[S390] atomic: implement atomic64_dec_if_positive

Implement atomic64_dec_if_positive and add missing system.h header
include.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/include/asm/atomic.h b/arch/s390/include/asm/atomic.h
index 451bfbb..76daea1 100644 (file)
--- a/arch/s390/include/asm/atomic.h
+++ b/arch/s390/include/asm/atomic.h
@@ -15,6 +15,7 @@
 
 #include <linux/compiler.h>
 #include <linux/types.h>
+#include <asm/system.h>
 
 #define ATOMIC_INIT(i)  { (i) }
 
@@ -274,6 +275,7 @@ static inline void atomic64_clear_mask(unsigned long long mask, atomic64_t *v)
 static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
 {
        long long c, old;
+
        c = atomic64_read(v);
        for (;;) {
                if (unlikely(c == u))
@@ -286,6 +288,23 @@ static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
        return c != u;
 }
 
+static inline long long atomic64_dec_if_positive(atomic64_t *v)
+{
+       long long c, old, dec;
+
+       c = atomic64_read(v);
+       for (;;) {
+               dec = c - 1;
+               if (unlikely(dec < 0))
+                       break;
+               old = atomic64_cmpxchg((v), c, dec);
+               if (likely(old == c))
+                       break;
+               c = old;
+       }
+       return dec;
+}
+
 #define atomic64_add(_i, _v)           atomic64_add_return(_i, _v)
 #define atomic64_add_negative(_i, _v)  (atomic64_add_return(_i, _v) < 0)
 #define atomic64_inc(_v)               atomic64_add_return(1, _v)