Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3660c281 authored Dec 03, 2013 by Paul E. McKenney

rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses



The ->n_force_qs_lh field is accessed without the benefit of any
synchronization, so this commit adds the needed ACCESS_ONCE() wrappers.
Yes, increments to ->n_force_qs_lh can be lost, but contention should
be low and the field is strictly statistical in nature, so this is not
a problem.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

parent 6d0abeca

kernel/rcu/tree.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2304,7 +2304,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
		if (rnp_old != NULL)
		raw_spin_unlock(&rnp_old->fqslock);
		if (ret) {
		rsp->n_force_qs_lh++;
		ACCESS_ONCE(rsp->n_force_qs_lh)++;
		return;
		}
		rnp_old = rnp;
		@@ -2316,7 +2316,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
		smp_mb__after_unlock_lock();
		raw_spin_unlock(&rnp_old->fqslock);
		if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
		rsp->n_force_qs_lh++;
		ACCESS_ONCE(rsp->n_force_qs_lh)++;
		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
		return; /* Someone beat us to it. */
		}

kernel/rcu/tree_trace.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -273,7 +273,7 @@ static void print_one_rcu_state(struct seq_file m, struct rcu_state rsp)
		seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
		rsp->n_force_qs, rsp->n_force_qs_ngp,
		rsp->n_force_qs - rsp->n_force_qs_ngp,
		rsp->n_force_qs_lh, rsp->qlen_lazy, rsp->qlen);
		ACCESS_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
		for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
		if (rnp->level != level) {
		seq_puts(m, "\n");