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

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Message-ID: <20220826211401.GA2959769@bhelgaas>
Date:   Fri, 26 Aug 2022 16:14:01 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH -next 1/3] PCI: fix double put_device() in error case in
 pci_create_root_bus()

[+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.

> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
>  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.

>  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
>