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

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Message-Id: <20220831181556.2696404-2-paulmck@kernel.org>
Date:   Wed, 31 Aug 2022 11:15:55 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 2/3] rcu-tasks: Ensure RCU Tasks Trace loops have quiescent states

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@...nel.org>
---
 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