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>

1 files changed, 1 insertions, 8 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6df7f9fe0d01..2bb4c4f3531a 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -102,12 +102,6 @@ extern struct group_info init_groups;
 #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 @@ extern struct group_info init_groups;
         .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