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Commit 8f20a5e8 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 176f8f7a

kernel/rcu/update.c

+6 −5
Original line number Original line Diff line number Diff line
@@ -467,7 +467,7 @@ static void check_holdout_task(struct task_struct *t, 
	    (IS_ENABLED(CONFIG_NO_HZ_FULL) &&

	    (IS_ENABLED(CONFIG_NO_HZ_FULL) &&

	     !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {

	     !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {

		ACCESS_ONCE(t->rcu_tasks_holdout) = false;

		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);

		put_task_struct(t);

		return;

		return;

	}

	}
@@ -573,6 +573,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) 
			bool firstreport;

			bool firstreport;

			bool needreport;

			bool needreport;

			int rtst;

			int rtst;

			struct task_struct *t1;





			schedule_timeout_interruptible(HZ);

			schedule_timeout_interruptible(HZ);

			rtst = ACCESS_ONCE(rcu_task_stall_timeout);

			rtst = ACCESS_ONCE(rcu_task_stall_timeout);
@@ -582,11 +583,11 @@ static int __noreturn rcu_tasks_kthread(void *arg) 
				lastreport = jiffies;

				lastreport = jiffies;

			firstreport = true;

			firstreport = true;

			WARN_ON(signal_pending(current));

			WARN_ON(signal_pending(current));

			rcu_read_lock();

			list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,

			list_for_each_entry_rcu(t, &rcu_tasks_holdouts,

						rcu_tasks_holdout_list) {

						rcu_tasks_holdout_list)

				check_holdout_task(t, needreport, &firstreport);

				check_holdout_task(t, needreport, &firstreport);

			rcu_read_unlock();

				cond_resched();

			}

		}

		}





		/*

		/*