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

Miklos Szeredi
2007-07-05T08:41:22Z

> > > > > 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.
>
> Then this is a problem specific to fuse. You should teach fuse to block
> suspension while such operations are being performed.

And teach VFS to block suspension, while waiting on a mutex held by
another process performing a fuse operation.

I can already hear the beautiful praise from Al Viro at the sight of
that ;)

Miklos