doc/RCU: fix pseudocode in rcuref.txt

atomic_inc_not_zero(v) return 0 if *v = 0.
use spin_lock instead of write_lock for update lock.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 451de2a..4202ad0 100644 (file)
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -29,9 +29,9 @@ release_referenced()                  delete()
                                        }
 
 If this list/array is made lock free using RCU as in changing the
-write_lock() in add() and delete() to spin_lock and changing read_lock
-in search_and_reference to rcu_read_lock(), the atomic_get in
-search_and_reference could potentially hold reference to an element which
+write_lock() in add() and delete() to spin_lock() and changing read_lock()
+in search_and_reference() to rcu_read_lock(), the atomic_inc() in
+search_and_reference() could potentially hold reference to an element which
 has already been deleted from the list/array.  Use atomic_inc_not_zero()
 in this scenario as follows:
 
@@ -40,20 +40,20 @@ add()                                       search_and_reference()
 {                                      {
     alloc_object                           rcu_read_lock();
     ...                                            search_for_element
-    atomic_set(&el->rc, 1);                if (atomic_inc_not_zero(&el->rc)) {
-    write_lock(&list_lock);                    rcu_read_unlock();
+    atomic_set(&el->rc, 1);                if (!atomic_inc_not_zero(&el->rc)) {
+    spin_lock(&list_lock);                     rcu_read_unlock();
                                                return FAIL;
     add_element                                    }
     ...                                            ...
-    write_unlock(&list_lock);              rcu_read_unlock();
+    spin_unlock(&list_lock);               rcu_read_unlock();
 }                                      }
 3.                                     4.
 release_referenced()                   delete()
 {                                      {
-    ...                                            write_lock(&list_lock);
+    ...                                            spin_lock(&list_lock);
     if (atomic_dec_and_test(&el->rc))       ...
         call_rcu(&el->head, el_free);       delete_element
-    ...                                     write_unlock(&list_lock);
+    ...                                     spin_unlock(&list_lock);
 }                                          ...
                                            if (atomic_dec_and_test(&el->rc))
                                                call_rcu(&el->head, el_free);