rcu: Simplify priority boosting by putting rt_mutex in rcu_node
RCU priority boosting currently checks for boosting via a pointer in
task_struct. However, this is not needed: As Oleg noted, if the
rt_mutex is placed in the rcu_node instead of on the booster's stack,
the boostee can simply check it see if it owns the lock. This commit
makes this change, shrinking task_struct by one pointer and the kernel
by thirteen lines.
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6df7f9f..2bb4c4f3 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -102,12 +102,6 @@
#define INIT_IDS
#endif
-#ifdef CONFIG_RCU_BOOST
-#define INIT_TASK_RCU_BOOST() \
- .rcu_boost_mutex = NULL,
-#else
-#define INIT_TASK_RCU_BOOST()
-#endif
#ifdef CONFIG_TREE_PREEMPT_RCU
#define INIT_TASK_RCU_TREE_PREEMPT() \
.rcu_blocked_node = NULL,
@@ -119,8 +113,7 @@
.rcu_read_lock_nesting = 0, \
.rcu_read_unlock_special = 0, \
.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \
- INIT_TASK_RCU_TREE_PREEMPT() \
- INIT_TASK_RCU_BOOST()
+ INIT_TASK_RCU_TREE_PREEMPT()
#else
#define INIT_TASK_RCU_PREEMPT(tsk)
#endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 306f4f0..3cfbc05 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1270,9 +1270,6 @@
#ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_node *rcu_blocked_node;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-#ifdef CONFIG_RCU_BOOST
- struct rt_mutex *rcu_boost_mutex;
-#endif /* #ifdef CONFIG_RCU_BOOST */
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
struct sched_info sched_info;
@@ -2009,9 +2006,6 @@
#ifdef CONFIG_TREE_PREEMPT_RCU
p->rcu_blocked_node = NULL;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-#ifdef CONFIG_RCU_BOOST
- p->rcu_boost_mutex = NULL;
-#endif /* #ifdef CONFIG_RCU_BOOST */
INIT_LIST_HEAD(&p->rcu_node_entry);
}