s390/spinlock: use correct barriers

_raw_write_lock_wait first sets the high order bit to indicate a
pending writer and then waits for the reader to drop to zero.
smp_rmb by definition only orders reads against reads. Let's use
a full smp_mb instead. As right now smp_rmb is implemented
as full serialization, this needs no stable backport, but this
patch will be necessary if we reimplement smp_rmb.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index d6c9991f7797..427aa44b3505 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -197,7 +197,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int prev)
                 }
                 old = ACCESS_ONCE(rw->lock);
                 owner = ACCESS_ONCE(rw->owner);
-                smp_rmb();
+                smp_mb();
                 if ((int) old >= 0) {
                         prev = __RAW_LOCK(&rw->lock, 0x80000000, __RAW_OP_OR);
                         old = prev;
@@ -231,7 +231,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
                     _raw_compare_and_swap(&rw->lock, old, old | 0x80000000))
                         prev = old;
                 else
-                        smp_rmb();
+                        smp_mb();
                 if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
                         break;
                 if (MACHINE_HAS_CAD)