[PATCH] atomic: cmpxchg

Introduce an atomic_cmpxchg operation.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index 8eedaa24f5e2..f1744161ef06 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: