rcu: Make TASKS_RCU handle nohz_full= CPUs

Currently TASKS_RCU would ignore a CPU running a task in nohz_full=
usermode execution.  There would be neither a context switch nor a
scheduling-clock interrupt to tell TASKS_RCU that the task in question
had passed through a quiescent state.  The grace period would therefore
extend indefinitely.  This commit therefore makes RCU's dyntick-idle
subsystem record the task_struct structure of the task that is running
in dyntick-idle mode on each CPU.  The TASKS_RCU grace period can
then access this information and record a quiescent state on
behalf of any CPU running in dyntick-idle usermode.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index eaacac4ae77d..ec8b34722bcc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1274,6 +1274,7 @@ struct task_struct {
         unsigned long rcu_tasks_nvcsw;
         bool rcu_tasks_holdout;
         struct list_head rcu_tasks_holdout_list;
+        int rcu_tasks_idle_cpu;
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
@@ -2020,6 +2021,7 @@ static inline void rcu_copy_process(struct task_struct *p)
 #ifdef CONFIG_TASKS_RCU
         p->rcu_tasks_holdout = false;
         INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
+        p->rcu_tasks_idle_cpu = -1;
 #endif /* #ifdef CONFIG_TASKS_RCU */
 }