linux-kernel - [PATCH v3 1/3] rcu/exp: Use NMI to get the backtrace of cpu_curr(other

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Date:   Sat, 30 Jul 2022 18:23:28 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        "Mel Gorman" <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        "Josh Triplett" <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, <rcu@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v3 1/3] rcu/exp: Use NMI to get the backtrace of cpu_curr(other_cpu) first

The backtrace of cpu_curr(other_cpu) is unwinded based on the 'fp' saved
during its last switch-out. For the most part, it's out of date. So try
to use NMI to get the backtrace first, just like those functions in
"tree_stall.h" did. Such as rcu_dump_cpu_stacks().

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 kernel/rcu/tree_exp.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 0f70f62039a9090..21381697de23f0b 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -665,7 +665,8 @@ static void synchronize_rcu_expedited_wait(void)
 				mask = leaf_node_cpu_bit(rnp, cpu);
 				if (!(READ_ONCE(rnp->expmask) & mask))
 					continue;
-				dump_cpu_task(cpu);
+				if (!trigger_single_cpu_backtrace(cpu))
+					dump_cpu_task(cpu);
 			}
 		}
 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
-- 
2.25.1