smp_mb__{before,after}_atomic(): update Documentation

[sfrench/cifs-2.6.git] / Documentation / memory-barriers.txt

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index ec3b5865c1bec7e5b051b33be1f4805fff222b4e..7146da06169316eedad399c9e1ac553d3623182a 100644 (file)
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1868,12 +1868,16 @@ There are some more advanced barrier functions:
  (*) smp_mb__before_atomic();
  (*) smp_mb__after_atomic();
 
-     These are for use with atomic (such as add, subtract, increment and
-     decrement) functions that don't return a value, especially when used for
-     reference counting.  These functions do not imply memory barriers.
-
-     These are also used for atomic bitop functions that do not return a
-     value (such as set_bit and clear_bit).
+     These are for use with atomic RMW functions that do not imply memory
+     barriers, but where the code needs a memory barrier. Examples for atomic
+     RMW functions that do not imply are memory barrier are e.g. add,
+     subtract, (failed) conditional operations, _relaxed functions,
+     but not atomic_read or atomic_set. A common example where a memory
+     barrier may be required is when atomic ops are used for reference
+     counting.
+
+     These are also used for atomic RMW bitop functions that do not imply a
+     memory barrier (such as set_bit and clear_bit).
 
      As an example, consider a piece of code that marks an object as being dead
      and then decrements the object's reference count: