linux-kernel - [PATCH] Doc/RCU: fix pseudocode in rcuref.txt

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Date:	Wed, 10 Sep 2008 11:01:07 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] 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@...fujitsu.com>
---
diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 451de2a..4202ad0 100644
--- 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);


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