On Fri, 22 Jun 2018, Lukas Wunner wrote:
> 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.
Missed that. Fair enough.
Thanks,
tglx
