lib: posix: pthread_rwlock: Fix a racy issue

Multiple reader threads unlocking the read lock simultaneously might
cause the program hang because it's possible that no thread is
identified as the last one to active the writer thread.

To fix the issue, swap the k_sem_give sequence.

Signed-off-by: Jaxson Han <jaxson.han@arm.com>

lib/posix/rwlock.c

@@ -200,13 +200,13 @@ int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
 		k_sem_give(&rwlock->wr_sem);
 	} else {
 		/* Read unlock */
+		k_sem_give(&rwlock->rd_sem);
+
 		if (k_sem_count_get(&rwlock->rd_sem) ==
-				    (CONCURRENT_READER_LIMIT - 1)) {
+				    CONCURRENT_READER_LIMIT) {
 			/* Last read lock, unlock writer */
 			k_sem_give(&rwlock->reader_active);
 		}
-
-		k_sem_give(&rwlock->rd_sem);
 	}
 	return 0;
 }