[PATCH v2 1/2] rcutorture: Update rcutorture_one_extend_check() for lazy preemption

[Boqun Feng <boqun.feng@gmail.com>]

From: "Paul E. McKenney" <paulmck@kernel.org>

The rcutorture_one_extend_check() function's last check assumes that
if cur_ops->readlock_nesting() returns greater than zero, either the
RCUTORTURE_RDR_RCU_1 or the RCUTORTURE_RDR_RCU_2 bit must be set, that
is, there must be at least one rcu_read_lock() in effect.

This works for preemptible RCU and for non-preemptible RCU running in
a non-preemptible kernel.  But it fails for non-preemptible RCU running
in a preemptible kernel because then RCU's cur_ops->readlock_nesting()
function, which is rcu_torture_readlock_nesting(), will return
the PREEMPT_MASK mask bits from preempt_count().  The result will
be greater than zero if preemption is disabled, including by the
RCUTORTURE_RDR_PREEMPT and RCUTORTURE_RDR_SCHED bits.

This commit therefore adjusts this check to take into account the case
fo non-preemptible RCU running in a preemptible kernel.

[boqun: Fix the if condition and add comment]

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202502171415.8ec87c87-lkp@intel.com
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Co-developed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcutorture.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d26fb1d33ed9..280bff706017 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1873,6 +1873,8 @@ static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp,
 #define ROEC_ARGS "%s %s: Current %#x  To add %#x  To remove %#x  preempt_count() %#x\n", __func__, s, curstate, new, old, preempt_count()
 static void rcutorture_one_extend_check(char *s, int curstate, int new, int old, bool insoftirq)
 {
+	int mask;
+
 	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST_CHK_RDR_STATE))
 		return;
 
@@ -1902,8 +1904,16 @@ static void rcutorture_one_extend_check(char *s, int curstate, int new, int old,
 	WARN_ONCE(cur_ops->extendables &&
 		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
 		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
-	WARN_ONCE(cur_ops->readlock_nesting &&
-		  !(curstate & (RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2)) &&
+
+	/*
+	 * non-preemptible RCU in a preemptible kernel uses "preempt_count() &
+	 * PREEMPT_MASK" as ->readlock_nesting().
+	 */
+	mask = RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
+	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
+		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
+
+	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
 		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
 }
 
-- 
2.39.5 (Apple Git-154)