[PATCH rcu 10/32] rcu-tasks: RCU Tasks Trace grace-period kthread has implicit QS

Paul E. McKenney
2022-06-20T22:54:56Z

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>
---
kernel/rcu/tasks.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 414861d651964..554b2e59a1d5a 100644
--- 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);
--
2.31.1.189.g2e36527f23