that futex bug

[Ben Collins]

Thanks Fabio.

Phillip, can you go ahead and cherry pick this into feisty?

On Sun, 2007-04-22 at 09:15 +0200, Fabio Massimo Di Nitto wrote:
> > commit 21778867b1c8e0feb567addb6dc0a7e2ca6ecdec
> > Author: Ingo Molnar <mingo at elte.hu>
> > Date:   Fri Mar 16 13:38:31 2007 -0800
> > 
> >     [PATCH] futex: PI state locking fix
> >     
> >     Testing of -rt by IBM uncovered a locking bug in
> wake_futex_pi(): the PI
> >     state needs to be locked before we access it.
> >     
> >     Signed-off-by: Ingo Molnar <mingo at elte.hu>
> >     Acked-by: Thomas Gleixner <tglx at linutronix.de>
> >     Cc: Chuck Ebbert <cebbert at redhat.com>
> >     Cc: <stable at kernel.org>
> >     Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> >     Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> > 
> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index e749e7d..5a270b5 100644
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -565,6 +565,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32
> uval, struct futex_q *this)
> >       if (!pi_state)
> >               return -EINVAL;
> >  
> > +     spin_lock(&pi_state->pi_mutex.wait_lock);
> >       new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
> >  
> >       /*
> > @@ -604,6 +605,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32
> uval, struct futex_q *this)
> >       pi_state->owner = new_owner;
> >       spin_unlock_irq(&new_owner->pi_lock);
> >  
> > +     spin_unlock(&pi_state->pi_mutex.wait_lock);
> >       rt_mutex_unlock(&pi_state->pi_mutex);
> >  
> >       return 0;
> 
> 
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