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

Oliver Neukum
2007-07-05T08:24:32Z

Am Donnerstag, 5. Juli 2007 schrieb Miklos Szeredi:
> > > > 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.

Regards
Oliver