Re: [PATCH/RFC 0/5] Fix the sh_eth race between open and MDIO bus registration

[Ben Dooks <ben.dooks@codethink.co.uk>]

On 19/03/14 16:06, Laurent Pinchart wrote:
> Hi Geert,
>
> On Wednesday 19 March 2014 14:35:59 Geert Uytterhoeven wrote:
>> On Wed, Mar 19, 2014 at 11:07 AM, Laurent Pinchart wrote:
>>> On Wednesday 19 March 2014 10:14:53 Ben Dooks wrote:
>>>> On 19/03/14 08:41, Geert Uytterhoeven wrote:
>>>>> On Wed, Mar 19, 2014 at 12:25 AM, Laurent Pinchart wrote:
>>>>>> Laurent Pinchart (5):
>>>>>>     sh_eth: Use the platform device for memory allocation
>>>>>>     sh_eth: Use the platform device as the MDIO bus parent
>>>>>>     sh_eth: Simplify MDIO bus initialization and release
>>>>>>     sh_eth: Register MDIO bus before registering the network device
>>>>>>     sh_eth: Remove goto statements that jump straight to a return
>>>>>
>>>>> Thanks, the changes look fine to me, so
>>>>
>>>> I think the only issue I have is the re-parent of the MDIO device.
>>>>
>>>> My view also is that the probe should explicitly get a reference if it is
>>>> going to be created sub-devices.
>>>
>>> I'm not sure to follow you, could you please elaborate on that ? What
>>> should take a reference on what ?
>>
>> I think he means a runtime pm reference, and he is right.
>>
>> I gave your series a try on Koelsch. Now the clock is:
>>    1. enabled in sh_eth_drv_probe(),
>>    2. disabled from the worker thread,
>>    3. enabled and disabled in sh_eth_get_stats(),
>>    4. enabled in sh_eth_open() for nfsroot,
>>    5. disabled in sh_eth_close() on shutdown,
>>    6. enabled and disabled in sh_eth_get_stats().
>>
>> I wondered whether 2 could happen too soon, so I added msleep(2000) to
>> sh_eth_drv_probe(), just after the call to pm_runtime_resume(). Then it
>> fails to obtain the MAC address:
>>
>> sh-eth ee700000.ethernet: no valid MAC address supplied, using a random one.
>>
>> Due to 4, the network hardware works, and it manages to receive an IP
>> address from my DHCP server. But as the MAC address is wrong, the IP address
>> is also wrong, and it hangs when trying to mount NFS.
>>
>> Applying Ben's "PATCH] sh_eth: ensure pm_runtime cannot suspend the device
>> during init" fixes this.
>
> I've investigated the issue. The pm_runtime_resume() call from the sh_eth
> probe function ends up calling rpm_resume() synchronously. The function
> resumes the device, and right before returning calls rpm_idle(dev, RPM_ASYNC).
> This queues a RPM_REQ_IDLE request, resulting in the device being suspended
> the next time the work queue is run.
>
> pm_runtime_resume() seem to be unsafe at probe time if the PM workqueue can
> run before the probe function is done with the device, which means pretty much
> everywhere as probe() usually calls functions that can sleep.
>
> I thus agree that a pm_runtime_get_sync() call is needed. The
> pm_runtime_put_sync() call at the end of the probe function could be replaced
> by a pm_runtime_put() call though. The PM runtime documentation should also be
> updated.

Thanks, that validates what I saw but did not get time to fully
trace.

I agree that pm_runtime_put() is probably a better option as we do
not need to ensure that the device is shut down immediately. I will
re-do the patch and submit it tonight.

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius