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Commit 82e78d80 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

rcu: Simplify unboosting checks 



Commit 7765be (Fix RCU_BOOST race handling current->rcu_read_unlock_special)
introduced a new ->rcu_boosted field in the task structure.  This is
redundant because the existing ->rcu_boost_mutex will be non-NULL at
any time that ->rcu_boosted is nonzero.  Therefore, this commit removes
->rcu_boosted and tests ->rcu_boost_mutex instead.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 5c51dd73

include/linux/sched.h

+0 −3
Original line number Diff line number Diff line
@@ -1259,9 +1259,6 @@ struct task_struct { 
#ifdef CONFIG_PREEMPT_RCU

	int rcu_read_lock_nesting;

	char rcu_read_unlock_special;

#if defined(CONFIG_RCU_BOOST) && defined(CONFIG_TREE_PREEMPT_RCU)

	int rcu_boosted;

#endif /* #if defined(CONFIG_RCU_BOOST) && defined(CONFIG_TREE_PREEMPT_RCU) */

	struct list_head rcu_node_entry;

#endif /* #ifdef CONFIG_PREEMPT_RCU */

#ifdef CONFIG_TREE_PREEMPT_RCU

kernel/rcutree_plugin.h

+10 −10
Original line number Diff line number Diff line
@@ -306,6 +306,9 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 
	int empty_exp;

	unsigned long flags;

	struct list_head *np;

#ifdef CONFIG_RCU_BOOST

	struct rt_mutex *rbmp = NULL;

#endif /* #ifdef CONFIG_RCU_BOOST */

	struct rcu_node *rnp;

	int special;
@@ -351,6 +354,7 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 
		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */

		np = rcu_next_node_entry(t, rnp);

		list_del_init(&t->rcu_node_entry);

		t->rcu_blocked_node = NULL;

		trace_rcu_unlock_preempted_task("rcu_preempt",

						rnp->gpnum, t->pid);

		if (&t->rcu_node_entry == rnp->gp_tasks)
@@ -360,13 +364,12 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 
#ifdef CONFIG_RCU_BOOST

		if (&t->rcu_node_entry == rnp->boost_tasks)

			rnp->boost_tasks = np;

		/* Snapshot and clear ->rcu_boosted with rcu_node lock held. */

		if (t->rcu_boosted) {

			special |= RCU_READ_UNLOCK_BOOSTED;

			t->rcu_boosted = 0;

		/* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */

		if (t->rcu_boost_mutex) {

			rbmp = t->rcu_boost_mutex;

			t->rcu_boost_mutex = NULL;

		}

#endif /* #ifdef CONFIG_RCU_BOOST */

		t->rcu_blocked_node = NULL;



		/*

		 * If this was the last task on the current list, and if
@@ -387,10 +390,8 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) 


#ifdef CONFIG_RCU_BOOST

		/* Unboost if we were boosted. */

		if (special & RCU_READ_UNLOCK_BOOSTED) {

			rt_mutex_unlock(t->rcu_boost_mutex);

			t->rcu_boost_mutex = NULL;

		}

		if (rbmp)

			rt_mutex_unlock(rbmp);

#endif /* #ifdef CONFIG_RCU_BOOST */



		/*
@@ -1206,7 +1207,6 @@ static int rcu_boost(struct rcu_node *rnp) 
	t = container_of(tb, struct task_struct, rcu_node_entry);

	rt_mutex_init_proxy_locked(&mtx, t);

	t->rcu_boost_mutex = &mtx;

	t->rcu_boosted = 1;

	raw_spin_unlock_irqrestore(&rnp->lock, flags);

	rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */

	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */