Re: [PATCH] fix refrigerator() vs thaw_process() race

[Oleg Nesterov]

On 02/19, Pavel Machek wrote:
> 
> > refrigerator() can miss a wakeup, "wait event" loop needs a proper memory
> > ordering.
> > 
> > Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
> > 
> > --- WQ/kernel/power/process.c~WAKE  2007-02-18 22:56:49.000000000 +0300
> > +++ WQ/kernel/power/process.c       2007-02-19 01:04:26.000000000 +0300
> > @@ -46,8 +46,10 @@ void refrigerator(void)
> >     recalc_sigpending(); /* We sent fake signal, clean it up */
> >     spin_unlock_irq(&current->sighand->siglock);
> >  
> > -           current->state = TASK_UNINTERRUPTIBLE;
> > +           set_current_state(TASK_UNINTERRUPTIBLE);
> 
> 
> Looks okay to me... but this one liner would be exactly as effective,
> right?

I think no, with this one liner we have

        while (frozen(current)) {
                // ------ WINDOW ------------
                set_current_state(TASK_UNINTERRUPTIBLE);
                schedule();
        }

What if thaw_process() happens in the window above?

We need the barrier exactly because LOAD (check condition) should not
come before STORE (set task->state).

Oleg.

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