linux-kernel - Re: [PATCH] PCI: fix reference leak in pci_alloc_child

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Message-ID: <479bf618-187e-14f0-5319-c41f8b80faeb@linux.intel.com>
Date: Wed, 18 Dec 2024 17:12:57 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Ma Ke <make_ruc2021@....com>, Lukas Wunner <lukas@...ner.de>, 
    bhelgaas@...gle.com
cc: rafael.j.wysocki@...el.com, yinghai@...nel.org, linux-pci@...r.kernel.org, 
    LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] PCI: fix reference leak in pci_alloc_child_bus()

On Tue, 17 Dec 2024, Ma Ke wrote:

> When device_register(&child->dev) failed, calling put_device() to
> explicitly release child->dev. Otherwise, it could cause double free
> problem.
> 
> Found by code review.
> 
> Cc: stable@...r.kernel.org
> Fixes: 4f535093cf8f ("PCI: Put pci_dev in device tree as early as possible")
> Signed-off-by: Ma Ke <make_ruc2021@....com>
> ---
>  drivers/pci/probe.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 2e81ab0f5a25..d3146c588d7f 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1174,7 +1174,10 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
>  add_dev:
>  	pci_set_bus_msi_domain(child);
>  	ret = device_register(&child->dev);
> -	WARN_ON(ret < 0);
> +	if (ret) {
> +		WARN_ON(ret < 0);

The usual way is:

	if (WARN_ON(ret < 0))

> +		put_device(&child->dev);
> +	}
>  
>  	pcibios_add_bus(child);

But more serious problem here is that should this code even proceed as if 
nothing happened when an error occurs? pci_register_host_bridge() does 
proper rollback when device_register() fails but this function doesn't.

Into the same vein, is using WARN_ON() even correct here? Why should this 
print a stacktrace if device_register() fails instead of simply printing 
and error?

-- 
 i.