Re: [patch] futex: PI state locking fix

[Thomas Gleixner <tglx@linutronix.de>]

On Mon, 2007-03-12 at 10:13 +0100, Ingo Molnar wrote:
> Subject: [patch] futex: PI state locking fix
> From: Ingo Molnar <mingo@elte.hu>
> 
> testing of -rt by IBM uncovered a locking bug in wake_futex_pi(): the PI 
> state needs to be locked before we access it.
> 
> this patch has been tested in -rt. Must-have for v2.6.21.
> 
> Signed-off-by: Ingo Molnar <mingo@elte.hu>

Acked-by: Thomas Gleixner <tglx@linutronix.de>

> --
>  kernel/futex.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> Index: linux/kernel/futex.c
> ===================================================================
> --- linux.orig/kernel/futex.c
> +++ linux/kernel/futex.c
> @@ -566,6 +566,7 @@ static int wake_futex_pi(u32 __user *uad
>  	if (!pi_state)
>  		return -EINVAL;
>  
> +	spin_lock(&pi_state->pi_mutex.wait_lock);
>  	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
>  
>  	/*
> @@ -605,6 +606,7 @@ static int wake_futex_pi(u32 __user *uad
>  	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;