netdev - Re: [PATCH net RESEND] PCI: fix oops when try to find Root Port for a PCI device

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Message-ID: <87fucqsrol.fsf@concordia.ellerman.id.au>
Date:   Thu, 17 Aug 2017 15:12:58 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Thierry Reding <thierry.reding@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Ding Tianhong <dingtianhong@...wei.com>, mark.rutland@....com,
        gabriele.paoloni@...wei.com, asit.k.mallick@...el.com,
        catalin.marinas@....com, will.deacon@....com, linuxarm@...wei.com,
        alexander.duyck@...il.com, ashok.raj@...el.com,
        eric.dumazet@...il.com, jeffrey.t.kirsher@...el.com,
        linux-pci@...r.kernel.org, ganeshgr@...lsio.com, Bob.Shaw@....com,
        leedom@...lsio.com, patrick.j.cramer@...el.com,
        bhelgaas@...gle.com, werner@...lsio.com,
        linux-arm-kernel@...ts.infradead.org, amira@...lanox.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        David.Laight@...lab.com, Suravee.Suthikulpanit@....com,
        robin.murphy@....com, davem@...emloft.net, l.stach@...gutronix.de
Subject: Re: [PATCH net RESEND] PCI: fix oops when try to find Root Port for a PCI device

Thierry Reding <thierry.reding@...il.com> writes:
...
>
> In case of Tegra, dev actually points to the root port. Now if I read
> the above code correctly, highest_pcie_bridge will still be NULL in that
> case, which in turn will return NULL from pci_find_pcie_root_port(). But
> shouldn't it really return dev?
>
> The patch that I used to fix the issue is this:
>
> --->8---
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 2c712dcfd37d..dd56c1c05614 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -514,7 +514,7 @@ EXPORT_SYMBOL(pci_find_resource);
>   */
>  struct pci_dev *pci_find_pcie_root_port(struct pci_dev *dev)
>  {
> -       struct pci_dev *bridge, *highest_pcie_bridge = NULL;
> +       struct pci_dev *bridge, *highest_pcie_bridge = dev;
>  
>         bridge = pci_upstream_bridge(dev);
>         while (bridge && pci_is_pcie(bridge)) {
> --->8---
>
> That works correctly if this function ends up being called on the PCIe
> root port, though perhaps that's not what this function is supposed to
> do. It's somewhat unclear from the kerneldoc what the function should
> be doing when called on a root port device itself.

That also works for me on powerpc (oops reported up thread).

cheers