From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> 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@xxxxxxxxxx/ Reported-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx> Reported-by: Yang Jihong <yangjihong1@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Tested-by: Yang Jihong <yangjihong1@xxxxxxxxxx> Tested-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> --- kernel/rcu/tasks.h | 43 +++++++++++++++++++++++++++++++++---------- 1 file changed, 33 insertions(+), 10 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 4a5d562e3189..68a8adf7de8e 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1151,25 +1151,48 @@ 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); } /* -- 2.43.0
