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

commit 5c9a9ca44fda41c5e82f50efced5297a9c19760d upstream.

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>
Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index bede3a4f108e328267a759a8e535b6f8ea6dbfdd..ea45a2d53a99e52a05c7f84be0205cf0ba5b848e 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1007,7 +1007,7 @@ 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.