linux-kernel - [PATCH tick-sched] Clarify "NOHZ: local_softirq

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Message-ID: <20200626210506.GA27189@paulmck-ThinkPad-P72>
Date:   Fri, 26 Jun 2020 14:05:06 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     fweisbec@...il.com, tglx@...utronix.de, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, luto@...nel.org, kernel-team@...com
Subject: [PATCH tick-sched] Clarify "NOHZ: local_softirq_pending" warning

Currently, can_stop_idle_tick() prints "NOHZ: local_softirq_pending HH"
(where "HH" is the hexadecimal softirq vector number) when one or more
non-RCU softirq handlers are still enablded when checking to stop the
scheduler-tick interrupt.  This message is not as enlightening as one
might hope, so this commit changes it to "NOHZ tick-stop error: Non-RCU
local softirq work is pending, handler #HH.

Reported-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

---

 tick-sched.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f0199a4..349a25a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -927,7 +927,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)

 		if (ratelimit < 10 &&
 		    (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
-			pr_warn("NOHZ: local_softirq_pending %02x\n",
+			pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x\n",
 				(unsigned int) local_softirq_pending());
 			ratelimit++;
 		}