mm: enable page poisoning early at boot

On SPARSEMEM systems page poisoning is enabled after buddy is up, because
of the dependency on page extension init.  This causes the pages released
by free_all_bootmem not to be poisoned.  This either delays or misses the
identification of some issues because the pages have to undergo another
cycle of alloc-free-alloc for any corruption to be detected.

Enable page poisoning early by getting rid of the PAGE_EXT_DEBUG_POISON
flag.  Since all the free pages will now be poisoned, the flag need not be
verified before checking the poison during an alloc.

Link: http://lkml.kernel.org/r/1490358246-11001-1-git-send-email-vinmenon@codeaurora.org
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Acked-by: Laura Abbott <labbott@redhat.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

3 files changed, 15 insertions, 78 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 975b081b5c6c..e025e620053d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1688,10 +1688,10 @@ static inline int check_new_page(struct page *page)
 	return 1;
 }
 
-static inline bool free_pages_prezeroed(bool poisoned)
+static inline bool free_pages_prezeroed(void)
 {
 	return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
-		page_poisoning_enabled() && poisoned;
+		page_poisoning_enabled();
 }
 
 #ifdef CONFIG_DEBUG_VM
@@ -1745,17 +1745,10 @@ static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags
 							unsigned int alloc_flags)
 {
 	int i;
-	bool poisoned = true;
-
-	for (i = 0; i < (1 << order); i++) {
-		struct page *p = page + i;
-		if (poisoned)
-			poisoned &= page_is_poisoned(p);
-	}
 
 	post_alloc_hook(page, order, gfp_flags);
 
-	if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))
+	if (!free_pages_prezeroed() && (gfp_flags & __GFP_ZERO))
 		for (i = 0; i < (1 << order); i++)
 			clear_highpage(page + i);
 
diff --git a/mm/page_ext.c b/mm/page_ext.c
index 121dcffc4ec1..fc3e7ffd189e 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -59,9 +59,6 @@
 
 static struct page_ext_operations *page_ext_ops[] = {
 	&debug_guardpage_ops,
-#ifdef CONFIG_PAGE_POISONING
-	&page_poisoning_ops,
-#endif
 #ifdef CONFIG_PAGE_OWNER
 	&page_owner_ops,
 #endif
diff --git a/mm/page_poison.c b/mm/page_poison.c
index 2e647c65916b..be19e989ccff 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -6,7 +6,6 @@
 #include <linux/poison.h>
 #include <linux/ratelimit.h>
 
-static bool __page_poisoning_enabled __read_mostly;
 static bool want_page_poisoning __read_mostly;
 
 static int early_page_poison_param(char *buf)
@@ -19,74 +18,21 @@ early_param("page_poison", early_page_poison_param);
 
 bool page_poisoning_enabled(void)
 {
-	return __page_poisoning_enabled;
-}
-
-static bool need_page_poisoning(void)
-{
-	return want_page_poisoning;
-}
-
-static void init_page_poisoning(void)
-{
 	/*
-	 * page poisoning is debug page alloc for some arches. If either
-	 * of those options are enabled, enable poisoning
+	 * Assumes that debug_pagealloc_enabled is set before
+	 * free_all_bootmem.
+	 * Page poisoning is debug page alloc for some arches. If
+	 * either of those options are enabled, enable poisoning.
 	 */
-	if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
-		if (!want_page_poisoning && !debug_pagealloc_enabled())
-			return;
-	} else {
-		if (!want_page_poisoning)
-			return;
-	}
-
-	__page_poisoning_enabled = true;
-}
-
-struct page_ext_operations page_poisoning_ops = {
-	.need = need_page_poisoning,
-	.init = init_page_poisoning,
-};
-
-static inline void set_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	if (unlikely(!page_ext))
-		return;
-
-	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-static inline void clear_page_poison(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	if (unlikely(!page_ext))
-		return;
-
-	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
-}
-
-bool page_is_poisoned(struct page *page)
-{
-	struct page_ext *page_ext;
-
-	page_ext = lookup_page_ext(page);
-	if (unlikely(!page_ext))
-		return false;
-
-	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
+	return (want_page_poisoning ||
+		(!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
+		debug_pagealloc_enabled()));
 }
 
 static void poison_page(struct page *page)
 {
 	void *addr = kmap_atomic(page);
 
-	set_page_poison(page);
 	memset(addr, PAGE_POISON, PAGE_SIZE);
 	kunmap_atomic(addr);
 }
@@ -140,12 +86,13 @@ static void unpoison_page(struct page *page)
 {
 	void *addr;
 
-	if (!page_is_poisoned(page))
-		return;
-
 	addr = kmap_atomic(page);
+	/*
+	 * Page poisoning when enabled poisons each and every page
+	 * that is freed to buddy. Thus no extra check is done to
+	 * see if a page was posioned.
+	 */
 	check_poison_mem(addr, PAGE_SIZE);
-	clear_page_poison(page);
 	kunmap_atomic(addr);
 }