s390/mm: make use of atomic_fetch_xor()

Make use of atomic_fetch_xor() instead of an atomic_cmpxchg() loop to
implement atomic_xor_bits() (aka atomic_xor_return()). This makes the C
code more readable and in addition generates better code, since for z196
and newer a single lax instruction is generated instead of a cmpxchg()
loop.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 0f68b7257e08def113fa1633439028bb1f4b4966..66ab68db98428cfeec1e5fb10b6a13f4288230d3 100644 (file)
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -133,13 +133,7 @@ err_p4d:
 
 static inline unsigned int atomic_xor_bits(atomic_t *v, unsigned int bits)
 {
-       unsigned int old, new;
-
-       do {
-               old = atomic_read(v);
-               new = old ^ bits;
-       } while (atomic_cmpxchg(v, old, new) != old);
-       return new;
+       return atomic_fetch_xor(bits, v) ^ bits;
 }
 
 #ifdef CONFIG_PGSTE