powerpc: qspinlock: Mark accesses to qnode lock checks

The powerpc implementation of qspinlocks will both poll and spin on the
bitlock guarding a qnode. Mark these accesses with READ_ONCE to convey
to KCSAN that polling is intentional here.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230510033117.1395895-2-rmclure@linux.ibm.com

Author: rohanmclure

arch/powerpc/lib/qspinlock.c

@@ -435,7 +435,7 @@ static __always_inline bool yield_to_prev(struct qspinlock *lock, struct qnode *
 
 	smp_rmb(); /* See __yield_to_locked_owner comment */
 
-	if (!node->locked) {
+	if (!READ_ONCE(node->locked)) {
 		yield_to_preempted(prev_cpu, yield_count);
 		spin_begin();
 		return preempted;
@@ -584,7 +584,7 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
 
 		/* Wait for mcs node lock to be released */
 		spin_begin();
-		while (!node->locked) {
+		while (!READ_ONCE(node->locked)) {
 			spec_barrier();
 
 			if (yield_to_prev(lock, node, old, paravirt))