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Date:   Tue, 12 Jan 2021 10:53:45 +0000
From:   Guillaume Tucker <guillaume.tucker@...labora.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        kernelci-results-staging@...ups.io,
        "kernelci-results@...ups.io" <kernelci-results@...ups.io>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>, Baoquan He <bhe@...hat.com>
Subject: Re: kernelci/staging-next bisection: sleep.login on
 rk3288-rock2-square #2286-staging

On 05/01/2021 09:13, Mike Rapoport wrote:
> On Sun, Jan 03, 2021 at 03:09:14PM -0500, Andrea Arcangeli wrote:
>> Hello Mike,
>>
>> On Sun, Jan 03, 2021 at 03:47:53PM +0200, Mike Rapoport wrote:
>>> Thanks for the logs, it seems that implicitly adding reserved regions to
>>> memblock.memory wasn't that bright idea :)
>>
>> Would it be possible to somehow clean up the hack then?
>>
>> The only difference between the clean solution and the hack is that
>> the hack intended to achieved the exact same, but without adding the
>> reserved regions to memblock.memory.
> 
> I didn't consider adding reserved regions to memblock.memory as a clean
> solution, this was still a hack, but I didn't think that things are that
> fragile.
> 
> I still think we cannot rely on memblock.reserved to detect
> memory/zone/node sizes and the boot failure reported here confirms this.
>  
>> The comment on that problematic area says the reserved area cannot be
>> used for DMA because of some unexplained hw issue, and that doing so
>> prevents booting, but since the area got reserved, even with the clean
>> solution, it shouldn't have never been used for DMA?
>>
>> So I can only imagine that the physical memory region is way more
>> problematic than just for DMA. It sounds like that anything that
>> touches it, including the CPU, will hang the system, not just DMA. It
>> sounds somewhat similar to the other e820 direct mapping issue on x86?
> 
> My understanding is that the boot failed because when I implicitly added
> the reserved region to memblock.memory the memory size seen by
> free_area_init() jumped from 2G to 4G because the reserved area was close
> to 4G. The very first allocation would get a chunk from slightly below of
> 4G and as there is no real memory there, the kernel would crash.
>  
>> If you want to test the hack on the arm board to check if it boots you
>> can use the below commit:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/commit/?id=c3ea2633015104ce0df33dcddbc36f57de1392bc
> 
> My take is your solution would boot with this memory configuration, but I
> still don't think that using memblock.reserved for zone/node sizing is
> correct.

The rk3288 platform has now been failing to boot for nearly a
month on linux-next:

  https://kernelci.org/test/case/id/5ffbed0a31ad81239bc94cdb/

Until a fix or a new version of this patch is made, would it be
possible to drop it or revert it so the platform become usable
again?

Or if you want, I can make a cleaned-up version of my hack to
ignore the problematic region if you still need your patch to be
on linux-next, but that would probably be less than ideal.

Thanks,
Guillaume

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