Linus Walleij linus.walleij@linaro.org writes:
On Mon, Dec 14, 2020 at 10:21 AM David Hildenbrand david@redhat.com 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.