[PATCH rcu 2/3] rcu-tasks: Ensure RCU Tasks Trace loops have quiescent states

From: Paul E. McKenney
Date: Wed Aug 31 2022 - 14:21:51 EST


The RCU Tasks Trace grace-period kthread loops across all CPUs, and
there can be quite a few CPUs, with some commercially available systems
sporting well over a thousand of them. Some of these loops can feature
IPIs, which can take some time. This commit therefore places a call to
cond_resched_tasks_rcu_qs() in each such loop.

Link: https://docs.google.com/document/d/1V0YnG1HTWMt9WHJjroiJL9lf-hMrud4v8Fn3fhyY0cI/edit?usp=sharing
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/tasks.h | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 469bf2a3b505e..f5bf6fb430dab 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1500,6 +1500,7 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop)
if (rcu_tasks_trace_pertask_prep(t, true))
trc_add_holdout(t, hop);
rcu_read_unlock();
+ cond_resched_tasks_rcu_qs();
}

// Only after all running tasks have been accounted for is it
@@ -1520,6 +1521,7 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop)
raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
}
raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
+ cond_resched_tasks_rcu_qs();
}

// Re-enable CPU hotplug now that the holdout list is populated.
@@ -1619,6 +1621,7 @@ static void check_all_holdout_tasks_trace(struct list_head *hop,
trc_del_holdout(t);
else if (needreport)
show_stalled_task_trace(t, firstreport);
+ cond_resched_tasks_rcu_qs();
}

// Re-enable CPU hotplug now that the holdout list scan has completed.
--
2.31.1.189.g2e36527f23