rcu: Make rcu_tasks_kthread()'s GP-wait loop allow preemption
The grace-period-wait loop in rcu_tasks_kthread() is under (unnecessary)
RCU protection, and therefore has no preemption points in a PREEMPT=n
kernel. This commit therefore removes the RCU protection and inserts
cond_resched().
Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 2658de4..f86d1ae 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -467,7 +467,7 @@
(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
ACCESS_ONCE(t->rcu_tasks_holdout) = false;
- list_del_rcu(&t->rcu_tasks_holdout_list);
+ list_del_init(&t->rcu_tasks_holdout_list);
put_task_struct(t);
return;
}
@@ -573,6 +573,7 @@
bool firstreport;
bool needreport;
int rtst;
+ struct task_struct *t1;
schedule_timeout_interruptible(HZ);
rtst = ACCESS_ONCE(rcu_task_stall_timeout);
@@ -582,11 +583,11 @@
lastreport = jiffies;
firstreport = true;
WARN_ON(signal_pending(current));
- rcu_read_lock();
- list_for_each_entry_rcu(t, &rcu_tasks_holdouts,
- rcu_tasks_holdout_list)
+ list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
+ rcu_tasks_holdout_list) {
check_holdout_task(t, needreport, &firstreport);
- rcu_read_unlock();
+ cond_resched();
+ }
}
/*
