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From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     linux-kernel@vger.kernel.org
Cc:     mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.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,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 09/17] rcutorture: Vary forward-progress test interval
Date:   Wed, 29 Aug 2018 14:47:42 -0700
In-Reply-To: <20180829214722.GA23411@linux.vnet.ibm.com>
References: <20180829214722.GA23411@linux.vnet.ibm.com>
Message-Id: <20180829214750.26972-9-paulmck@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Some of the Linux kernel's RCU implementations provide several mechanisms
to promote forward progress that operate over different timeframes.
This commit therefore causes rcu_torture_fwd_prog() to vary the duration
of its forward-progress testing in order to test each such mechanism.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcutorture.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 8ab23143c244..89cc4d9c9a0c 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1676,16 +1676,21 @@ static int rcu_torture_fwd_prog(void *args)
 	unsigned long cver;
 	unsigned long gps;
 	int idx;
+	int sd;
+	int sd4;
 	unsigned long stopat;
 	bool tested = false;
 	int tested_tries = 0;
+	static DEFINE_TORTURE_RANDOM(trs);
 
 	VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");
 	do {
 		schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
 		cver = READ_ONCE(rcu_torture_current_version);
 		gps = cur_ops->get_gp_seq();
-		stopat = jiffies + cur_ops->stall_dur() / fwd_progress_div;
+		sd = cur_ops->stall_dur() + 1;
+		sd4 = (sd + fwd_progress_div - 1) / fwd_progress_div;
+		stopat = jiffies + sd4 + torture_random(&trs) % (sd - sd4);
 		while (time_before(jiffies, stopat) && !torture_must_stop()) {
 			idx = cur_ops->readlock();
 			udelay(10);
-- 
2.17.1