linux-kernel - Re: Boot failure on gru-scarlet-inx with 5.9-rc2

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Date:   Thu, 3 Sep 2020 15:21:40 -0400
From:   Samuel Dionne-Riel <samuel@...nne-riel.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Rob Herring <robh@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        devicetree@...r.kernel.org, Frank Rowand <frowand.list@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: Boot failure on gru-scarlet-inx with 5.9-rc2

On Thu, 03 Sep 2020 16:59:30 +0100
Marc Zyngier <maz@...nel.org> wrote:

> On 2020-09-03 15:35, Rob Herring wrote:
> > On Thu, Sep 3, 2020 at 3:19 AM Lorenzo Pieralisi
> > <lorenzo.pieralisi@....com> wrote:  
> >> 
> >> Ok I think I understand what the problem is.
> >> 
> >> Can you give this patch a shot please ? I think we are
> >> dereferencing a NULL pointer if bus is the root bus and dev == 0,
> >> we can rewrite the check if this patch fixes the issue.  
> > 
> > Indeed. I checked all the other cases of
> > pci_is_root_bus(bus->parent) and they should be fine because they
> > are only reached if !root_bus.
> > 
> > I would restructure the check like this instead:
> > 
> > diff --git a/drivers/pci/controller/pcie-rockchip-host.c
> > b/drivers/pci/controller/pcie-rockchip-host.c
> > index 0bb2fb3e8a0b..9b485bea8b92 100644
> > --- a/drivers/pci/controller/pcie-rockchip-host.c
> > +++ b/drivers/pci/controller/pcie-rockchip-host.c
> > @@ -72,14 +72,14 @@ static int rockchip_pcie_valid_device(struct
> > rockchip_pcie *rockchip,
> >                                       struct pci_bus *bus, int dev)
> >  {
> >         /* access only one slot on each root port */
> > -       if (pci_is_root_bus(bus) && dev > 0)
> > -               return 0;
> > -
> > -       /*
> > -        * do not read more than one device on the bus directly 
> > attached
> > -        * to RC's downstream side.
> > -        */
> > -       if (pci_is_root_bus(bus->parent) && dev > 0)
> > +       if (pci_is_root_bus(bus))
> > +               if (dev > 0)
> > +                       return 0;
> > +       else if (pci_is_root_bus(bus->parent) && dev > 0)  
> 
> Careful here, this else is relative to the *closest* if,
> and not what the indentation suggests...
> 
> > +               /*
> > +                * do not read more than one device on the bus
> > directly attached
> > +                * to RC's downstream side.
> > +                */
> >                 return 0;
> > 
> >         return 1;  
> 
> 
>          M.

Both patches work fine. They both allow the device to boot and Wi-Fi to
work as expected.

I will echo Marc's concerns over the indentation. I am only casually
acquainted with C and this indentation would bring to wrong conclusions
if it hadn't been pointed out to me.

Cc me on an eventual patch, FWIW I can give it a final test just in
case.

Thanks again,

-- 
Samuel Dionne-Riel