Hi Michael,
>> >> Fix panic in virtio.c when CONFIG_DEBUG_SLAB is set.
>> >
>> > What's the root cause of the panic?
>>
>> I believe the cause of the panic is calling
>> ida_simple_remove(&virtio_index_ida, dev->index);
>> when the dev structure is "poisoned" after kfree.
>> It might be the "BUG_ON((int)id < 0)" that bites...
>>
>> >> Use device_del() and put_device() instead of
>> >> device_unregister(), and access device data before
>> >> calling put_device().
>>
>> > Why does this help? Does device_unregister free the
>> > device so dev->index access crashes?
>>
>> Yes, if device ref-count is one when calling unregister
>> the device is freed.
>
> Interesting. Where exactly?...
I was wrong here, the reason is not related to ref-count being
above one. The reason this issue do not show up in virtio_pci
is that the release function is a dummy:
[snip]
static void virtio_pci_release_dev(struct device *_d)
{
/*
* No need for a release method as we allocate/free
* all devices together with the pci devices.
* Provide an empty one to avoid getting a warning from core.
*/
}
The device structure uses a kref for reference counting the device.
In virtio_pci() the release function virtio_pci_release_dev()
will be called when the device is unregistered, but because the
release function is dummy, data isn't freed or reset at this point.
So for virtio devices created from virtio_pci my patch is not
currently needed.
However, empty release functions are not the preferred way, e.g look at
https://lkml.org/lkml/2012/4/3/301
[Greg K.H:]
> > > > +static void hsi_port_release(struct device *dev __maybe_unused)
> > > > +{
> > > > +}
> > >
> > > As per the documentation in the kernel tree, I get to mock you
> > > mercilessly for doing something as foolish as this. You are not smarter
> > > than the kernel and don't think that you got rid of the kernel warning
> > > properly by doing this. Do you think that I wrote that code for no good
> > > reason? The kernel was being nice and telling you what you did wrong,
> > > don't try to fake it out, it's smarter than you are here.
But remoteproc frees the device memory in the release function
rproc_vdev_release() and needs this patch.
Regards,
Sjur
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
