linux-kernel - Re: [PATCH net] PCI: fix the return value for the pci_find_pcie_root

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Date:   Thu, 17 Aug 2017 12:51:56 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Ding Tianhong <dingtianhong@...wei.com>
Cc:     leedom@...lsio.com, ashok.raj@...el.com, bhelgaas@...gle.com,
        helgaas@...nel.org, werner@...lsio.com, ganeshgr@...lsio.com,
        asit.k.mallick@...el.com, patrick.j.cramer@...el.com,
        Suravee.Suthikulpanit@....com, Bob.Shaw@....com,
        l.stach@...gutronix.de, amira@...lanox.com,
        gabriele.paoloni@...wei.com, David.Laight@...lab.com,
        jeffrey.t.kirsher@...el.com, catalin.marinas@....com,
        will.deacon@....com, mark.rutland@....com, robin.murphy@....com,
        davem@...emloft.net, alexander.duyck@...il.com,
        eric.dumazet@...il.com, linux-arm-kernel@...ts.infradead.org,
        netdev@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com
Subject: Re: [PATCH net] PCI: fix the return value for the
 pci_find_pcie_root_port()

On Thu, Aug 17, 2017 at 10:25:30AM +0800, Ding Tianhong wrote:
> The pci_find_pcie_root_port() would return NULL if the given
> dev is already a Root Port, it looks like unfriendly to the
> PCIe Root Port device, Thierry and Bjorn suggest to let this
> function return the given dev under this circumstances.
> 
> Fixes: 0e405232871d6 ("PCI: fix oops when try to find Root Port for a PCI device")
> Suggested-by: Thierry Reding <thierry.reding@...il.com>
> Suggested-by: Bjorn Helgaas <helgaas@...nel.org>
> Signed-off-by: Thierry Reding <thierry.reding@...il.com>
> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
> ---
>  drivers/pci/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7e2022f..352bb53 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -514,7 +514,7 @@ struct resource *pci_find_resource(struct pci_dev *dev, struct resource *res)
>   */
>  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)) {

I think this should actually be this change on top of a revert of commit
0e405232871d6 ("PCI: fix oops when try to find Root Port for a PCI
device"). After the above change, the previous fix will have a redundant
check because highest_pcie_bridge will never be NULL.

Let me send out that version to clarify what I mean.

Thierry

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