[PATCH v4 08/36] mm: introduce __GFP_NO_OBJ_EXT flag to selectively prevent slabobj_ext creation

[Suren Baghdasaryan]

Introduce __GFP_NO_OBJ_EXT flag in order to prevent recursive allocations
when allocating slabobj_ext on a slab.

Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/gfp_types.h | 11 +++++++++++
 mm/slub.c                 |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
index 868c8fb1bbc1..e36e168d8cfd 100644
--- a/include/linux/gfp_types.h
+++ b/include/linux/gfp_types.h
@@ -52,6 +52,9 @@ enum {
 #endif
 #ifdef CONFIG_LOCKDEP
 	___GFP_NOLOCKDEP_BIT,
+#endif
+#ifdef CONFIG_SLAB_OBJ_EXT
+	___GFP_NO_OBJ_EXT_BIT,
 #endif
 	___GFP_LAST_BIT
 };
@@ -93,6 +96,11 @@ enum {
 #else
 #define ___GFP_NOLOCKDEP	0
 #endif
+#ifdef CONFIG_SLAB_OBJ_EXT
+#define ___GFP_NO_OBJ_EXT       BIT(___GFP_NO_OBJ_EXT_BIT)
+#else
+#define ___GFP_NO_OBJ_EXT       0
+#endif
 
 /*
  * Physical address zone modifiers (see linux/mmzone.h - low four bits)
@@ -133,12 +141,15 @@ enum {
  * node with no fallbacks or placement policy enforcements.
  *
  * %__GFP_ACCOUNT causes the allocation to be accounted to kmemcg.
+ *
+ * %__GFP_NO_OBJ_EXT causes slab allocation to have no object extension.
  */
 #define __GFP_RECLAIMABLE ((__force gfp_t)___GFP_RECLAIMABLE)
 #define __GFP_WRITE	((__force gfp_t)___GFP_WRITE)
 #define __GFP_HARDWALL   ((__force gfp_t)___GFP_HARDWALL)
 #define __GFP_THISNODE	((__force gfp_t)___GFP_THISNODE)
 #define __GFP_ACCOUNT	((__force gfp_t)___GFP_ACCOUNT)
+#define __GFP_NO_OBJ_EXT   ((__force gfp_t)___GFP_NO_OBJ_EXT)
 
 /**
  * DOC: Watermark modifiers
diff --git a/mm/slub.c b/mm/slub.c
index 76fb600fbc80..ca803b2949fc 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1899,6 +1899,8 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 	void *vec;
 
 	gfp &= ~OBJCGS_CLEAR_MASK;
+	/* Prevent recursive extension vector allocation */
+	gfp |= __GFP_NO_OBJ_EXT;
 	vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
 			   slab_nid(slab));
 	if (!vec)
-- 
2.44.0.rc0.258.g7320e95886-goog