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From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 3/4] rcu: Do not NMI offline CPUs
Date: Wed,  6 Jan 2021 08:52:30 -0800
Message-ID: <20210106165231.20441-3-paulmck@kernel.org> (raw)
In-Reply-To: <20210106165210.GA20296@paulmck-ThinkPad-P72>

From: "Paul E. McKenney" <paulmck@kernel.org>

Currently, RCU CPU stall warning messages will NMI whatever CPU looks
like it is blocking either the current grace period or the grace-period
kthread.  This can produce confusing output if the target CPU is offline.
This commit therefore checks for offline CPUs.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_stall.h | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 35c1355..29cf096 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -333,9 +333,12 @@ static void rcu_dump_cpu_stacks(void)
 	rcu_for_each_leaf_node(rnp) {
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		for_each_leaf_node_possible_cpu(rnp, cpu)
-			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
-				if (!trigger_single_cpu_backtrace(cpu))
+			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+				if (cpu_is_offline(cpu))
+					pr_err("Offline CPU %d blocking current GP.\n", cpu);
+				else if (!trigger_single_cpu_backtrace(cpu))
 					dump_cpu_task(cpu);
+			}
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
 }
@@ -466,9 +469,13 @@ static void rcu_check_gp_kthread_starvation(void)
 			pr_err("RCU grace-period kthread stack dump:\n");
 			sched_show_task(gpk);
 			if (cpu >= 0) {
-				pr_err("Stack dump where RCU grace-period kthread last ran:\n");
-				if (!trigger_single_cpu_backtrace(cpu))
-					dump_cpu_task(cpu);
+				if (cpu_is_offline(cpu)) {
+					pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
+				} else  {
+					pr_err("Stack dump where RCU GP kthread last ran:\n");
+					if (!trigger_single_cpu_backtrace(cpu))
+						dump_cpu_task(cpu);
+				}
 			}
 			wake_up_process(gpk);
 		}
-- 
2.9.5


  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06 16:52 [PATCH tip/core/rcu 0/4] Stall-warning updates for v5.12 Paul E. McKenney
2021-01-06 16:52 ` [PATCH tip/core/rcu 1/4] rcu: Mark obtuse portion of stall warning as internal debug paulmck
2021-01-06 16:52 ` [PATCH tip/core/rcu 2/4] rcu: For RCU grace-period kthread starvation, dump last CPU it ran on paulmck
2021-01-06 16:52 ` paulmck [this message]
2021-01-06 16:52 ` [PATCH tip/core/rcu 4/4] rcu: Check and report missed fqs timer wakeup on RCU stall paulmck

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