Re: Regression with v5.18-rc1 tag on STM32F7 and STM32H7 based boards

[Patrice CHOTARD]

Hi Hugh

On 4/5/22 21:59, Hugh Dickins wrote:
> On Tue, 5 Apr 2022, Patrice CHOTARD wrote:
>>
>> We found an issue with last kernel tag v5.18-rc1 on stm32f746-disco and 
>> stm32h743-disco boards (ARMV7-M SoCs).
>>
>> Kernel hangs when executing SetPageUptodate(ZERO_PAGE(0)); in mm/filemap.c.
>>
>> By reverting commit 56a8c8eb1eaf ("tmpfs: do not allocate pages on read"), 
>> kernel boots without any issue.
> 
> Sorry about that, thanks a lot for finding.
> 
> I see that arch/arm/configs/stm32_defconfig says CONFIG_MMU is not set:
> please confirm that is the case here.

Yes i confirm, CONFIG_MMU is not set.



> 
> Yes, it looks as if NOMMU platforms are liable to have a bogus (that's my
> reading, but it may be unfair) definition for ZERO_PAGE(vaddr), and I was
> walking on ice to touch it without regard for !CONFIG_MMU.
> 
> CONFIG_SHMEM depends on CONFIG_MMU, so that PageUptodate is only needed
> when CONFIG_MMU.
> 
> Easily fixed by an #ifdef CONFIG_MMU there in mm/filemap.c, but I'll hunt
> around (again) for a better place to do it - though I won't want to touch
> all the architectures for it.  I'll post later today.

I did a quick test on my side, and yes, adding #ifdef CONFIG_MMU around 
SetPageUptodate(ZERO_PAGE(0)); allows to boot the boards.

Thanks
Patrice
> 
> Hugh