From 8002f93305f6af02d2bae5908520d4d92f82b6f9 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Fri, 24 Sep 2021 21:30:26 -0700
Subject: [PATCH] rcutorture: Suppress pi-lock-across read-unlock testing for
 Tiny SRCU

References: bnc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.17-rc0
Git-commit: 340170fef01b18631128006de03522b671e6e2b5

Because Tiny srcu_read_unlock() directly calls swake_up_one(), lockdep
complains when a pi lock is held across that srcu_read_unlock().
Although this is a lockdep false positive (there is no other CPU to
complete the deadlock cycle), lockdep is what it is at the moment.
This commit therefore prevents rcutorture from holding pi lock across
a Tiny srcu_read_unlock().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 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 d295da380fb4..503e14e62e8f 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -349,6 +349,7 @@ struct rcu_torture_ops {
 	int can_boost;
 	int extendables;
 	int slow_gps;
+	int no_pi_lock;
 	const char *name;
 };
 
@@ -670,6 +671,7 @@ static struct rcu_torture_ops srcu_ops = {
 	.cb_barrier	= srcu_torture_barrier,
 	.stats		= srcu_torture_stats,
 	.irq_capable	= 1,
+	.no_pi_lock	= IS_ENABLED(CONFIG_TINY_SRCU),
 	.name		= "srcu"
 };
 
@@ -703,6 +705,7 @@ static struct rcu_torture_ops srcud_ops = {
 	.cb_barrier	= srcu_torture_barrier,
 	.stats		= srcu_torture_stats,
 	.irq_capable	= 1,
+	.no_pi_lock	= IS_ENABLED(CONFIG_TINY_SRCU),
 	.name		= "srcud"
 };
 
@@ -723,6 +726,7 @@ static struct rcu_torture_ops busted_srcud_ops = {
 	.cb_barrier	= srcu_torture_barrier,
 	.stats		= srcu_torture_stats,
 	.irq_capable	= 1,
+	.no_pi_lock	= IS_ENABLED(CONFIG_TINY_SRCU),
 	.extendables	= RCUTORTURE_MAX_EXTEND,
 	.name		= "busted_srcud"
 };
@@ -1473,8 +1477,9 @@ static void rcutorture_one_extend(int *readstate, int newstate,
 		idxold2 = 0;
 	}
 	if (statesold & RCUTORTURE_RDR_RCU_1) {
-		bool lockit = !statesnew && !(torture_random(trsp) & 0xffff);
+		bool lockit;
 
+		lockit = !cur_ops->no_pi_lock && !statesnew && !(torture_random(trsp) & 0xffff);
 		if (lockit)
 			raw_spin_lock_irqsave(&current->pi_lock, flags);
 		cur_ops->readunlock((idxold1 >> RCUTORTURE_RDR_SHIFT_1) & 0x1);