rcu: Adjust read-side accessor comments for READ_ONCE()

Now that READ_ONCE() implies smp_read_barrier_depends(), the commit
updates now-misleading comments to account for this change.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/rcupdate.h

@@ -433,12 +433,12 @@ static inline void rcu_preempt_sleep_check(void) { }
  * @p: The pointer to read
  *
  * Return the value of the specified RCU-protected pointer, but omit the
- * smp_read_barrier_depends() and keep the READ_ONCE().  This is useful
- * when the value of this pointer is accessed, but the pointer is not
- * dereferenced, for example, when testing an RCU-protected pointer against
- * NULL.  Although rcu_access_pointer() may also be used in cases where
- * update-side locks prevent the value of the pointer from changing, you
- * should instead use rcu_dereference_protected() for this use case.
+ * lockdep checks for being in an RCU read-side critical section.  This is
+ * useful when the value of this pointer is accessed, but the pointer is
+ * not dereferenced, for example, when testing an RCU-protected pointer
+ * against NULL.  Although rcu_access_pointer() may also be used in cases
+ * where update-side locks prevent the value of the pointer from changing,
+ * you should instead use rcu_dereference_protected() for this use case.
  *
  * It is also permissible to use rcu_access_pointer() when read-side
  * access to the pointer was removed at least one grace period ago, as
@@ -521,12 +521,11 @@ static inline void rcu_preempt_sleep_check(void) { }
  * @c: The conditions under which the dereference will take place
  *
  * Return the value of the specified RCU-protected pointer, but omit
- * both the smp_read_barrier_depends() and the READ_ONCE().  This
- * is useful in cases where update-side locks prevent the value of the
- * pointer from changing.  Please note that this primitive does *not*
- * prevent the compiler from repeating this reference or combining it
- * with other references, so it should not be used without protection
- * of appropriate locks.
+ * the READ_ONCE().  This is useful in cases where update-side locks
+ * prevent the value of the pointer from changing.  Please note that this
+ * primitive does *not* prevent the compiler from repeating this reference
+ * or combining it with other references, so it should not be used without
+ * protection of appropriate locks.
  *
  * This function is only for update-side use.  Using this function
  * when protected only by rcu_read_lock() will result in infrequent