Re: [RFC PATCH v1 00/22] introduce PCI bus lock to serialize PCIhotplug operations

[Jiang Liu]

On 08/08/2012 02:11 AM, Don Dutile wrote:
> On 08/07/2012 12:10 PM, Jiang Liu wrote:
>> From: Jiang Liu<liuj97@xxxxxxxxx>
>>
>> This is the second take to resolve race conditions when hot-plugging PCI
>> devices/host bridges. Instead of using a globla lock to serialize all hotplug
>> operations as in previous version, now we introduce a state machine and bit
>> lock mechanism for PCI buses to serialize hotplug operations. For discussions
>> related to previous version, please refer to:
>> http://comments.gmane.org/gmane.linux.kernel.pci/15007
>>
>> This patch-set is still in early stages, so sending it out just requesting
>> for comments. Any comments are welcomed, especially about whether it's the
>> right/suitable way to solve these race condition issues.
>>
>> patch 1-5:
>>     Preparing for coming PCI bus lock
>> patch 6-7:
>>     Core of the new PCI bus lock mechanism.
>> patch 8-13:
>>     Enhance PCI core to support PCI bus lock mechanism.
>> patch 14-18:
>>     Enhance several PCI hotplug drivers to use PCI bus lock to serialize
>>     hotplug operations.
>> patch 19-20:
>>     Enable PCI bus lock mechanism for x86 and IA64, still need to enable
>>     PCI bus lock for other archs.
>> patch 21-22:
>>     Cleanups for unsed code.
>>
>> There are multiple methods to trigger PCI hotplug requests/operations
>> concurrently, such as:
>> 1. Sysfs interfaces exported by the PCI core subsystem
>>     /sys/devices/pcissss:bb/ssss:bb:dd.f/.../remove
>>     /sys/devices/pcissss:bb/ssss:bb:dd.f/.../rescan
>>     /sys/devices/pcissss:bb/ssss:bb:dd.f/.../pci_bus/ssss:bb/rescan
>>     /sys/bus/pci/rescan
>> 2. Sysfs interfaces exported by the PCI hotplug subsystem
>>     /sys/bus/pci/slots/xx/power
>> 3. PCI hotplug events triggered by PCI Hotplug Controllers
>> 4. ACPI hotplug events for PCI host bridges
>> 5. Driver binding/unbinding events
>>     binding/unbinding pci drivers with SR-IOV support
>>
> 6. PCI reset
>    --> a PCIe device-level reset is done by KVM when it assigns a device
>        to a guest.  a PCI config-save before reset, and PCI config-restore after reset
>        is done in this case.
>    --> VF devices are interesting, since they are reset, then bound to
>        pci-stub driver.  when more than 1 VF is enabled in a PF,
>        and several device-assignments are done simultaneously, you
>        get a storm of reset (save/restore pci cfg space), and pci-stub binding
>        (pci cfg read for resource allocation/deallocation), and depending on
>        the hw design: an AER caused by the FLR reset -- not suppose to, but
>        hw has bugs too! ;-)
>    PCI locking is 'challenged' in the above scenario.
> 
>   So, I ask: have you tried your patch set doing something like:
>     a) modprobe an SRIOV device with > 1 vf enabled
>   you may also have to do:
>     b) while assigning another SRIOV device's VF to another KVM guest
> 
> Unfortunately, the PCI cfg-space locking, esp. on x86 (ok, I'll say it:
> damn, mutually exclusive, IO-port-based cfg registers), doesn't lend itself
> to this multi-task, dynamic PCI scenario.
> Much less complicated on linearly-mapped, PCI-mmconf-only accesses.
> 
> - Don
Hi Don,
	Thanks for your comments. Haven't done such tests for SR-IOV yet. We will
try to find some NICs with SR-IOV capability for testing and will send the result
to you once done.
	Regards!
	Gerry

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