Re: [-rt] Fix race condition and following BUG in PI-futex

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 2006-08-01 at 13:22 -0700, Darren Hart wrote:

> > >
> > >   	list_del_init(&pi_state->owner->pi_state_list);
> > >   	list_add(&pi_state->list, &new_owner->pi_state_list);
> > >   	pi_state->owner = new_owner;
> > > +	atomic_inc(&pi_state->refcount);
> >
> > There really needs to be a get_pi_state() or some variant. Having to do
> > a manual atomic_inc is very dangerous.
> 
> I understand the need to grab the wait_lock in order to serialize 
> rt_mutex_next_owner(), but why the addition of of the atomic_inc() and the 
> free_pi_state() ?  And if we do need them, shouldn't we place them around the 
> use of the pi_state, rather than just before the unlock calls?

Hmm, is the inc really needed?  The hb->lock is held through this and
the pi_state can't go away while that lock is held.

-- Steve