rcu: Clear .exp_hint only when deferred quiescent state has been reported (2eeba583) · Commits · 戴 / test

Currently, the .exp_hint flag is cleared in rcu_read_unlock_special(), which works, but which can also prevent subsequent rcu_read_unlock() calls from helping expedite the quiescent state needed by an ongoing expedited RCU grace period. This commit therefore defers clearing of .exp_hint from rcu_read_unlock_special() to rcu_preempt_deferred_qs_irqrestore(), thus ensuring that intervening calls to rcu_read_unlock() have a chance to help end the expedited grace period. Signed-off-by:

Lai Jiangshan <laijs@linux.alibaba.com> Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree_plugin.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -444,6 +444,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
		local_irq_restore(flags);
		return;
		}
		t->rcu_read_unlock_special.b.exp_hint = false;
		t->rcu_read_unlock_special.b.deferred_qs = false;
		if (special.b.need_qs) {
		rcu_qs();
		@@ -610,7 +611,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
		struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
		struct rcu_node *rnp = rdp->mynode;

		t->rcu_read_unlock_special.b.exp_hint = false;
		exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) \|\|
		(rdp->grpmask & rnp->expmask) \|\|
		tick_nohz_full_cpu(rdp->cpu);
		@@ -640,7 +640,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
		local_irq_restore(flags);
		return;
		}
		WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
		rcu_preempt_deferred_qs_irqrestore(t, flags);
		}

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