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

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Message-ID: <4E9DB11A.7030505@oracle.com>
Date:	Tue, 18 Oct 2011 10:02:18 -0700
From:	Yinghai Lu <yinghai.lu@...cle.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	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

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.
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