rcu-tasks: Idle tasks on offline CPUs are in quiescent states

Any idle task corresponding to an offline CPU is in an RCU Tasks Trace
quiescent state.  This commit causes rcu_tasks_trace_postscan() to ignore
idle tasks for offline CPUs, which it can do safely due to CPU-hotplug
operations being disabled.

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 8fe78a7..ec68bfe 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1451,7 +1451,7 @@ static void rcu_tasks_trace_postscan(struct list_head *hop)
 {
        int cpu;
 
-       for_each_possible_cpu(cpu)
+       for_each_online_cpu(cpu)
                rcu_tasks_trace_pertask(idle_task(cpu), hop);
 
        // Re-enable CPU hotplug now that the tasklist scan has completed.