mm: page_alloc: ignore init_on_free=1 for debug_pagealloc=1

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: Sergei Trofimovich <slyfox@gentoo.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -786,32 +786,36 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
  */
 void init_mem_debugging_and_hardening(void)
 {
+	bool page_poisoning_requested = false;
+
+#ifdef CONFIG_PAGE_POISONING
+	/*
+	 * Page poisoning is debug page alloc for some arches. If
+	 * either of those options are enabled, enable poisoning.
+	 */
+	if (page_poisoning_enabled() ||
+	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
+	      debug_pagealloc_enabled())) {
+		static_branch_enable(&_page_poisoning_enabled);
+		page_poisoning_requested = true;
+	}
+#endif
+
 	if (_init_on_alloc_enabled_early) {
-		if (page_poisoning_enabled())
+		if (page_poisoning_requested)
 			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
 				"will take precedence over init_on_alloc\n");
 		else
 			static_branch_enable(&init_on_alloc);
 	}
 	if (_init_on_free_enabled_early) {
-		if (page_poisoning_enabled())
+		if (page_poisoning_requested)
 			pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
 				"will take precedence over init_on_free\n");
 		else
 			static_branch_enable(&init_on_free);
 	}
 
-#ifdef CONFIG_PAGE_POISONING
-	/*
-	 * Page poisoning is debug page alloc for some arches. If
-	 * either of those options are enabled, enable poisoning.
-	 */
-	if (page_poisoning_enabled() ||
-	     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
-	      debug_pagealloc_enabled()))
-		static_branch_enable(&_page_poisoning_enabled);
-#endif
-
 #ifdef CONFIG_DEBUG_PAGEALLOC
 	if (!debug_pagealloc_enabled())
 		return;