rcu: Create rcutree plugins to handle hotplug CPU for multi-level trees

When offlining CPUs from a multi-level tree, there is the
possibility of offlining the last CPU from a given node when
there are preempted RCU read-side critical sections that
started life on one of the CPUs on that node.

In this case, the corresponding tasks will be enqueued via the
task_struct's rcu_node_entry list_head onto one of the
rcu_node's blocked_tasks[] lists.  These tasks need to be moved
somewhere else so that they will prevent the current grace
period from ending. That somewhere is the root rcu_node.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
LKML-Reference: <20090827215816.GA30472@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 79d4baee31b..9e7f2e8fc66 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -98,7 +98,7 @@ extern struct group_info init_groups;
 #define INIT_TASK_RCU_PREEMPT(tsk)                                      \
         .rcu_read_lock_nesting = 0,                                     \
         .rcu_read_unlock_special = 0,                                   \
-        .rcu_blocked_cpu = -1,                                          \
+        .rcu_blocked_node = NULL,                                       \
         .rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry),
 #else
 #define INIT_TASK_RCU_PREEMPT(tsk)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index bfca26d63b1..3fe03151a8e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1208,7 +1208,7 @@ struct task_struct {
 #ifdef CONFIG_TREE_PREEMPT_RCU
         int rcu_read_lock_nesting;
         char rcu_read_unlock_special;
-        int rcu_blocked_cpu;
+        void *rcu_blocked_node;
         struct list_head rcu_node_entry;
 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 
@@ -1735,7 +1735,7 @@ static inline void rcu_copy_process(struct task_struct *p)
 {
         p->rcu_read_lock_nesting = 0;
         p->rcu_read_unlock_special = 0;
-        p->rcu_blocked_cpu = -1;
+        p->rcu_blocked_node = NULL;
         INIT_LIST_HEAD(&p->rcu_node_entry);
 }