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Commit 4de376a1 authored by Pranith Kumar's avatar Pranith Kumar Committed by Paul E. McKenney
Browse files

rcu: Remove remaining read-modify-write ACCESS_ONCE() calls 



Change the remaining uses of ACCESS_ONCE() so that each ACCESS_ONCE() either does a load or a store, but not both.

Signed-off-by: default avatarPranith Kumar <bobby.prani@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 11ed7f93

kernel/rcu/tree.c

+4 −2
Original line number Diff line number Diff line
@@ -1684,7 +1684,8 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in) 
	if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {

		raw_spin_lock_irq(&rnp->lock);

		smp_mb__after_unlock_lock();

		ACCESS_ONCE(rsp->gp_flags) &= ~RCU_GP_FLAG_FQS;

		ACCESS_ONCE(rsp->gp_flags) =

			ACCESS_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS;

		raw_spin_unlock_irq(&rnp->lock);

	}

	return fqs_state;
@@ -2505,7 +2506,8 @@ static void force_quiescent_state(struct rcu_state *rsp) 
		raw_spin_unlock_irqrestore(&rnp_old->lock, flags);

		return;  /* Someone beat us to it. */

	}

	ACCESS_ONCE(rsp->gp_flags) |= RCU_GP_FLAG_FQS;

	ACCESS_ONCE(rsp->gp_flags) =

		ACCESS_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS;

	raw_spin_unlock_irqrestore(&rnp_old->lock, flags);

	wake_up(&rsp->gp_wq);  /* Memory barrier implied by wake_up() path. */

}

kernel/rcu/tree_plugin.h

+5 −3
Original line number Diff line number Diff line
@@ -897,7 +897,8 @@ void synchronize_rcu_expedited(void) 


	/* Clean up and exit. */

	smp_mb(); /* ensure expedited GP seen before counter increment. */

	ACCESS_ONCE(sync_rcu_preempt_exp_count)++;

	ACCESS_ONCE(sync_rcu_preempt_exp_count) =

					sync_rcu_preempt_exp_count + 1;

unlock_mb_ret:

	mutex_unlock(&sync_rcu_preempt_exp_mutex);

mb_ret:
@@ -2428,8 +2429,9 @@ static int rcu_nocb_kthread(void *arg) 
			list = next;

		}

		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);

		ACCESS_ONCE(rdp->nocb_p_count) -= c;

		ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;

		ACCESS_ONCE(rdp->nocb_p_count) = rdp->nocb_p_count - c;

		ACCESS_ONCE(rdp->nocb_p_count_lazy) =

						rdp->nocb_p_count_lazy - cl;

		rdp->n_nocbs_invoked += c;

	}

	return 0;