From 19415004d5221ba59be6ef566fdbb52c44808f7e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 17 May 2022 17:38:02 -0700 Subject: [PATCH] rcu-tasks: Avoid rcu_tasks_trace_pertask() duplicate list additions This commit adds checks within rcu_tasks_trace_pertask() to avoid duplicate (and destructive) additions to the holdouts list. These checks will be required later due to the possibility of a given task having blocked while in an RCU Tasks Trace read-side critical section, but now running on a CPU. Signed-off-by: Paul E. McKenney Cc: Neeraj Upadhyay Cc: Eric Dumazet Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: Martin KaFai Lau Cc: KP Singh --- kernel/rcu/tasks.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 66d8473f1bda1..1aa6a24a9bc2b 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1454,9 +1454,10 @@ static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop) { // During early boot when there is only the one boot CPU, there - // is no idle task for the other CPUs. Also, the grace-period - // kthread is always in a quiescent state. Either way, just return. - if (unlikely(t == NULL) || t == current) + // is no idle task for the other CPUs. Also, the grace-period + // kthread is always in a quiescent state. In addition, just return + // if this task is already on the list. + if (unlikely(t == NULL) || t == current || !list_empty(&t->trc_holdout_list)) return; rcu_st_need_qs(t, 0); -- 2.30.2