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authorNick Piggin <nickpiggin@yahoo.com.au>2005-11-13 16:07:24 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2005-11-13 18:14:16 -0800
commit4a6dae6d382e9edf3ff440b819e554ed706359bc (patch)
tree2945a5095973e2ecf05b503d6deb859083045b8e /Documentation/atomic_ops.txt
parent53e86b91b7ae66d4c2757195cbd42e00d9199cf2 (diff)
downloadlinux-linaro-stable-4a6dae6d382e9edf3ff440b819e554ed706359bc.tar.gz
[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>
Diffstat (limited to 'Documentation/atomic_ops.txt')
-rw-r--r--Documentation/atomic_ops.txt15
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: