[PATCH v6 08/37] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid obj_ext creation

[Suren Baghdasaryan]

Slab extension objects can't be allocated before slab infrastructure is
initialized. Some caches, like kmem_cache and kmem_cache_node, are created
before slab infrastructure is initialized. Objects from these caches can't
have extension objects. Introduce SLAB_NO_OBJ_EXT slab flag to mark these
caches and avoid creating extensions for objects allocated from these
slabs.

Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 include/linux/slab.h | 10 ++++++++++
 mm/slub.c            |  5 +++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index e53cbfa18325..68ff754b85a4 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -56,6 +56,9 @@ enum _slab_flag_bits {
 #endif
 	_SLAB_OBJECT_POISON,
 	_SLAB_CMPXCHG_DOUBLE,
+#ifdef CONFIG_SLAB_OBJ_EXT
+	_SLAB_NO_OBJ_EXT,
+#endif
 	_SLAB_FLAGS_LAST_BIT
 };
 
@@ -202,6 +205,13 @@ enum _slab_flag_bits {
 #endif
 #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
 
+/* Slab created using create_boot_cache */
+#ifdef CONFIG_SLAB_OBJ_EXT
+#define SLAB_NO_OBJ_EXT		__SLAB_FLAG_BIT(_SLAB_NO_OBJ_EXT)
+#else
+#define SLAB_NO_OBJ_EXT		__SLAB_FLAG_UNUSED
+#endif
+
 /*
  * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
  *
diff --git a/mm/slub.c b/mm/slub.c
index 2cb53642a091..666dcc3b8a26 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5693,7 +5693,8 @@ void __init kmem_cache_init(void)
 		node_set(node, slab_nodes);
 
 	create_boot_cache(kmem_cache_node, "kmem_cache_node",
-		sizeof(struct kmem_cache_node), SLAB_HWCACHE_ALIGN, 0, 0);
+			sizeof(struct kmem_cache_node),
+			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
 
 	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
 
@@ -5703,7 +5704,7 @@ void __init kmem_cache_init(void)
 	create_boot_cache(kmem_cache, "kmem_cache",
 			offsetof(struct kmem_cache, node) +
 				nr_node_ids * sizeof(struct kmem_cache_node *),
-		       SLAB_HWCACHE_ALIGN, 0, 0);
+			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
 
 	kmem_cache = bootstrap(&boot_kmem_cache);
 	kmem_cache_node = bootstrap(&boot_kmem_cache_node);
-- 
2.44.0.291.gc1ea87d7ee-goog