linux-kernel - Re: problem 1 (was Re: removing refrigerator does not help with s2ram vs. fuse deadlocks (was Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway))

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Date:	Sat, 7 Jul 2007 22:55:48 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Paul Mackerras <paulus@...ba.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Johannes Berg <johannes@...solutions.net>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: problem 1 (was Re: removing refrigerator does not help with s2ram vs. fuse deadlocks (was Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway))

On Saturday, 7 July 2007 14:08, Pavel Machek wrote:
> Hi!
> 
> > > Now, if kernel needs FUSE services for some reason (that's the problem
> > > we hit in s2ram case, right?), we have a deadlock.
> > > 
> > > So main problem still seems to be "kernel should not depend on
> > > userland services during suspend", refrigerator or not.
> > 
> > And also "Userland should not depend on userland services", which is 
> > rather more of a problem.
> 
> No, that's not a problem. Or rather, that's different problem, called
> "problem 2" (fuse causes freezer to fail to stop processes).
> 
> But we still have "problem 1" here: after devices are suspended,
> kernel tries to use fuse's services. That is not going to work, one
> way or another, because devices are suspended and userland can't work
> reliably.
> 
> (Aha, it _may_ be it is kernel tries to use fuse's services after
> freezing userland but before freezing devices. I don't think it is).
> 
> To solve "problem 1", we need to know which part of kernel asks for
> fuse services. sysrq-t trace is likely to tell us. Can someone repeat
> the "problem 1" scenario (freezer succeeds but then it deadlocks), and
> produce sysrq-t trace? That way we can solve "problem 1".

Well, such a trace would be helpful in any case.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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