Re: [PATCH v3 3/3] uio: fix crash after the device is unregistered

[Xiubo Li]

On 2018/7/10 1:06, Mike Christie wrote:
> On 07/06/2018 08:28 PM, Xiubo Li wrote:
> > On 2018/7/7 2:23, Mike Christie wrote:
> > > On 07/05/2018 09:57 PM, xiubli@xxxxxxxxxx wrote:
> > > >    static irqreturn_t uio_interrupt(int irq, void *dev_id)
> > > >    {
> > > >        struct uio_device *idev = (struct uio_device *)dev_id;
> > > > -    irqreturn_t ret = idev->info->handler(irq, idev->info);
> > > > +    irqreturn_t ret;
> > > > +
> > > > +    mutex_lock(&idev->info_lock);
> > > > +    if (!idev->info) {
> > > > +        ret = IRQ_NONE;
> > > > +        goto out;
> > > > +    }
> > > >    +    ret = idev->info->handler(irq, idev->info);
> > > >        if (ret == IRQ_HANDLED)
> > > >            uio_event_notify(idev->info);
> > > >    +out:
> > > > +    mutex_unlock(&idev->info_lock);
> > > >        return ret;
> > > >    }
> > > Do you need the interrupt related changes in this patch and the first
> > > one?
> > Actually, the NULL checking is not a must, we can remove this. But the
> > lock/unlock is needed.
> > >    When we do uio_unregister_device -> free_irq does free_irq return
> > > when there are no longer running interrupt handlers that we requested?
> > >
> > > If that is not the case then I think we can hit a similar bug. We do:
> > >
> > > __uio_register_device -> device_register -> device's refcount goes to
> > > zero so we do -> uio_device_release -> kfree(idev)
> > >
> > > and if it is possible the interrupt handler could still run after
> > > free_irq then we would end up doing:
> > >
> > > uio_interrupt -> mutex_lock(&idev->info_lock) -> idev access freed
> > > memory.
> > I think this shouldn't happen. Because the free_irq function does not
> > return until any executing interrupts for this IRQ have completed.
> If free_irq returns after executing interrupts and does not allow new
> executions what is the lock protecting in uio_interrupt?
I meant idev->info->handler(irq, idev->info), it may should be protected 
by the related lock in each driver.

Thanksï