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

Pavel Machek
2007-07-05T22:04:58Z

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
--
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