On Thu, Jun 21, 2018 at 10:21:44PM +0200, Thomas Gleixner wrote:
> On Thu, 24 May 2018, Lukas Wunner wrote:
> > static int irq_wait_for_interrupt(struct irqaction *action)
> > {
> > - set_current_state(TASK_INTERRUPTIBLE);
> > + for (;;) {
> > + set_current_state(TASK_INTERRUPTIBLE);
> >
> > - while (!kthread_should_stop()) {
> > + if (kthread_should_stop()) {
> > + /* may need to run one last time. */
> > + if (test_and_clear_bit(IRQTF_RUNTHREAD,
> > + &action->thread_flags)) {
> > + __set_current_state(TASK_RUNNING);
> > + return 0;
> > + }
> > + __set_current_state(TASK_RUNNING);
> > + return -1;
> > + }
> >
> > if (test_and_clear_bit(IRQTF_RUNTHREAD,
> > &action->thread_flags)) {
> > @@ -766,10 +776,7 @@ static int irq_wait_for_interrupt(struct irqaction *action)
> > return 0;
> > }
> > schedule();
> > - set_current_state(TASK_INTERRUPTIBLE);
> > }
> > - __set_current_state(TASK_RUNNING);
> > - return -1;
> > }
> >
> > /*
> > @@ -990,7 +997,7 @@ static int irq_thread(void *data)
> > /*
> > * This is the regular exit path. __free_irq() is stopping the
> > * thread via kthread_stop() after calling
> > - * synchronize_irq(). So neither IRQTF_RUNTHREAD nor the
> > + * synchronize_hardirq(). So neither IRQTF_RUNTHREAD nor the
> > * oneshot mask bit can be set. We cannot verify that as we
> > * cannot touch the oneshot mask at this point anymore as
> > * __setup_irq() might have given out currents thread_mask
> > @@ -1595,7 +1602,7 @@ static struct irqaction *__free_irq(struct irq_desc *desc, void *dev_id)
> > unregister_handler_proc(irq, action);
> >
> > /* Make sure it's not being used on another CPU: */
> > - synchronize_irq(irq);
> > + synchronize_hardirq(irq);
>
> So after that, action can be freed and when the thread above tries to
> access it. Nice Use After Free. That needs more thought.
No, after that, kthread_stop() is called which blocks until the IRQ
thread has completed. Only then is the action freed.
Thanks,
Lukas
