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Date: Thu, 25 Jun 2009 10:41:09 -0600
From: Alex Chiang <achiang@hp.com>
To: Troy Moure <twmoure@szypr.net>
Cc: Alessandro Suardi <alessandro.suardi@gmail.com>,
       Bjorn Helgaas <bjorn.helgaas@hp.com>, linux-kernel@vger.kernel.org
Subject: Re: [2.6.31-rc1] oops in acpi_get_pci_dev
Message-ID: <20090625164109.GK17633@ldl.fc.hp.com>
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* Troy Moure <twmoure@szypr.net>:
> Alessandro Suardi wrote:
> > On boot:
> ...
> > kernel: BUG: unable to handle kernel NULL pointer dereference at
> > 0000000000000018
> > kernel: IP: [<ffffffff8121b556>] acpi_get_pci_dev+0x113/0x17
> ...
> > Dell Latitude E6400 x86_64 SMP with Fedora 11 userspace.
> 
> > Box continues working after Oops, but locks up when exiting X session.
> 
> > 2.6.30-git22 works fine (probably because acpi_get_pci_dev is
> > introduced in -rc1)

Sorry about this panic. I was nervous about touching the ACPI
backlight stuff, and with good reason, it seems.

> I've encountered what seems to be the same issue (a NULL pointer 
> dereference in acpi_get_pci_dev()).  In my case, it caused a kernel panic 
> during boot (so I don't have any text logs to attach).
> 
> In my case, pci_get_slot() is returning a NULL pointer that  
> acpi_get_pci_dev() doesn't check for.  The following patch fixes things 
> for me.  Does it work for you, Alessandro?
> 
> (I don't know if it's the "right" fix or not, not being familiar with the 
> system.  If it is, I can send it in as a proper patch.)

Let me have a think about this.

Thanks.

/ac

> 
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 8a5bf3b..55b5b90 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -395,7 +395,7 @@ struct pci_dev *acpi_get_pci_dev(acpi_handle handle)
>  		fn  = adr & 0xffff;
>  
>  		pdev = pci_get_slot(pbus, PCI_DEVFN(dev, fn));
> -		if (hnd == handle)
> +		if (!pdev || hnd == handle)
>  			break;
>  
>  		pbus = pdev->subordinate;
>