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-rw-r--r--Documentation/atomic_ops.txt15
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diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index 8eedaa24f5e..f1744161ef0 100644
--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -115,6 +115,21 @@ boolean is return which indicates whether the resulting counter value
is negative. It requires explicit memory barrier semantics around the
operation.
+Finally:
+
+ int atomic_cmpxchg(atomic_t *v, int old, int new);
+
+This performs an atomic compare exchange operation on the atomic value v,
+with the given old and new values. Like all atomic_xxx operations,
+atomic_cmpxchg will only satisfy its atomicity semantics as long as all
+other accesses of *v are performed through atomic_xxx operations.
+
+atomic_cmpxchg requires explicit memory barriers around the operation.
+
+The semantics for atomic_cmpxchg are the same as those defined for 'cas'
+below.
+
+
If a caller requires memory barrier semantics around an atomic_t
operation which does not return a value, a set of interfaces are
defined which accomplish this: