linux-kernel - [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits with HZ/20

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Date:   Wed, 16 Aug 2023 20:49:12 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>
Cc:     rcu@...r.kernel.org
Subject: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits with HZ/20

In the past, we see that spinning on schedule_timeout* with a wait of 1
jiffie can hang the kernel. See d52d3a2bf408 ("torture: Fix hang during
kthread shutdown phase").

Recently again it showed up in torture's stutter code as well. The behavior is
the the function may instantly return and never go to sleep preempting whatever
was running under it.

To prevent future issues, apply the same fix mentioned in the above
commit d52d3a2bf408 to more places.

I took care to only apply it to places where I thought it made sense.

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/rcutorture.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 8dd52ea78b52..a31297f32a2a 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1153,7 +1153,7 @@ static int rcu_torture_boost(void *arg)
 				mutex_unlock(&boost_mutex);
 				break;
 			}
-			schedule_timeout_uninterruptible(1);
+			schedule_timeout_uninterruptible(HZ / 20);
 		}
 
 		/* Go do the stutter. */
@@ -1164,7 +1164,7 @@ checkwait:	if (stutter_wait("rcu_torture_boost"))
 	/* Clean up and exit. */
 	while (!kthread_should_stop()) {
 		torture_shutdown_absorb("rcu_torture_boost");
-		schedule_timeout_uninterruptible(1);
+		schedule_timeout_uninterruptible(HZ / 20);
 	}
 	torture_kthread_stopping("rcu_torture_boost");
 	return 0;
@@ -1187,7 +1187,7 @@ rcu_torture_fqs(void *arg)
 		fqs_resume_time = jiffies + fqs_stutter * HZ;
 		while (time_before(jiffies, fqs_resume_time) &&
 		       !kthread_should_stop()) {
-			schedule_timeout_interruptible(1);
+			schedule_timeout_interruptible(HZ / 20);
 		}
 		fqs_burst_remaining = fqs_duration;
 		while (fqs_burst_remaining > 0 &&
@@ -2903,7 +2903,7 @@ static int rcu_torture_fwd_prog(void *args)
 			WRITE_ONCE(rcu_fwd_seq, rcu_fwd_seq + 1);
 		} else {
 			while (READ_ONCE(rcu_fwd_seq) == oldseq && !torture_must_stop())
-				schedule_timeout_interruptible(1);
+				schedule_timeout_interruptible(HZ / 20);
 			oldseq = READ_ONCE(rcu_fwd_seq);
 		}
 		pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id);
@@ -3204,7 +3204,7 @@ static int rcu_torture_read_exit_child(void *trsp_in)
 	set_user_nice(current, MAX_NICE);
 	// Minimize time between reading and exiting.
 	while (!kthread_should_stop())
-		schedule_timeout_uninterruptible(1);
+		schedule_timeout_uninterruptible(HZ / 20);
 	(void)rcu_torture_one_read(trsp, -1);
 	return 0;
 }
@@ -3252,7 +3252,7 @@ static int rcu_torture_read_exit(void *unused)
 	smp_mb(); // Store before wakeup.
 	wake_up(&read_exit_wq);
 	while (!torture_must_stop())
-		schedule_timeout_uninterruptible(1);
+		schedule_timeout_uninterruptible(HZ / 20);
 	torture_kthread_stopping("rcu_torture_read_exit");
 	return 0;
 }
-- 
2.41.0.694.ge786442a9b-goog