Commit 4aa6e94c authored by Joel Fernandes's avatar Joel Fernandes
Browse files

rcu: Add warning to ensure rcu_seq_done_exact() is working 



The previous patch improved the rcu_seq_done_exact() function by adding
a meaningful constant for the guardband.

Ensure that this is working for the future by a quick check during
rcu_gp_init().

Reviewed-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarJoel Fernandes <joelagnelf@nvidia.com>
parent 9c94c5ad

kernel/rcu/tree.c

+6 −0
Original line number Diff line number Diff line
@@ -1798,6 +1798,7 @@ static noinline_for_stack bool rcu_gp_init(void) 
	struct rcu_data *rdp;

	struct rcu_node *rnp = rcu_get_root();

	bool start_new_poll;

	unsigned long old_gp_seq;



	WRITE_ONCE(rcu_state.gp_activity, jiffies);

	raw_spin_lock_irq_rcu_node(rnp);
@@ -1825,7 +1826,12 @@ static noinline_for_stack bool rcu_gp_init(void) 
	 */

	start_new_poll = rcu_sr_normal_gp_init();

	/* Record GP times before starting GP, hence rcu_seq_start(). */

	old_gp_seq = rcu_state.gp_seq;

	rcu_seq_start(&rcu_state.gp_seq);

	/* Ensure that rcu_seq_done_exact() guardband doesn't give false positives. */

	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&

		     rcu_seq_done_exact(&old_gp_seq, rcu_seq_snap(&rcu_state.gp_seq)));



	ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);

	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));

	rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);