X-Git-Url: http://git.rot13.org/?a=blobdiff_plain;f=Documentation%2FRCU%2Frcuref.txt;h=451de2ad8329022e3164f26cfa138f9a05dc1d33;hb=f9a14399aea13830d8af6798a53207bb0a900945;hp=a23fee66064df4ff6770e9be02f79af4a0397745;hpb=3874b98c655b9490bea1cf9c7697d5dc5338376f;p=powerpc.git

diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index a23fee6606..451de2ad83 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -1,74 +1,66 @@
-Refcounter framework for elements of lists/arrays protected by
-RCU.
+Reference-count design for elements of lists/arrays protected by RCU.
 
-Refcounting on elements of  lists which are protected by traditional
-reader/writer spinlocks or semaphores are straight forward as in:
+Reference counting on elements of lists which are protected by traditional
+reader/writer spinlocks or semaphores are straightforward:
 
-1.					2.
-add()					search_and_reference()
-{					{
-	alloc_object				read_lock(&list_lock);
-	...					search_for_element
-	atomic_set(&el->rc, 1);			atomic_inc(&el->rc);
-	write_lock(&list_lock);			...
-	add_element				read_unlock(&list_lock);
-	...					...
-	write_unlock(&list_lock);	}
+1.				2.
+add()				search_and_reference()
+{				{
+    alloc_object		    read_lock(&list_lock);
+    ...				    search_for_element
+    atomic_set(&el->rc, 1);	    atomic_inc(&el->rc);
+    write_lock(&list_lock);	     ...
+    add_element			    read_unlock(&list_lock);
+    ...				    ...
+    write_unlock(&list_lock);	}
 }
 
 3.					4.
 release_referenced()			delete()
 {					{
-	...				write_lock(&list_lock);
-	atomic_dec(&el->rc, relfunc)	...
-	...				delete_element
-}					write_unlock(&list_lock);
- 					...
-					if (atomic_dec_and_test(&el->rc))
-						kfree(el);
-					...
+    ...					    write_lock(&list_lock);
+    atomic_dec(&el->rc, relfunc)	    ...
+    ...					    delete_element
+}					    write_unlock(&list_lock);
+ 					    ...
+					    if (atomic_dec_and_test(&el->rc))
+					        kfree(el);
+					    ...
 					}
 
-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 rcuref_get in
+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
-has already been deleted from the list/array.  rcuref_lf_get_rcu takes
-care of this scenario. search_and_reference should look as;
+has already been deleted from the list/array.  Use atomic_inc_not_zero()
+in this scenario as follows:
 
 1.					2.
 add()					search_and_reference()
 {					{
- 	alloc_object				rcu_read_lock();
-	...					search_for_element
-	atomic_set(&el->rc, 1);			if (rcuref_inc_lf(&el->rc)) {
-	write_lock(&list_lock);				rcu_read_unlock();
-							return FAIL;
-	add_element				}
-	...					...
-	write_unlock(&list_lock);		rcu_read_unlock();
+    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();
+					        return FAIL;
+    add_element				    }
+    ...					    ...
+    write_unlock(&list_lock);		    rcu_read_unlock();
 }					}
 3.					4.
 release_referenced()			delete()
 {					{
-	...				write_lock(&list_lock);
-	rcuref_dec(&el->rc, relfunc)	...
-	...				delete_element
-}					write_unlock(&list_lock);
- 					...
-					if (rcuref_dec_and_test(&el->rc))
-						call_rcu(&el->head, el_free);
-					...
+    ...					    write_lock(&list_lock);
+    if (atomic_dec_and_test(&el->rc))       ...
+        call_rcu(&el->head, el_free);       delete_element
+    ...                                     write_unlock(&list_lock);
+} 					    ...
+					    if (atomic_dec_and_test(&el->rc))
+					        call_rcu(&el->head, el_free);
+					    ...
 					}
 
-Sometimes, reference to the element need to be obtained in the
-update (write) stream.  In such cases, rcuref_inc_lf might be an overkill
-since the spinlock serialising list updates are held. rcuref_inc
-is to be used in such cases.
-For arches which do not have cmpxchg rcuref_inc_lf
-api uses a hashed spinlock implementation and the same hashed spinlock
-is acquired in all rcuref_xxx primitives to preserve atomicity.
-Note: Use rcuref_inc api only if you need to use rcuref_inc_lf on the
-refcounter atleast at one place.  Mixing rcuref_inc and atomic_xxx api
-might lead to races. rcuref_inc_lf() must be used in lockfree
-RCU critical sections only.
+Sometimes, a reference to the element needs to be obtained in the
+update (write) stream.  In such cases, atomic_inc_not_zero() might be
+overkill, since we hold the update-side spinlock.  One might instead
+use atomic_inc() in such cases.