mm: uninitialized struct page poisoning sanity checking

During boot we poison struct page memory in order to ensure that no one
is accessing this memory until the struct pages are initialized in
__init_single_page().

This patch adds more scrutiny to this checking by making sure that flags
do not equal the poison pattern when they are accessed.  The pattern is
all ones.

Since node id is also stored in struct page, and may be accessed quite
early, we add this enforcement into page_to_nid() function as well.
Note, this is applicable only when NODE_NOT_IN_PAGE_FLAGS=n

[[email protected]: v4]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Pavel Tatashin <[email protected]>
Reviewed-by: Ingo Molnar <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Steven Sistare <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Pavel Tatashin

include/linux/mm.h

@@ -903,7 +903,9 @@ extern int page_to_nid(const struct page *page);
 #else
 static inline int page_to_nid(const struct page *page)
 {
-	return (page->flags >> NODES_PGSHIFT) & NODES_MASK;
+	struct page *p = (struct page *)page;
+
+	return (PF_POISONED_CHECK(p)->flags >> NODES_PGSHIFT) & NODES_MASK;
 }
 #endif
 

include/linux/page-flags.h

@@ -156,9 +156,18 @@ static __always_inline int PageCompound(struct page *page)
 	return test_bit(PG_head, &page->flags) || PageTail(page);
 }
 
+#define	PAGE_POISON_PATTERN	-1l
+static inline int PagePoisoned(const struct page *page)
+{
+	return page->flags == PAGE_POISON_PATTERN;
+}
+
 /*
  * Page flags policies wrt compound pages
  *
+ * PF_POISONED_CHECK
+ *     check if this struct page poisoned/uninitialized
+ *
  * PF_ANY:
  *     the page flag is relevant for small, head and tail pages.
  *
@@ -176,17 +185,20 @@ static __always_inline int PageCompound(struct page *page)
  * PF_NO_COMPOUND:
  *     the page flag is not relevant for compound pages.
  */
-#define PF_ANY(page, enforce)	page
-#define PF_HEAD(page, enforce)	compound_head(page)
+#define PF_POISONED_CHECK(page) ({					\
+		VM_BUG_ON_PGFLAGS(PagePoisoned(page), page);		\
+		page; })
+#define PF_ANY(page, enforce)	PF_POISONED_CHECK(page)
+#define PF_HEAD(page, enforce)	PF_POISONED_CHECK(compound_head(page))
 #define PF_ONLY_HEAD(page, enforce) ({					\
 		VM_BUG_ON_PGFLAGS(PageTail(page), page);		\
-		page;})
+		PF_POISONED_CHECK(page); })
 #define PF_NO_TAIL(page, enforce) ({					\
 		VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);	\
-		compound_head(page);})
+		PF_POISONED_CHECK(compound_head(page)); })
 #define PF_NO_COMPOUND(page, enforce) ({				\
 		VM_BUG_ON_PGFLAGS(enforce && PageCompound(page), page);	\
-		page;})
+		PF_POISONED_CHECK(page); })
 
 /*
  * Macros to create function definitions for page flags

mm/memblock.c

@@ -1345,7 +1345,7 @@ void * __init memblock_virt_alloc_try_nid_raw(
 					   min_addr, max_addr, nid);
 #ifdef CONFIG_DEBUG_VM
 	if (ptr && size > 0)
-		memset(ptr, 0xff, size);
+		memset(ptr, PAGE_POISON_PATTERN, size);
 #endif
 	return ptr;
 }