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SubjectRe: [PATCH v3 3/3] uio: fix crash after the device is unregistered
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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@redhat.com 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.

Thanks,

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