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Date: Tue, 12 May 2015 14:38:09 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
<linux-rt-users@...r.kernel.org>
Subject: [PATCH tip/core/rcu 03/15] rcu: Eliminate a few RCU_BOOST #ifdefs in favor of IS_ENABLED()
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: <linux-rt-users@...r.kernel.org>
---
kernel/rcu/tree.h | 2 --
kernel/rcu/tree_plugin.h | 35 ++++++++++++++++++++---------------
2 files changed, 20 insertions(+), 17 deletions(-)
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index a69d3dab2ec4..dd5ce4034875 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -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. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9a04764dd239..8f8142778684 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -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 (&t->rcu_node_entry == rnp->boost_tasks)
- rnp->boost_tasks = np;
- /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
- drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
-#endif /* #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 w/rnp->lock held. */
+ drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+ }
/*
* 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,
--
1.8.1.5
--
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