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rcu: Simplify priority boosting by putting rt_mutex in rcu_node

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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>
This commit is contained in:
Paul E. McKenney 2014-06-12 13:30:25 -07:00
commit abaa93d9e1
4 changed files with 15 additions and 28 deletions
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6
include/linux/sched.h
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@ -1270,9 +1270,6 @@ struct task_struct {
#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 @@ static inline void rcu_copy_process(struct task_struct *p)
#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);
}