Commit 6b70399f authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Boqun Feng
Browse files

rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks 

This commit continues the elimination of deadlocks involving do_exit()
and RCU tasks by causing exit_tasks_rcu_start() to add the current
task to a per-CPU list and causing exit_tasks_rcu_stop() to remove the
current task from whatever list it is on.  These lists will be used to
track tasks that are exiting, while still accounting for any RCU-tasks
quiescent states that these tasks pass though.

[ paulmck: Apply Frederic Weisbecker feedback. ]

Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/



Reported-by: default avatarChen Zhongjin <chenzhongjin@huawei.com>
Reported-by: default avatarYang Jihong <yangjihong1@huawei.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Tested-by: default avatarYang Jihong <yangjihong1@huawei.com>
Tested-by: default avatarChen Zhongjin <chenzhongjin@huawei.com>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
parent 46faf9d8

kernel/rcu/tasks.h

+33 −10
Original line number Diff line number Diff line
@@ -1147,25 +1147,48 @@ struct task_struct *get_rcu_tasks_gp_kthread(void) 
EXPORT_SYMBOL_GPL(get_rcu_tasks_gp_kthread);



/*

 * Contribute to protect against tasklist scan blind spot while the

 * task is exiting and may be removed from the tasklist. See

 * corresponding synchronize_srcu() for further details.

 * Protect against tasklist scan blind spot while the task is exiting and

 * may be removed from the tasklist.  Do this by adding the task to yet

 * another list.

 *

 * Note that the task will remove itself from this list, so there is no

 * need for get_task_struct(), except in the case where rcu_tasks_pertask()

 * adds it to the holdout list, in which case rcu_tasks_pertask() supplies

 * the needed get_task_struct().

 */

void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)

void exit_tasks_rcu_start(void)

{

	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);

	unsigned long flags;

	struct rcu_tasks_percpu *rtpcp;

	struct task_struct *t = current;



	WARN_ON_ONCE(!list_empty(&t->rcu_tasks_exit_list));

	preempt_disable();

	rtpcp = this_cpu_ptr(rcu_tasks.rtpcpu);

	t->rcu_tasks_exit_cpu = smp_processor_id();

	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);

	if (!rtpcp->rtp_exit_list.next)

		INIT_LIST_HEAD(&rtpcp->rtp_exit_list);

	list_add(&t->rcu_tasks_exit_list, &rtpcp->rtp_exit_list);

	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);

	preempt_enable();

}



/*

 * Contribute to protect against tasklist scan blind spot while the

 * task is exiting and may be removed from the tasklist. See

 * corresponding synchronize_srcu() for further details.

 * Remove the task from the "yet another list" because do_exit() is now

 * non-preemptible, allowing synchronize_rcu() to wait beyond this point.

 */

void exit_tasks_rcu_stop(void) __releases(&tasks_rcu_exit_srcu)

void exit_tasks_rcu_stop(void)

{

	unsigned long flags;

	struct rcu_tasks_percpu *rtpcp;

	struct task_struct *t = current;



	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);

	WARN_ON_ONCE(list_empty(&t->rcu_tasks_exit_list));

	rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, t->rcu_tasks_exit_cpu);

	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);

	list_del_init(&t->rcu_tasks_exit_list);

	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);

}



/*