linux-kernel - [PATCH v3] rcuscale: Console output claims too few grace periods

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Message-Id: <20210624143424.16158-1-jiangong.han@windriver.com>
Date:   Thu, 24 Jun 2021 22:34:24 +0800
From:   "Jiangong.Han" <jiangong.han@...driver.com>
To:     dave@...olabs.net, paulmck@...nel.org, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, joel@...lfernandes.org
Cc:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        "Jiangong.Han" <jiangong.han@...driver.com>
Subject: [PATCH v3] rcuscale: Console output claims too few grace periods

The rcuscale console output claims N grace periods, numbered from zero
to N, which means that there were really N+1 grace periods.  The root
cause of this bug is that rcu_scale_writer() stores the number of the
last grace period (numbered from zero) into writer_n_durations[me]
instead of the number of grace periods. This commit therefore assigns
the actual number of grace periods to writer_n_durations[me], and also
makes the corresponding adjustment to the loop outputting per-grace-period
measurements.

Sample of old console output:
	rcu-scale: writer 0 gps: 133
	......
	rcu-scale:    0 writer-duration:     0 44003961
	rcu-scale:    0 writer-duration:     1 32003582
	......
	rcu-scale:    0 writer-duration:   132 28004391
	rcu-scale:    0 writer-duration:   133 27996410

Sample of new console output:
	rcu-scale: writer 0 gps: 134
	......
	rcu-scale:    0 writer-duration:     0 44003961
	rcu-scale:    0 writer-duration:     1 32003582
	......
	rcu-scale:    0 writer-duration:   132 28004391
	rcu-scale:    0 writer-duration:   133 27996410

Signed-off-by: Jiangong.Han <jiangong.han@...driver.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/rcuscale.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index dca51fe9c73f..2cc34a22a506 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -487,7 +487,7 @@ rcu_scale_writer(void *arg)
 	if (gp_async) {
 		cur_ops->gp_barrier();
 	}
-	writer_n_durations[me] = i_max;
+	writer_n_durations[me] = i_max + 1;
 	torture_kthread_stopping("rcu_scale_writer");
 	return 0;
 }
@@ -561,7 +561,7 @@ rcu_scale_cleanup(void)
 			wdpp = writer_durations[i];
 			if (!wdpp)
 				continue;
-			for (j = 0; j <= writer_n_durations[i]; j++) {
+			for (j = 0; j < writer_n_durations[i]; j++) {
 				wdp = &wdpp[j];
 				pr_alert("%s%s %4d writer-duration: %5d %llu\n",
 					scale_type, SCALE_FLAG,
-- 
2.17.1