1 files changed, 33 insertions, 10 deletions

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 5ff9676c1e2c..f96d13c281e8 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -23,6 +23,34 @@
 #define SLAB_CACHE_DMA          0x00004000UL    /* Use GFP_DMA memory */
 #define SLAB_STORE_USER         0x00010000UL    /* DEBUG: Store the last owner for bug hunting */
 #define SLAB_PANIC              0x00040000UL    /* Panic if kmem_cache_create() fails */
+/*
+ * SLAB_DESTROY_BY_RCU - **WARNING** READ THIS!
+ *
+ * This delays freeing the SLAB page by a grace period, it does _NOT_
+ * delay object freeing. This means that if you do kmem_cache_free()
+ * that memory location is free to be reused at any time. Thus it may
+ * be possible to see another object there in the same RCU grace period.
+ *
+ * This feature only ensures the memory location backing the object
+ * stays valid, the trick to using this is relying on an independent
+ * object validation pass. Something like:
+ *
+ *  rcu_read_lock()
+ * again:
+ *  obj = lockless_lookup(key);
+ *  if (obj) {
+ *    if (!try_get_ref(obj)) // might fail for free objects
+ *      goto again;
+ *
+ *    if (obj->key != key) { // not the object we expected
+ *      put_ref(obj);
+ *      goto again;
+ *    }
+ *  }
+ *  rcu_read_unlock();
+ *
+ * See also the comment on struct slab_rcu in mm/slab.c.
+ */
 #define SLAB_DESTROY_BY_RCU     0x00080000UL    /* Defer freeing slabs to RCU */
 #define SLAB_MEM_SPREAD         0x00100000UL    /* Spread some memory over cpuset */
 #define SLAB_TRACE              0x00200000UL    /* Trace allocations and frees */
@@ -225,9 +253,9 @@ static inline void *kmem_cache_alloc_node(struct kmem_cache *cachep,
  * request comes from.
  */
 #if defined(CONFIG_DEBUG_SLAB) || defined(CONFIG_SLUB)
-extern void *__kmalloc_track_caller(size_t, gfp_t, void*);
+extern void *__kmalloc_track_caller(size_t, gfp_t, unsigned long);
 #define kmalloc_track_caller(size, flags) \
-        __kmalloc_track_caller(size, flags, __builtin_return_address(0))
+        __kmalloc_track_caller(size, flags, _RET_IP_)
 #else
 #define kmalloc_track_caller(size, flags) \
         __kmalloc(size, flags)
@@ -243,10 +271,10 @@ extern void *__kmalloc_track_caller(size_t, gfp_t, void*);
  * allocation request comes from.
  */
 #if defined(CONFIG_DEBUG_SLAB) || defined(CONFIG_SLUB)
-extern void *__kmalloc_node_track_caller(size_t, gfp_t, int, void *);
+extern void *__kmalloc_node_track_caller(size_t, gfp_t, int, unsigned long);
 #define kmalloc_node_track_caller(size, flags, node) \
         __kmalloc_node_track_caller(size, flags, node, \
-                        __builtin_return_address(0))
+                        _RET_IP_)
 #else
 #define kmalloc_node_track_caller(size, flags, node) \
         __kmalloc_node(size, flags, node)
@@ -257,7 +285,7 @@ extern void *__kmalloc_node_track_caller(size_t, gfp_t, int, void *);
 #define kmalloc_node_track_caller(size, flags, node) \
         kmalloc_track_caller(size, flags)
 
-#endif /* DEBUG_SLAB */
+#endif /* CONFIG_NUMA */
 
 /*
  * Shortcuts
@@ -288,9 +316,4 @@ static inline void *kzalloc_node(size_t size, gfp_t flags, int node)
         return kmalloc_node(size, flags | __GFP_ZERO, node);
 }
 
-#ifdef CONFIG_SLABINFO
-extern const struct seq_operations slabinfo_op;
-ssize_t slabinfo_write(struct file *, const char __user *, size_t, loff_t *);
-#endif
-
 #endif  /* _LINUX_SLAB_H */