On !ARCH_SUPPORTS_DEBUG_PAGEALLOC (like ia64) debug_pagealloc=1 implies
page_poison=on:

    if (page_poisoning_enabled() ||
         (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
          debug_pagealloc_enabled()))
            static_branch_enable(&_page_poisoning_enabled);

page_poison=on needs to override init_on_free=1.

Before the change it did not work as expected for the following case:
- have PAGE_POISONING=y
- have page_poison unset
- have !ARCH_SUPPORTS_DEBUG_PAGEALLOC arch (like ia64)
- have init_on_free=1
- have debug_pagealloc=1

That way we get both keys enabled:
- static_branch_enable(&init_on_free);
- static_branch_enable(&_page_poisoning_enabled);

which leads to poisoned pages returned for __GFP_ZERO pages.

After the change we execute only:
- static_branch_enable(&_page_poisoning_enabled);
  and ignore init_on_free=1.

Link: https://lkml.kernel.org/r/20210329222555.3077928-1-slyfox@gentoo.org
Link: https://lkml.org/lkml/2021/3/26/443
Fixes: 8db26a3d ("mm, page_poison: use static key more efficiently")
Signed-off-by: NSergei Trofimovich <slyfox@gentoo.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>