linux-kernel - Re: [PATCH 1/8] pci: Make sriov work with hotplug removal

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Message-ID: <4EA6ACBA.20200@jp.fujitsu.com>
Date:	Tue, 25 Oct 2011 21:34:02 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Yinghai Lu <yinghai.lu@...cle.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/8] pci: Make sriov work with hotplug removal

(2011/10/19 2:02), Yinghai Lu wrote:
> On 10/18/2011 09:49 AM, Bjorn Helgaas wrote:
>> On Mon, Oct 17, 2011 at 4:24 PM, Yinghai Lu<yinghai.lu@...cle.com> wrote:
>>> On 10/17/2011 03:12 PM, Bjorn Helgaas wrote:
>>>>
>>>> Maybe this is the best we can do, but it still doesn't seem ideal, and
>>>> it's certainly not obvious when reading the code. It doesn't seem
>>>> right for the driver ->remove() method to be calling
>>>> pci_destroy_dev(). Won't the core data structures be corrupted if a
>>>> defective driver doesn't call pci_disable_sriov()? Seems like we
>>>> could end up with a device that's been physically removed, but still
>>>> has pci_dev structs hanging around.
>>>
>>> i did add some print out in
>>> pci_stop_bus_device
>>> when stop PF, that function is called for those VFs.
>>>
>>> also driver have to call pci_disable_sriov() and that is current design.
>>
>> Yep. But I don't have to like the current design :) It doesn't seem
>> as robust as it could be.
>>
>> It took me a long time to puzzle out what was happening here. Here's
>> some possible changelog text that would have saved me a lot of time:
>>
>> The PCI hot-remove path calls pci_stop_bus_devices() via
>> pci_remove_bus_device().
>>
>> pci_stop_bus_devices() traverses the bus->devices list (point A below),
>> stopping each device in turn, which calls the driver remove() method. When
>> the device is an SR-IOV PF, the driver calls pci_disable_sriov(), which
>> also uses pci_remove_bus_device() to remove the VF devices from the
>> bus->devices list (point B).
>>
>> pci_remove_bus_device
>> pci_stop_bus_device
>> pci_stop_bus_devices(subordinate)
>> list_for_each(bus->devices)<-- A
>> pci_stop_bus_device(PF)
>> ...
>> driver->remove
>> pci_disable_sriov
>> ...
>> pci_remove_bus_device(VF)
>> <remove from bus_list> <-- B
>>
>> At B, we're changing the same list we're iterating through at A, so when
>> the driver remove() method returns, the pci_stop_bus_devices() iterator has
>> a pointer to a list entry that has already been freed.
>>
>> This patch avoids the problem by building a separate list of all PFs on
>> the bus and traversing that at A instead of the bus->devices list.
> 
> yes.

I have one question.

I think pci_stop_bus_devices() is called only when bridge device is removed.
Are you trying to hot-remove the bridge device that has SR-IOV capable
devices on the subordinate bus?

Regards,
Kenji Kaneshige
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