Subject: Re: [PATCH] Fix 3bc95598 'powerpc/PCI: Use list_for_each_entry() for bus traversal'

From: Benjamin Herrenschmidt <[email-masked]>
Date: Thu, 10 Apr 2014 17:54:23 +1000

On Thu, 2014-04-10 at 02:51 -0400, Mike Qiu wrote:
> Unable to handle kernel paging request for data at address 0x00000000
> Faulting instruction address: 0xc000000000041d78
> Oops: Kernel access of bad area, sig: 11 [#1]
> ...
> NIP [c000000000041d78] .sys_pciconfig_iobase+0x68/0x1f0
> LR [c000000000041e0c] .sys_pciconfig_iobase+0xfc/0x1f0
> Call Trace:
> [c0000003b4787db0] [c000000000041e0c] .sys_pciconfig_iobase+0xfc/0x1f0 (unreliable)
> [c0000003b4787e30] [c000000000009ed8] syscall_exit+0x0/0x98
> 
> This bug was introduced by commit 3bc955987fb377f3c95bc29deb498e96819b8451
> The root cause was the 'bus' has been set to null while try to access
> bus->next.

Good catch. Out of curiosity, what is using that syscall nowadays ? It's
been long buggy in all sort of ways and is pretty much deprecated...

Cheers,
Ben.

> Signed-off-by: Mike Qiu <[email-masked]>
> ---
>  arch/powerpc/kernel/pci_64.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/pci_64.c b/arch/powerpc/kernel/pci_64.c
> index 2a47790..7b6c1ae 100644
> --- a/arch/powerpc/kernel/pci_64.c
> +++ b/arch/powerpc/kernel/pci_64.c
> @@ -209,6 +209,7 @@ long sys_pciconfig_iobase(long which, unsigned long in_bus,
>  {
>  	struct pci_controller* hose;
>  	struct pci_bus *bus = NULL;
> +	struct pci_bus *tmp_bus = NULL;
>  	struct device_node *hose_node;
>  
>  	/* Argh ! Please forgive me for that hack, but that's the
> @@ -229,10 +230,12 @@ long sys_pciconfig_iobase(long which, unsigned long in_bus,
>  	 * used on pre-domains setup. We return the first match
>  	 */
>  
> -	list_for_each_entry(bus, &pci_root_buses, node) {
> -		if (in_bus >= bus->number && in_bus <= bus->busn_res.end)
> +	list_for_each_entry(tmp_bus, &pci_root_buses, node) {
> +		if (in_bus >= tmp_bus->number &&
> +		    in_bus <= tmp_bus->busn_res.end) {
> +			bus = tmp_bus;
>  			break;
> -		bus = NULL;
> +		}
>  	}
>  	if (bus == NULL || bus->dev.of_node == NULL)
>  		return -ENODEV;