Re: futex breakage in 4.9 stable branch

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, Mar 04 2021 at 10:12, Mike Galbraith wrote:
> On Mon, 2021-03-01 at 18:29 +0100, Ben Hutchings wrote:
>
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -874,8 +874,12 @@ static void free_pi_state(struct futex_p
>  	 * and has cleaned up the pi_state already
>  	 */
>  	if (pi_state->owner) {
> +		unsigned long flags;
> +
> +		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
>  		pi_state_update_owner(pi_state, NULL);
>  		rt_mutex_proxy_unlock(&pi_state->pi_mutex);
> +             raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);

This hunk is missing in 4.9 as well.

>  	}
>
>  	if (current->pi_state_cache)
> @@ -1406,7 +1410,7 @@ static int wake_futex_pi(u32 __user *uad
>  	if (pi_state->owner != current)
>  		return -EINVAL;
>
> -	raw_spin_lock(&pi_state->pi_mutex.wait_lock);
> +	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
>  	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
>
>  	/*

That looks correct.

Thanks,

        tglx