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From: "Paul E. McKenney" <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,
	"Jiangong.Han" <jiangong.han@windriver.com>,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 3/7] rcuscale: Console output claims too few grace periods
Date: Wed, 21 Jul 2021 14:04:37 -0700	[thread overview]
Message-ID: <20210721210441.796995-3-paulmck@kernel.org> (raw)
In-Reply-To: <20210721210421.GA788053@paulmck-ThinkPad-P17-Gen-1>

From: "Jiangong.Han" <jiangong.han@windriver.com>

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@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.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 dca51fe9c73f2..2cc34a22a5060 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,
-- 
2.31.1.189.g2e36527f23


  parent reply	other threads:[~2021-07-21 21:04 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-21 21:04 [PATCH rcu 0/7] Torture-test updates for v5.15 Paul E. McKenney
2021-07-21 21:04 ` [PATCH rcu 1/7] refscale: Add measurement of clock readout Paul E. McKenney
2021-07-28 17:38   ` [PATCH v2 " Paul E. McKenney
2021-07-21 21:04 ` [PATCH rcu 2/7] rcutorture: Preempt rather than block when testing task stalls Paul E. McKenney
2021-07-21 21:04 ` Paul E. McKenney [this message]
2021-07-21 21:04 ` [PATCH rcu 4/7] locktorture: Mark statistics data races Paul E. McKenney
2021-07-21 21:04 ` [PATCH rcu 5/7] locktorture: Count lock readers Paul E. McKenney
2021-07-21 21:04 ` [PATCH rcu 6/7] scftorture: Add RPC-like IPI tests Paul E. McKenney
2021-07-21 21:04 ` [PATCH rcu 7/7] scftorture: Avoid NULL pointer exception on early exit Paul E. McKenney

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