Commit 81b4a7bc authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu-tasks: Disable CPU hotplug across RCU tasks trace scans 



This commit disables CPU hotplug across RCU tasks trace scans, which
is a first step towards correctly recognizing idle tasks "running" on
offline CPUs.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent b38f57c1

kernel/rcu/tasks.h

+14 −4
Original line number Diff line number Diff line
@@ -910,16 +910,16 @@ static void rcu_tasks_trace_pregp_step(void) 
{

	int cpu;



	// Wait for CPU-hotplug paths to complete.

	cpus_read_lock();

	cpus_read_unlock();



	// Allow for fast-acting IPIs.

	atomic_set(&trc_n_readers_need_end, 1);



	// There shouldn't be any old IPIs, but...

	for_each_possible_cpu(cpu)

		WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu));



	// Disable CPU hotplug across the tasklist scan.

	// This also waits for all readers in CPU-hotplug code paths.

	cpus_read_lock();

}



/* Do first-round processing for the specified task. */
@@ -935,6 +935,9 @@ static void rcu_tasks_trace_pertask(struct task_struct *t, 
/* Do intermediate processing between task and holdout scans. */

static void rcu_tasks_trace_postscan(void)

{

	// Re-enable CPU hotplug now that the tasklist scan has completed.

	cpus_read_unlock();



	// Wait for late-stage exiting tasks to finish exiting.

	// These might have passed the call to exit_tasks_rcu_finish().

	synchronize_rcu();
@@ -979,6 +982,9 @@ static void check_all_holdout_tasks_trace(struct list_head *hop, 
{

	struct task_struct *g, *t;



	// Disable CPU hotplug across the holdout list scan.

	cpus_read_lock();



	list_for_each_entry_safe(t, g, hop, trc_holdout_list) {

		// If safe and needed, try to check the current task.

		if (READ_ONCE(t->trc_ipi_to_cpu) == -1 &&
@@ -991,6 +997,10 @@ static void check_all_holdout_tasks_trace(struct list_head *hop, 
		else if (needreport)

			show_stalled_task_trace(t, firstreport);

	}



	// Re-enable CPU hotplug now that the holdout list scan has completed.

	cpus_read_unlock();



	if (needreport) {

		if (firstreport)

			pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n");