Re: [PATCH 2/3] spi: pxa2xx: Fix controller unregister order

[Tsuchiya Yuto <kitakar@xxxxxxxxx>]

On 5/27/20 9:27 PM, Andy Shevchenko wrote:
> On Wed, May 27, 2020 at 09:09:17PM +0900, Tsuchiya Yuto wrote:
>> I tried a kernel built with the prerequisite patch to this series + all
>> of patches in this series on top of v5.7-rc7 (with Arch Linux config
>> + olddefconfig).
>>
>> Current situations on 5.7-rc7 with Arch Linux config + olddefconfig
>> (without applying this series):
>> - I can reproduce the touch input crashing (surface3-spi) I mentioned
>>   in bugzilla [1] only after s2idle.
>> - all the other situations are the same as described in that bugzilla;
>>   I see NULL pointer dereference [2] after touch input crashing then try
>>   to unload only spi_pxa2xx_platform module.
>>
>> So, the steps to test that I did with this series applied are:
>> 1. go into s2idle then resume from s2idle
>> 2. make a touch input then surface3-spi reports that "SPI transfer
>>    timed out" repeatedly and no longer responds to any touch input
>> 3. try to unload only spi_pxa2xx_platform module and see if the NULL
>>    pointer dereference no longer occurs
>>
>> and I can confirm that I no longer see the NULL pointer dereference.
>> Thanks!
>
> Thank you very much for testing!
>
>> On 5/26/20 5:22 PM, Andy Shevchenko wrote:
>>> On Tue, May 26, 2020 at 09:39:13AM +0200, Lukas Wunner wrote:
>>>> On Mon, May 25, 2020 at 04:21:43PM +0300, Andy Shevchenko wrote:
>>>>> Tsuchiya Yuto, I'm going to apply this series as preparatory to my
>>>>> WIP patch in topic/spi/reload branch in my kernel tree on GitHub,
>>>>> so, it would be possible to see if this + my patch fixes crashes
>>>>> on removal. Though, please test this separately from my stuff to
>>>>> clarify if it fixes or not issue you have seen.
>>>> You also need to cherry-pick commit 84855678add8 ("spi: Fix controller
>>>> unregister order") from spi/for-next onto your topic/spi/reload branch
>>>> for reloading to work correctly.
>>>>
>>>> Alternatively, rebase your topic/spi/reload branch and redo the merge
>>>> from spi/for-next.  (You've merged spi/for-next into your branch on
>>>> May 14, but the commit was applied by Mark on May 20.)
>>> Ah, right. Will do it soon.
>>
>> I also built a kernel against your branch topic/spi/reload
>> (permalink: https://github.com/andy-shev/linux/tree/55cb78d5a752). The
>> result is the same as only applying this series; so, to fix the NULL pointer
>> dereference that I mentioned in bugzilla [2], only this series is required.
>>
>> Also, I want to make sure that what you tried in that branch is fixing
>> the NULL pointer dereference on spi_pxa2xx_platform module removal when
>> touch input crashed, not fixing the touch input crashing itself?
>
> Yes, my aim was to fix the SPI module reload issue. While the applied patch
> from Lukas does a huge improvement, there are still issues with ordering (you
> probably will never see them, though it's still possible based on the code).
>
> So, as far as I understood, the touch still able to come into position where
> it's not anymore responsive. Is it correct?

Yes, the touch still able to come into non-working state after every s2idle,
but always can be resurrected by reloading spi_pxa2xx_platform.

What this series fixed is the following thing:
- without this series: reloading spi_pxa2xx_platform resurrects touch
  input with causing NULL pointer dereference (system still operational
  after this anyway)
- with this series: reloading spi_pxa2xx_platform resurrects touch input
  *without* causing NULL pointer dereference

Let me know if any further info is required.
>
>> [1] https://bugzilla.kernel.org/show_bug.cgi?id=206403
>> [2] https://bugzilla.kernel.org/show_bug.cgi?id=206403#c1
>