rcu-tasks: RCU Tasks Trace grace-period kthread has implicit QS

Because the task driving the grace-period kthread is in quiescent state
throughout, this commit excludes it from the list of tasks from which
a quiescent state is needed.

This does mean that attaching a sleepable BPF program to function in
kernel/rcu/tasks.h is a bad idea, by the way.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: KP Singh <kpsingh@kernel.org>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 414861d651964576cabaaa7e4279eab4e339132a..554b2e59a1d5a8712de091444a91a58a1b0574fa 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1433,8 +1433,9 @@ 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. Just return.
-       if (unlikely(t == NULL))
+       // 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)
                return;
 
        rcu_st_need_qs(t, 0);