EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
/**
---- -- * cond_synchronize_rcu - Conditionally wait for an RCU grace period
++++ ++ * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed?
++++ ++ * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
+ *
++++ ++ * If a full RCU grace period has elapsed since the earlier call from
++++ ++ * which *rgosp was obtained, return @true, otherwise return @false.
++++ ++ * If @false is returned, it is the caller's responsibility to invoke this
++++ ++ * function later on until it does return @true. Alternatively, the caller
++++ ++ * can explicitly wait for a grace period, for example, by passing @rgosp
++++ ++ * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
++++ ++ *
++++ ++ * Yes, this function does not take counter wrap into account.
++++ ++ * But counter wrap is harmless. If the counter wraps, we have waited
++++ ++ * for more than a billion grace periods (and way more on a 64-bit
++++ ++ * system!). Those needing to keep rcu_gp_oldstate values for very
++++ ++ * long time periods (many hours even on 32-bit systems) should check
++++ ++ * them occasionally and either refresh them or set a flag indicating
++++ ++ * that the grace period has completed. Alternatively, they can use
++++ ++ * get_completed_synchronize_rcu_full() to get a guaranteed-completed
++++ ++ * grace-period state.
++ + ++ *
++++ ++ * This function provides the same memory-ordering guarantees that would
++++ ++ * be provided by a synchronize_rcu() that was invoked at the call to
++++ ++ * the function that provided @rgosp, and that returned at the end of this
++++ ++ * function. And this guarantee requires that the root rcu_node structure's
++++ ++ * ->gp_seq field be checked instead of that of the rcu_state structure.
++++ ++ * The problem is that the just-ending grace-period's callbacks can be
++++ ++ * invoked between the time that the root rcu_node structure's ->gp_seq
++++ ++ * field is updated and the time that the rcu_state structure's ->gp_seq
++++ ++ * field is updated. Therefore, if a single synchronize_rcu() is to
++++ ++ * cause a subsequent poll_state_synchronize_rcu_full() to return @true,
++++ ++ * then the root rcu_node structure is the one that needs to be polled.
++++ ++ */
++++ ++bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
++++ ++{
++++ ++ struct rcu_node *rnp = rcu_get_root();
++++ ++
++++ ++ smp_mb(); // Order against root rcu_node structure grace-period cleanup.
++++ ++ if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED ||
++++ ++ rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) ||
++++ ++ rgosp->rgos_exp == RCU_GET_STATE_COMPLETED ||
++++ ++ rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) {
++++ ++ smp_mb(); /* Ensure GP ends before subsequent accesses. */
++++ ++ return true;
++++ ++ }
++++ ++ return false;
++++ ++}
++++ ++EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
++++ ++
++++ ++/**
++++ ++ * cond_synchronize_rcu - Conditionally wait for an RCU grace period
* @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
*
* If a full RCU grace period has elapsed since the earlier call to