Re: [PATCH -next 1/3] PCI: fix double put_device() in error case in pci_create_root_bus()

[Yang Yingliang]

Hi,

On 2022/8/27 5:14, Bjorn Helgaas wrote:
> [+cc Rob]
>
> On Thu, Aug 25, 2022 at 08:27:51PM +0800, Yang Yingliang wrote:
> > If device_add() fails in pci_register_host_bridge(), the brigde device will
> > be put once, and it will be put again in error path of pci_create_root_bus().
> > Move the put_device() from pci_create_root_bus() to pci_register_host_bridge()
> > to fix this problem. And use device_unregister() instead of del_device() and
> > put_device().
> s/brigde/bridge/
>
> > Fixes: 9885440b16b8 ("PCI: Fix pci_host_bridge struct device release/free handling")
> If you're fixing a commit from somebody else, please always cc: the
> author because the author can help review the change.
OK.
> > Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> > ---
> >   drivers/pci/probe.c | 8 ++------
> >   1 file changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index c5286b027f00..e500eb9d6468 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -1027,7 +1027,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
> >   
> >   unregister:
> >   	put_device(&bridge->dev);
> > -	device_del(&bridge->dev);
> > +	device_unregister(&bridge->dev);
> I don't understand this part.  device_unregister() looks like this:
>
>    void device_unregister(struct device *dev)
>    {
>      device_del(dev);
>      put_device(dev);
>    }
>
> So this calls put_device(&bridge->dev) twice, doesn't it?
>
> The "unregister" label looks poorly named.  We only get there if
> device_register() *failed*.  We shouldn't need to unregister anything
> in that case.
If it goes to the 'unregister' label, the bridge->dev has been register 
sucessfully (device_initialize() called from pci_alloc_host_bridge()
and device_add() called from pci_register_host_bridge()), so it need be 
unregister, and another put_device() is for decreasing
refcount of 'bus->bridge'.

Thanks,
Yang
> >   free:
> >   	kfree(bus);
> > @@ -3037,13 +3037,9 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
> >   
> >   	error = pci_register_host_bridge(bridge);
> >   	if (error < 0)
> > -		goto err_out;
> > +		return NULL;
> >   
> >   	return bridge->bus;
> > -
> > -err_out:
> > -	put_device(&bridge->dev);
> > -	return NULL;
> This part looks right to me.  The get_device() is in
> pci_register_host_bridge(), and if pci_register_host_bridge() returns
> failure, I think it should first do the corresponding put_device().
>
> >   }
> >   EXPORT_SYMBOL_GPL(pci_create_root_bus);
> >   
> > --
> > 2.25.1
> .