locking/qspinlock: Re-order code

Flip the branch condition after atomic_fetch_or_acquire(_Q_PENDING_VAL)
such that we loose the indent. This also result in a more natural code
flow IMO.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: andrea.parri@amarulasolutions.com
Cc: longman@redhat.com
Link: https://lkml.kernel.org/r/20181003130257.156322446@infradead.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/qspinlock.c

@@ -330,11 +330,19 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	 * 0,0,1 -> 0,1,1 ; pending
 	 */
 	val = atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val);
-	if (!(val & ~_Q_LOCKED_MASK)) {
+	/*
+	 * If we observe any contention; undo and queue.
+	 */
+	if (unlikely(val & ~_Q_LOCKED_MASK)) {
+		if (!(val & _Q_PENDING_MASK))
+			clear_pending(lock);
+		goto queue;
+	}
+
 	/*
 	 * We're pending, wait for the owner to go away.
 	 *
-		 * *,1,1 -> *,1,0
+	 * 0,1,1 -> 0,1,0
 	 *
 	 * this wait loop must be a load-acquire such that we match the
 	 * store-release that clears the locked bit and create lock
@@ -342,27 +350,17 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	 * clear_pending_set_locked() implementations imply full
 	 * barriers.
 	 */
-		if (val & _Q_LOCKED_MASK) {
-			atomic_cond_read_acquire(&lock->val,
-						 !(VAL & _Q_LOCKED_MASK));
-		}
+	if (val & _Q_LOCKED_MASK)
+		atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK));
 
 	/*
 	 * take ownership and clear the pending bit.
 	 *
-		 * *,1,0 -> *,0,1
+	 * 0,1,0 -> 0,0,1
 	 */
 	clear_pending_set_locked(lock);
 	qstat_inc(qstat_lock_pending, true);
 	return;
-	}
-
-	/*
-	 * If pending was clear but there are waiters in the queue, then
-	 * we need to undo our setting of pending before we queue ourselves.
-	 */
-	if (!(val & _Q_PENDING_MASK))
-		clear_pending(lock);
 
 	/*
 	 * End of pending bit optimistic spinning and beginning of MCS