Message-ID: <865795326.20150526095335@eikelenboom.it>
Date:	Tue, 26 May 2015 09:53:35 +0200
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	david.vrabel@...rix.com, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI / ACPI: Do not set ACPI companions for host bridges with parents


Tuesday, May 26, 2015, 4:17:05 AM, you wrote:

> On Tuesday, May 26, 2015 03:08:17 AM Rafael J. Wysocki wrote:
>> On Tuesday, May 26, 2015 01:42:16 AM Rafael J. Wysocki wrote:
>> > On Tuesday, May 26, 2015 01:22:12 AM Rafael J. Wysocki wrote:
>> > > On Friday, May 22, 2015 09:53:37 PM Boris Ostrovsky wrote:
>> > > > On 05/22/2015 04:11 AM, Sander Eikelenboom wrote:
>> > > > > Hello Sander,
>> > > > >
>> > 
>> > [cut]
>> > 
>> > > > (+Rafael again)
>> > > > 
>> > > > So the immediate cause of those errors is that pdev->evtchn is 0. 
>> > > > Backend is not notified and things not go well then.
>> > > > 
>> > > > And it is indeed caused by 97badf873ab60e841243b66133ff9eff2a46ef29:
>> > > > 
>> > > > We allocate pcifront_sd in pcifront_scan_root() and then pass it to 
>> > > > pci_scan_bus_parented() as sysdata. Eventually this sysdata is used in 
>> > > > pcibios_root_bridge_prepare() as pci_sysdata. It is dereferenced as 
>> > > > pci_sysdata->companion (which I believe is aliased to pcifront_sd->pdev)
>> > 
>> > Well, there is an int node field between them, so I'm not sure.
>> > 
>> > > > and then set_primary_fwnode() writes it, thus corrupting 
>> > > > pcifront_sd->pdev (and I think this is what sets evtchn to zero).
>> > 
>> > So the corruption happens when set_primary_fwnode() writes NULL to the
>> > 'secondary' field of object pointed to by 'fwnode'.
>> > 
>> > This isn't strictly necessary and we might avoid the crash by only
>> > writing to fwnode->secondary if fn is not NULL.
>> > 
>> > So, Sander please test the patch below too if possible.
>> > 
>> > Of course, that doesn't solve a problem of passing an incorrect pointer
>> > to ACPI_COMPANION_SET() in pcibios_root_bridge_prepare().
>> 
>> And here's one more thing to test.

> And the below is how I'd fix it, so you can simply test this patch and skip the
> previous ones.

Hi Rafael,

Just tested it, works for me, thanks !

--
Sander


> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Subject: PCI / ACPI: Do not set ACPI companions for host bridges with parents

> Commit 97badf873ab6 (device property: Make it possible to use
> secondary firmware nodes) uncovered a bug in the x86 (and ia64) PCI
> host bridge initialization code that assumes bridge->bus->sysdata
> to always point to a struct pci_sysdata object which need not be
> the case (in particular, the Xen PCI frontend driver sets it to point
> to a different data type).  If it is not the case, an incorrect
> pointer (or a piece of data that is not a pointer at all) will be
> passed to ACPI_COMPANION_SET() and that may cause interesting
> breakage to happen going forward.

> To work around this problem use the observation that the ACPI
> host bridge initialization always passes NULL as parent to
> pci_create_root_bus(), so if pcibios_root_bridge_prepare() sees
> a non-NULL parent of the bridge, it should not attempt to set
> an ACPI companion for it, because that means that
> pci_create_root_bus() has been called by someone else.

> Reported-by: Sander Eikelenboom <linux@...elenboom.it>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  arch/ia64/pci/pci.c |   13 ++++++++++---
>  arch/x86/pci/acpi.c |   13 ++++++++++---
>  2 files changed, 20 insertions(+), 6 deletions(-)

> Index: linux-pm/arch/x86/pci/acpi.c
> ===================================================================
> --- linux-pm.orig/arch/x86/pci/acpi.c
> +++ linux-pm/arch/x86/pci/acpi.c
> @@ -482,9 +482,16 @@ struct pci_bus *pci_acpi_scan_root(struc
>  
>  int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
>  {
> -       struct pci_sysdata *sd = bridge->bus->sysdata;
> -
> -       ACPI_COMPANION_SET(&bridge->dev, sd->companion);
> +       /*
> +        * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
> +        * here, pci_create_root_bus() has been called by someone else and
> +        * sysdata is likely to be different from what we expect.  Let it go in
> +        * that case.
> +        */
> +       if (!bridge->dev.parent) {
> +               struct pci_sysdata *sd = bridge->bus->sysdata;
> +               ACPI_COMPANION_SET(&bridge->dev, sd->companion);
> +       }
>         return 0;
>  }
>  
> Index: linux-pm/arch/ia64/pci/pci.c
> ===================================================================
> --- linux-pm.orig/arch/ia64/pci/pci.c
> +++ linux-pm/arch/ia64/pci/pci.c
> @@ -478,9 +478,16 @@ struct pci_bus *pci_acpi_scan_root(struc
>  
>  int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
>  {
> -       struct pci_controller *controller = bridge->bus->sysdata;
> -
> -       ACPI_COMPANION_SET(&bridge->dev, controller->companion);
> +       /*
> +        * We pass NULL as parent to pci_create_root_bus(), so if it is not NULL
> +        * here, pci_create_root_bus() has been called by someone else and
> +        * sysdata is likely to be different from what we expect.  Let it go in
> +        * that case.
> +        */
> +       if (!bridge->dev.parent) {
> +               struct pci_controller *controller = bridge->bus->sysdata;
> +               ACPI_COMPANION_SET(&bridge->dev, controller->companion);
> +       }
>         return 0;
>  }
>  



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