Commit e2f63836 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Add size-state transitioning code 



This is just dead code at the moment, and will be used once
the state-transition code is activated.

Because srcu_barrier() must be aware of transition before call_srcu(), the
state machine waits for an SRCU grace period before callbacks are queued
to the non-CPU-0 queues.  This requres that portions of srcu_barrier()
be enclosed in an SRCU read-side critical section.

Co-developed-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 2ec30311

kernel/rcu/srcutree.c

+13 −0
Original line number Diff line number Diff line
@@ -562,6 +562,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) 
	unsigned long mask;

	struct srcu_data *sdp;

	struct srcu_node *snp;

	int ss_state;



	/* Prevent more than one additional grace period. */

	mutex_lock(&ssp->srcu_cb_mutex);
@@ -629,6 +630,15 @@ static void srcu_gp_end(struct srcu_struct *ssp) 
	} else {

		spin_unlock_irq_rcu_node(ssp);

	}



	/* Transition to big if needed. */

	ss_state = smp_load_acquire(&ssp->srcu_size_state);

	if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {

		if (ss_state == SRCU_SIZE_ALLOC)

			init_srcu_struct_nodes(ssp);

		else

			smp_store_release(&ssp->srcu_size_state, ss_state + 1);

	}

}



/*
@@ -1178,6 +1188,7 @@ static void srcu_barrier_one_cpu(struct srcu_struct *ssp, struct srcu_data *sdp) 
void srcu_barrier(struct srcu_struct *ssp)

{

	int cpu;

	int idx;

	unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq);



	check_init_srcu_struct(ssp);
@@ -1193,11 +1204,13 @@ void srcu_barrier(struct srcu_struct *ssp) 
	/* Initial count prevents reaching zero until all CBs are posted. */

	atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);



	idx = srcu_read_lock(ssp);

	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)

		srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));

	else

		for_each_possible_cpu(cpu)

			srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));

	srcu_read_unlock(ssp, idx);



	/* Remove the initial count, at which point reaching zero can happen. */

	if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))