On Mon, 2012-08-20 at 17:05 +0200, Oleg Nesterov wrote:
> On 08/20, Peter Zijlstra wrote:
> >
> > +static void __task_work_run(struct callback_head *tail)
> > {
> > - struct task_struct *task = current;
> > - struct callback_head *p, *q;
> > -
> > - while (1) {
> > - raw_spin_lock_irq(&task->pi_lock);
> > - p = task->task_works;
> > - task->task_works = NULL;
> > - raw_spin_unlock_irq(&task->pi_lock);
> > -
> > - if (unlikely(!p))
> > - return;
> > -
> > - q = p->next; /* head */
> > - p->next = NULL; /* cut it */
> > - while (q) {
> > - p = q->next;
> > - q->func(q);
> > - q = p;
> > + struct callback_head **head = ¤t->task_works;
> > +
> > + do {
> > + struct callback_head *work = xchg(head, NULL);
> > + while (work) {
> > + struct callback_head *next = ACCESS_ONCE(work->next);
> > +
> > + WARN_ON_ONCE(work == &dead);
> > +
> > + work->func(work);
> > + work = next;
> > }
> > - }
> > + } while (cmpxchg(head, NULL, tail) != NULL);
>
> Yes, we can add the explicit argument to __task_work_run(), but it can
> check PF_EXITING instead, this looks simpler to me.
I guess we could.. but I thought the explicit callback was simpler ;-)
> Note also your patch breaks fifo, but this is fixable.
Why do you care about the order? Iterating a single linked queue in fifo
seems more expensive than useful.
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