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

Pavel Machek
2007-07-05T09:18:17Z

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
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