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

[Pavel Machek <pavel@ucw.cz>]

On Thu 2007-07-05 10:17:17, Miklos Szeredi wrote:
> > > > 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. That's very special, and maybe
even a FUSE bug. And that is also what makes FUSE special
w.r.t. s2ram.

So no, you can't claim "FUSE is just IPC". It is very special IPC.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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