linux-kernel - [PATCH rcu 09/13] rcu-tasks: Correct comparisons for CPU numbers in show_stalled_task

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Message-Id: <20210915234604.3907802-9-paulmck@kernel.org>
Date:   Wed, 15 Sep 2021 16:46:00 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 09/13] rcu-tasks: Correct comparisons for CPU numbers in show_stalled_task_trace

From: Neeraj Upadhyay <neeraju@...eaurora.org>

Valid CPU numbers can be zero or greater, but the checks for
->trc_ipi_to_cpu and tick_nohz_full_cpu()'s argument are for strictly
greater than.  This commit therefore corrects the check for no_hz_full
cpu in show_stalled_task_trace() so as to include cpu 0.

Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tasks.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index e2ec548fc0c4..af7388849bed 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1084,9 +1084,9 @@ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
 	cpu = task_cpu(t);
 	pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n",
 		 t->pid,
-		 ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0],
+		 ".I"[READ_ONCE(t->trc_ipi_to_cpu) >= 0],
 		 ".i"[is_idle_task(t)],
-		 ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)],
+		 ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)],
 		 READ_ONCE(t->trc_reader_nesting),
 		 " N"[!!READ_ONCE(t->trc_reader_special.b.need_qs)],
 		 cpu);
-- 
2.31.1.189.g2e36527f23