locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()

Please do not apply this to mainline directly, instead please re-run the
coccinelle script shown below and apply its output.

For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't harmful, and changing them results in
churn.

However, for some features, the read/write distinction is critical to
correct operation. To distinguish these cases, separate read/write
accessors must be used. This patch migrates (most) remaining
ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following
coccinelle script:

----
// Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and
// WRITE_ONCE()

// $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch

virtual patch

@ depends on patch @
expression E1, E2;
@@

- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)

@ depends on patch @
expression E;
@@

- ACCESS_ONCE(E)
+ READ_ONCE(E)
----

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/s390/lib/spinlock.c

@@ -162,8 +162,8 @@ void _raw_read_lock_wait(arch_rwlock_t *rw)
 				smp_yield_cpu(~owner);
 			count = spin_retry;
 		}
-		old = ACCESS_ONCE(rw->lock);
-		owner = ACCESS_ONCE(rw->owner);
+		old = READ_ONCE(rw->lock);
+		owner = READ_ONCE(rw->owner);
 		if (old < 0)
 			continue;
 		if (__atomic_cmpxchg_bool(&rw->lock, old, old + 1))
@@ -178,7 +178,7 @@ int _raw_read_trylock_retry(arch_rwlock_t *rw)
 	int old;
 
 	while (count-- > 0) {
-		old = ACCESS_ONCE(rw->lock);
+		old = READ_ONCE(rw->lock);
 		if (old < 0)
 			continue;
 		if (__atomic_cmpxchg_bool(&rw->lock, old, old + 1))
@@ -202,8 +202,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, int prev)
 				smp_yield_cpu(~owner);
 			count = spin_retry;
 		}
-		old = ACCESS_ONCE(rw->lock);
-		owner = ACCESS_ONCE(rw->owner);
+		old = READ_ONCE(rw->lock);
+		owner = READ_ONCE(rw->owner);
 		smp_mb();
 		if (old >= 0) {
 			prev = __RAW_LOCK(&rw->lock, 0x80000000, __RAW_OP_OR);
@@ -230,8 +230,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
 				smp_yield_cpu(~owner);
 			count = spin_retry;
 		}
-		old = ACCESS_ONCE(rw->lock);
-		owner = ACCESS_ONCE(rw->owner);
+		old = READ_ONCE(rw->lock);
+		owner = READ_ONCE(rw->owner);
 		if (old >= 0 &&
 		    __atomic_cmpxchg_bool(&rw->lock, old, old | 0x80000000))
 			prev = old;
@@ -251,7 +251,7 @@ int _raw_write_trylock_retry(arch_rwlock_t *rw)
 	int old;
 
 	while (count-- > 0) {
-		old = ACCESS_ONCE(rw->lock);
+		old = READ_ONCE(rw->lock);
 		if (old)
 			continue;
 		if (__atomic_cmpxchg_bool(&rw->lock, 0, 0x80000000))