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Commit 727b705b authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Eliminate a few RCU_BOOST #ifdefs in favor of IS_ENABLED() 



This commit removes a few RCU_BOOST #ifdefs, replacing them with
IS_ENABLED()-protected return statements.  This relies on the
optimizer to remove any resulting dead code.  There are several other
RCU_BOOST #ifdefs, however these rely on some per-CPU variables that
are available only under RCU_BOOST.  These might be converted later,
if the simplification proves to outweigh the increase in memory footprint.
One hoped-for advantage is more easily locating compiler errors in
obscure combinations of Kconfig parameters.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: <linux-rt-users@vger.kernel.org>
parent e63c887c

kernel/rcu/tree.h

+0 −2
Original line number Diff line number Diff line
@@ -170,7 +170,6 @@ struct rcu_node { 
				/*  if there is no such task.  If there */

				/*  is no current expedited grace period, */

				/*  then there can cannot be any such task. */

#ifdef CONFIG_RCU_BOOST

	struct list_head *boost_tasks;

				/* Pointer to first task that needs to be */

				/*  priority boosted, or NULL if no priority */
@@ -208,7 +207,6 @@ struct rcu_node { 
	unsigned long n_balk_nos;

				/* Refused to boost: not sure why, though. */

				/*  This can happen due to race conditions. */

#endif /* #ifdef CONFIG_RCU_BOOST */

#ifdef CONFIG_RCU_NOCB_CPU

	wait_queue_head_t nocb_gp_wq[2];

				/* Place for rcu_nocb_kthread() to wait GP. */

kernel/rcu/tree_plugin.h

+20 −15
Original line number Diff line number Diff line
@@ -43,7 +43,17 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); 
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);

DEFINE_PER_CPU(char, rcu_cpu_has_work);



#endif /* #ifdef CONFIG_RCU_BOOST */

#else /* #ifdef CONFIG_RCU_BOOST */



/*

 * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,

 * all uses are in dead code.  Provide a definition to keep the compiler

 * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.

 * This probably needs to be excluded from -rt builds.

 */

#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })



#endif /* #else #ifdef CONFIG_RCU_BOOST */



#ifdef CONFIG_RCU_NOCB_CPU

static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
@@ -180,10 +190,9 @@ static void rcu_preempt_note_context_switch(void) 
		if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {

			list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);

			rnp->gp_tasks = &t->rcu_node_entry;

#ifdef CONFIG_RCU_BOOST

			if (rnp->boost_tasks != NULL)

			if (IS_ENABLED(CONFIG_RCU_BOOST) &&

			    rnp->boost_tasks != NULL)

				rnp->boost_tasks = rnp->gp_tasks;

#endif /* #ifdef CONFIG_RCU_BOOST */

		} else {

			list_add(&t->rcu_node_entry, &rnp->blkd_tasks);

			if (rnp->qsmask & rdp->grpmask)
@@ -263,9 +272,7 @@ void rcu_read_unlock_special(struct task_struct *t) 
	bool empty_exp_now;

	unsigned long flags;

	struct list_head *np;

#ifdef CONFIG_RCU_BOOST

	bool drop_boost_mutex = false;

#endif /* #ifdef CONFIG_RCU_BOOST */

	struct rcu_node *rnp;

	union rcu_special special;
@@ -331,12 +338,12 @@ void rcu_read_unlock_special(struct task_struct *t) 
			rnp->gp_tasks = np;

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

			rnp->exp_tasks = np;

#ifdef CONFIG_RCU_BOOST

		if (IS_ENABLED(CONFIG_RCU_BOOST)) {

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

				rnp->boost_tasks = np;

		/* Snapshot ->boost_mtx ownership with rcu_node lock held. */

			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */

			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;

#endif /* #ifdef CONFIG_RCU_BOOST */

		}



		/*

		 * If this was the last task on the current list, and if
@@ -358,11 +365,9 @@ void rcu_read_unlock_special(struct task_struct *t) 
			raw_spin_unlock_irqrestore(&rnp->lock, flags);

		}



#ifdef CONFIG_RCU_BOOST

		/* Unboost if we were boosted. */

		if (drop_boost_mutex)

		if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)

			rt_mutex_unlock(&rnp->boost_mtx);

#endif /* #ifdef CONFIG_RCU_BOOST */



		/*

		 * If this was the last task on the expedited lists,