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

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > > 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.

I think you want to stick try_to_freeze() at the same places where you
do SIGKILL handling. That should solve the 'syslogd is unfreezeable'
problem.

Plus, it would be nice to find out where suspend/hibernation is
triggering fuse activity. We can then decide where to fix it -- in
fuse or in suspend parts. You said sys_sync is not implemented... so
where is the problem?

> > That's very special, and maybe even a FUSE bug. And that is also
> > what makes FUSE special w.r.t. s2ram.
> 
> What makes fuse special is that some file operations are synchronous
> and non-restartable.  That's just how the UNIX filesystem API works
> and is hardly a bug in fuse.

Well, unix is not plan9, and maybe userland filesystems are impossible
in unix. But that is hardly a bug in unix :-).

							Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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