[PATCH] atomic: inc_not_zero

Introduce an atomic_inc_not_zero operation.  Make this a special case of
atomic_add_unless because lockless pagecache actually wants
atomic_inc_not_negativeone due to its offset refcount.

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, 19 insertions, 0 deletions

diff --git a/include/asm-x86_64/atomic.h b/include/asm-x86_64/atomic.h
index 75c8a1e96737..0866ef67f198 100644
--- a/include/asm-x86_64/atomic.h
+++ b/include/asm-x86_64/atomic.h
@@ -362,6 +362,25 @@ static __inline__ int atomic_sub_return(int i, atomic_t *v)
 
 #define atomic_cmpxchg(v, old, new) ((int)cmpxchg(&((v)->counter), old, new))
 
+/**
+ * atomic_add_unless - add unless the number is a given value
+ * @v: pointer of type atomic_t
+ * @a: the amount to add to v...
+ * @u: ...unless v is equal to u.
+ *
+ * Atomically adds @a to @v, so long as it was not @u.
+ * Returns non-zero if @v was not @u, and zero otherwise.
+ */
+#define atomic_add_unless(v, a, u)                              \
+({                                                              \
+        int c, old;                                             \
+        c = atomic_read(v);                                     \
+        while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \
+                c = old;                                        \
+        c != (u);                                               \
+})
+#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
+
 #define atomic_inc_return(v)  (atomic_add_return(1,v))
 #define atomic_dec_return(v)  (atomic_sub_return(1,v))