Re: [PATCH] mm, debug_pagealloc: don't rely on static keys too early

[Qian Cai]

> On Dec 19, 2019, at 8:06 AM, Vlastimil Babka <vbabka@xxxxxxx> wrote:
> 
> Commit 96a2b03f281d ("mm, debug_pagelloc: use static keys to enable debugging")
> has introduced a static key to reduce overhead when debug_pagealloc is compiled
> in but not enabled. It relied on the assumption that jump_label_init() is
> called before parse_early_param() as in start_kernel(), so when the
> "debug_pagealloc=on" option is parsed, it is safe to enable the static key.
> 
> However, it turns out multiple architectures call parse_early_param() earlier
> from their setup_arch(). x86 also calls jump_label_init() even earlier, so no
> issue was found while testing the commit, but same is not true for e.g. ppc64
> and s390 where the kernel would not boot with debug_pagealloc=on as found by
> our QA.

This was daily tested on linux-next here for those arches and never saw an issue. Are you able to reproduce it on mainline or linux-next?