linux-kernel - Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Message-ID: <20070705220444.GD3881@elf.ucw.cz>
Date:	Fri, 6 Jul 2007 00:04:44 +0200
From:	Pavel Machek <pavel@....cz>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	oliver@...kum.org, paulus@...ba.org, stern@...land.harvard.edu,
	johannes@...solutions.net, rjw@...k.pl,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	mjg59@...f.ucam.org, benh@...nel.crashing.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

Hi!

> > > > > > I have discussed the benefits elsewhere.  As for the deadlocks -- do 
> > > > > > you still observe them if you use the version of the freezer which 
> > > > > > doesn't freeze kernel threads?
> > > > > 
> > > > > In general the only way to guarantee there are no deadlocks is to
> > > > > construct the graph of dependencies between tasks.  Those dependencies
> > > > > are not in practice observable from outside the tasks, so it is
> > > > > virtually impossible to construct the graph.
> > > > 
> > > > In which way can user space tasks depend on each other in a way that
> > > > allows a them members of that cycle to be in uninterruptible sleep?
> > > 
> > >  - process A calls rename() on a fuse fs
> > >  - process B, the fuse server, starts to process the rename request
> > >  - process B is frozen before it can reply
> > > 
> > > Now process A is unfreezable.  We cannot make rename() restartable,
> > > hence it cannot be interruptible.
> > 
> > Yes, we are claiming fuse is very special in this regard, and perhaps
> > even broken.
> > 
> > Let's see. If I SIGSTOP the fuse server, I can get unrelated tasks
> > unkillable (even for SIGKILL!) forever.
> 
> Actually fuse allows SIGKILL, because it's always fatal, and the
> syscall may not be restarted.

Okay, and you should handle refrigerator in the same paths where you
handle SIGKILL. Just add try_to_freeze() there...
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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