slab,rcu: don't assume the size of struct rcu_head

The size of struct rcu_head may be changed. When it becomes larger,
it may pollute the data after struct slab.

Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

1 files changed, 21 insertions, 18 deletions

diff --git a/mm/slab.c b/mm/slab.c
index 37961d1f584f..52cf0b4634d4 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -191,22 +191,6 @@ typedef unsigned int kmem_bufctl_t;
 #define SLAB_LIMIT      (((kmem_bufctl_t)(~0U))-3)
 
 /*
- * struct slab
- *
- * Manages the objs in a slab. Placed either at the beginning of mem allocated
- * for a slab, or allocated from an general cache.
- * Slabs are chained into three list: fully used, partial, fully free slabs.
- */
-struct slab {
-        struct list_head list;
-        unsigned long colouroff;
-        void *s_mem;            /* including colour offset */
-        unsigned int inuse;     /* num of objs active in slab */
-        kmem_bufctl_t free;
-        unsigned short nodeid;
-};
-
-/*
  * struct slab_rcu
  *
  * slab_destroy on a SLAB_DESTROY_BY_RCU cache uses this structure to
@@ -219,8 +203,6 @@ struct slab {
  *
  * rcu_read_lock before reading the address, then rcu_read_unlock after
  * taking the spinlock within the structure expected at that address.
- *
- * We assume struct slab_rcu can overlay struct slab when destroying.
  */
 struct slab_rcu {
         struct rcu_head head;
@@ -229,6 +211,27 @@ struct slab_rcu {
 };
 
 /*
+ * struct slab
+ *
+ * Manages the objs in a slab. Placed either at the beginning of mem allocated
+ * for a slab, or allocated from an general cache.
+ * Slabs are chained into three list: fully used, partial, fully free slabs.
+ */
+struct slab {
+        union {
+                struct {
+                        struct list_head list;
+                        unsigned long colouroff;
+                        void *s_mem;            /* including colour offset */
+                        unsigned int inuse;     /* num of objs active in slab */
+                        kmem_bufctl_t free;
+                        unsigned short nodeid;
+                };
+                struct slab_rcu __slab_cover_slab_rcu;
+        };
+};
+
+/*
  * struct array_cache
  *
  * Purpose: