mm/hwpoison-inject: support injecting hwpoison to free page

memory_failure() can handle free buddy page.  Support injecting hwpoison
to free page by adding is_free_buddy_page check when hwpoison filter is
disabled.

[akpm@linux-foundation.org: export is_free_buddy_page() to modules]

Link: https://lkml.kernel.org/r/20220218092052.3853-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hwpoison-inject.c

@@ -32,9 +32,9 @@ static int hwpoison_inject(void *data, u64 val)
 
 	shake_page(hpage);
 	/*
-	 * This implies unable to support non-LRU pages.
+	 * This implies unable to support non-LRU pages except free page.
 	 */
-	if (!PageLRU(hpage) && !PageHuge(p))
+	if (!PageLRU(hpage) && !PageHuge(p) && !is_free_buddy_page(p))
 		return 0;
 
 	/*

mm/page_alloc.c

@@ -9417,6 +9417,7 @@ bool is_free_buddy_page(struct page *page)
 
 	return order < MAX_ORDER;
 }
+EXPORT_SYMBOL(is_free_buddy_page);
 
 #ifdef CONFIG_MEMORY_FAILURE
 /*