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 15:30:12 +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 08:40:16PM +0800, Ding Tianhong wrote:
> 
> 
> On 2017/8/17 18:51, Thierry Reding wrote:
> > 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.
> > 
> 
> Hi Thierry:
> 
> The patch ("PCI: fix oops when try to find Root Port for a PCI device")
> has been merge to the linus mainline tree before you found this deficiencies....

I understand that. I'm just saying that there's no point keeping that
change around because it no longer makes sense after we initialize the
highest_pcie_bridge variable to dev.

Thierry

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