1 files changed, 33 insertions, 26 deletions

diff --git a/ipc/util.c b/ipc/util.c
index e829da9ed01f..7684f41bce76 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -17,12 +17,27 @@
  *            Pavel Emelianov <xemul@openvz.org>
  *
  * General sysv ipc locking scheme:
- *  when doing ipc id lookups, take the ids->rwsem
- *      rcu_read_lock()
- *          obtain the ipc object (kern_ipc_perm)
- *          perform security, capabilities, auditing and permission checks, etc.
- *          acquire the ipc lock (kern_ipc_perm.lock) throught ipc_lock_object()
- *             perform data updates (ie: SET, RMID, LOCK/UNLOCK commands)
+ *      rcu_read_lock()
+ *          obtain the ipc object (kern_ipc_perm) by looking up the id in an idr
+ *          tree.
+ *          - perform initial checks (capabilities, auditing and permission,
+ *            etc).
+ *          - perform read-only operations, such as STAT, INFO commands.
+ *            acquire the ipc lock (kern_ipc_perm.lock) through
+ *            ipc_lock_object()
+ *              - perform data updates, such as SET, RMID commands and
+ *                mechanism-specific operations (semop/semtimedop,
+ *                msgsnd/msgrcv, shmat/shmdt).
+ *          drop the ipc lock, through ipc_unlock_object().
+ *      rcu_read_unlock()
+ *
+ *  The ids->rwsem must be taken when:
+ *      - creating, removing and iterating the existing entries in ipc
+ *        identifier sets.
+ *      - iterating through files under /proc/sysvipc/
+ *
+ *  Note that sems have a special fast path that avoids kern_ipc_perm.lock -
+ *  see sem_lock().
  */
 
 #include <linux/mm.h>
@@ -474,11 +489,6 @@ void ipc_free(void* ptr, int size)
                 kfree(ptr);
 }
 
-struct ipc_rcu {
-        struct rcu_head rcu;
-        atomic_t refcount;
-} ____cacheline_aligned_in_smp;
-
 /**
  *      ipc_rcu_alloc   -       allocate ipc and rcu space 
  *      @size: size desired
@@ -505,27 +515,24 @@ int ipc_rcu_getref(void *ptr)
         return atomic_inc_not_zero(&p->refcount);
 }
 
-/**
- * ipc_schedule_free - free ipc + rcu space
- * @head: RCU callback structure for queued work
- */
-static void ipc_schedule_free(struct rcu_head *head)
-{
-        vfree(container_of(head, struct ipc_rcu, rcu));
-}
-
-void ipc_rcu_putref(void *ptr)
+void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
 {
         struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
 
         if (!atomic_dec_and_test(&p->refcount))
                 return;
 
-        if (is_vmalloc_addr(ptr)) {
-                call_rcu(&p->rcu, ipc_schedule_free);
-        } else {
-                kfree_rcu(p, rcu);
-        }
+        call_rcu(&p->rcu, func);
+}
+
+void ipc_rcu_free(struct rcu_head *head)
+{
+        struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
+
+        if (is_vmalloc_addr(p))
+                vfree(p);
+        else
+                kfree(p);
 }
 
 /**