we can't "just freeze
it".
								Pavel

-- 
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