linux-kernel - [PATCH v4 2/2] rcutorture: Correctly compute probability to invoke ->exp

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Message-Id: <20251229191616.693898-2-paulmck@kernel.org>
Date: Mon, 29 Dec 2025 11:16:16 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Chris Mason <clm@...a.com>,
	Joel Fernandes <joelagnelf@...dia.com>
Subject: [PATCH v4 2/2] rcutorture: Correctly compute probability to invoke ->exp_current()

Lack of parentheses causes the ->exp_current() function, for example,
srcu_expedite_current(), to be called only once in four billion times
instead of the intended once in 256 times.  This commit therefore adds
the needed parentheses.

Reported-by: Chris Mason <clm@...a.com>
Reported-by: Joel Fernandes <joelagnelf@...dia.com>
Fixes: 950063c6e897 ("rcutorture: Test srcu_expedite_current()")
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/rcutorture.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 63053031ade21..47ce7f49b52c6 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1749,7 +1749,7 @@ rcu_torture_writer(void *arg)
 					ulo[i] = cur_ops->get_comp_state();
 				gp_snap = cur_ops->start_gp_poll();
 				rcu_torture_writer_state = RTWS_POLL_WAIT;
-				if (cur_ops->exp_current && !torture_random(&rand) % 0xff)
+				if (cur_ops->exp_current && !(torture_random(&rand) & 0xff))
 					cur_ops->exp_current();
 				while (!cur_ops->poll_gp_state(gp_snap)) {
 					gp_snap1 = cur_ops->get_gp_state();
@@ -1771,7 +1771,7 @@ rcu_torture_writer(void *arg)
 					cur_ops->get_comp_state_full(&rgo[i]);
 				cur_ops->start_gp_poll_full(&gp_snap_full);
 				rcu_torture_writer_state = RTWS_POLL_WAIT_FULL;
-				if (cur_ops->exp_current && !torture_random(&rand) % 0xff)
+				if (cur_ops->exp_current && !(torture_random(&rand) & 0xff))
 					cur_ops->exp_current();
 				while (!cur_ops->poll_gp_state_full(&gp_snap_full)) {
 					cur_ops->get_gp_state_full(&gp_snap1_full);
-- 
2.40.1