Linus Walleij <linus.walleij@xxxxxxxxxx> writes:
> On Mon, Dec 14, 2020 at 10:21 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
>> > ARM SoC folks: please apply this directly for fixes.
>>
>> Can we come up with a Fixes: tag or has this been broken forever?
>> (assuming modern boot loaders)
>
> It's been broken forever :/
>
>> > David: just FYI if you run into more of these type of
>> > regressions. Actually the patch is unintentionally good
>> > at smoking out other bugs :D
>>
>> Thanks for CCing - I'm adding some people that ran into similar issues,
>> but not sure if the other bugreports are related (or have similar root
>> causes).
>
> Yeah we first were convinced there was something wrong with
> the patch you made but I read it over and over again and there
> is nothing wrong with it at all. It just alters the behaviour pattern of
> memory management in some apparently drastic ways.
>
> After a lot of silent crashes I finally got an external abort with
> a reasonable backtrace showing the PTE pointing to this
> modem memory and then we figured it out.
We had similar experiences with ath11k (Wi-Fi 6) and QCA6390 firmware.
So indeed commit 7fef431be9c9 ("mm/page_alloc: place pages to tail in
__free_pages_core()") is a great way to catch odd firmware or hardware
problems, which most likely would have gone unnoticed otherwise and
users would have end up experiencing random crashes.
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