Re: [PATCH] pi-futex: set PF_EXITING without taking ->pi_lock

[Ingo Molnar]

* Oleg Nesterov <oleg@xxxxxxxxxx> wrote:

> It is a bit annoying that do_exit() takes ->pi_lock to set PF_EXITING.
> All we need is to synchronize with lookup_pi_state() which saw this task
> without PF_EXITING under ->pi_lock.
> 
> Change do_exit() to use spin_unlock_wait().
> 
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Acked-by: Ingo Molnar <mingo@xxxxxxx>

> -	spin_lock_irq(&tsk->pi_lock);
> -	tsk->flags |= PF_EXITING;
> -	spin_unlock_irq(&tsk->pi_lock);
> +	smp_mb();
> +	spin_unlock_wait(&tsk->pi_lock);

hm, isnt spin_unlock_wait() an SMP barrier in itself? (if not then it 
should be.)

	Ingo
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