rcu: priority boosting for TINY_PREEMPT_RCU

Add priority boosting, but only for TINY_PREEMPT_RCU.  This is enabled
by the default-off RCU_BOOST kernel parameter.  The priority to which to
boost preempted RCU readers is controlled by the RCU_BOOST_PRIO kernel
parameter (defaulting to real-time priority 1) and the time to wait
before boosting the readers blocking a given grace period is controlled
by the RCU_BOOST_DELAY kernel parameter (defaulting to 500 milliseconds).

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e18473f0eb78..ed1a9bc52b2f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1210,6 +1210,9 @@ 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;
@@ -1745,7 +1748,8 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #ifdef CONFIG_PREEMPT_RCU
 
 #define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */
-#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */
+#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. */
 
 static inline void rcu_copy_process(struct task_struct *p)
 {
@@ -1753,7 +1757,10 @@ static inline void rcu_copy_process(struct task_struct *p)
         p->rcu_read_unlock_special = 0;
 #ifdef CONFIG_TREE_PREEMPT_RCU
         p->rcu_blocked_node = NULL;
-#endif
+#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);
 }