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

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Date:   Thu, 3 Sep 2020 08:35:33 -0600
From:   Rob Herring <robh@...nel.org>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Samuel Dionne-Riel <samuel@...nne-riel.com>,
        Marc Zyngier <maz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        devicetree@...r.kernel.org, Frank Rowand <frowand.list@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Boot failure on gru-scarlet-inx with 5.9-rc2

On Thu, Sep 3, 2020 at 3:19 AM Lorenzo Pieralisi
<lorenzo.pieralisi@....com> wrote:
>
> On Wed, Sep 02, 2020 at 11:47:56PM -0400, Samuel Dionne-Riel wrote:
> > On Wed, 2 Sep 2020 17:01:19 +0100
> > Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:
> >
> > > On Tue, Sep 01, 2020 at 02:33:56PM -0400, Samuel Dionne-Riel wrote:
> > >
> > > Please print a pointer as a pointer and print both bus and
> > > bus->parent.
> >
> > Hopefully pointer as a pointer is %px. Not sure what else, if that's
> > wrong please tell.
> >
> > ---
> > @@ -79,6 +79,8 @@ static int rockchip_pcie_valid_device(struct rockchip_pcie *rockchip,
> >          * do not read more than one device on the bus directly attached
> >          * to RC's downstream side.
> >          */
> > +       printk("[!!] // bus (%px) bus->parent (%px)\n", bus, bus->parent);
> > +       printk("[!!] bus->primary (%d) == rockchip->root_bus_nr (%d) && dev (%d) > 0\n", bus->primary, rockchip->root_bus_nr, dev);
> >         if (bus->primary == rockchip->root_bus_nr && dev > 0)
> >                 return 0;
> >
> > --
> >
> > Again, two values, verified with a bit of set and `sort -u`.
> >
> > [    1.691266] [!!] // bus (ffff0000ef9ab800) bus->parent (0000000000000000)
> > [    1.691271] [!!] bus->primary (0) == rockchip->root_bus_nr (0) && dev (0) > 0
> >
> > and
> >
> > [    1.697156] [!!] // bus (ffff0000ef9ac000) bus->parent (ffff0000ef9ab800)
> > [    1.697160] [!!] bus->primary (0) == rockchip->root_bus_nr (0) && dev (0) > 0
> >
> > First instance of each shown here. Last time I don't think it was.
>
> 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)
+               /*
+                * do not read more than one device on the bus directly attached
+                * to RC's downstream side.
+                */
                return 0;

        return 1;


>
> -- >8 --
> diff --git a/drivers/pci/controller/pcie-rockchip-host.c b/drivers/pci/controller/pcie-rockchip-host.c
> index 0bb2fb3e8a0b..72beda87b47f 100644
> --- a/drivers/pci/controller/pcie-rockchip-host.c
> +++ b/drivers/pci/controller/pcie-rockchip-host.c
> @@ -79,7 +79,7 @@ static int rockchip_pcie_valid_device(struct rockchip_pcie *rockchip,
>          * 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 (bus->parent && pci_is_root_bus(bus->parent) && dev > 0)
>                 return 0;
>
>         return 1;