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 21:38:02 +0800
From:   Ding Tianhong <dingtianhong@...wei.com>
To:     Thierry Reding <thierry.reding@...il.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 2017/8/17 21:30, Thierry Reding wrote:
> 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.
> 

Ok, NO problem.:)

> Thierry
>