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Subject[PATCH RFC tip/core/rcu 22/41] rcu: Simplify unboosting checks
Date
From: "Paul E. McKenney" <paul.mckenney@linaro.org>

This is a port of commit #82e78d80 from TREE_PREEMPT_RCU to
TINY_PREEMPT_RCU.

This commit uses the fact that current->rcu_boost_mutex is set
any time that the RCU_READ_UNLOCK_BOOSTED flag is set in the
current->rcu_read_unlock_special bitmask. This allows tests of
the bit to be changed to tests of the pointer, which in turn allows
the RCU_READ_UNLOCK_BOOSTED flag to be eliminated.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/sched.h | 3 +--
kernel/rcutiny_plugin.h | 10 ++++++----
2 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4032ec1..1db119f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1864,8 +1864,7 @@ extern void task_clear_jobctl_pending(struct task_struct *task,
#ifdef CONFIG_PREEMPT_RCU

#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */
-#define RCU_READ_UNLOCK_BOOSTED (1 << 1) /* boosted while in RCU read-side. */
-#define RCU_READ_UNLOCK_NEED_QS (1 << 2) /* RCU core needs CPU response. */
+#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */

static inline void rcu_copy_process(struct task_struct *p)
{
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 9d7d985..01eac49 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -318,7 +318,6 @@ static int rcu_boost(void)
t = container_of(tb, struct task_struct, rcu_node_entry);
rt_mutex_init_proxy_locked(&mtx, t);
t->rcu_boost_mutex = &mtx;
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
raw_local_irq_restore(flags);
rt_mutex_lock(&mtx);
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
@@ -550,6 +549,9 @@ 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 */
int special;

/*
@@ -615,10 +617,10 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
}
#ifdef CONFIG_RCU_BOOST
/* Unboost self if was boosted. */
- if (special & RCU_READ_UNLOCK_BOOSTED) {
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
- rt_mutex_unlock(t->rcu_boost_mutex);
+ if (t->rcu_boost_mutex != NULL) {
+ rbmp = t->rcu_boost_mutex;
t->rcu_boost_mutex = NULL;
+ rt_mutex_unlock(rbmp);
}
#endif /* #ifdef CONFIG_RCU_BOOST */
local_irq_restore(flags);
--
1.7.8


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