From 8bde20066317529b2c26771c7595612a4b4d726b Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Sun, 16 May 2021 21:17:27 -0700
Subject: [PATCH] rcutorture: Preempt rather than block when testing task
 stalls

References: bnc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.15-rc1
Git-commit: 59e836662860a28880d45b35e1fbc5afca4847ce

Currently, rcu_torture_stall() does a one-jiffy timed wait when
stall_cpu_block is set.  This works, but emits a pointless splat in
CONFIG_PREEMPT=y kernels.  This commit avoids this splat by instead
invoking preempt_schedule() in CONFIG_PREEMPT=y kernels.

This uses an admittedly ugly #ifdef, but abstracted approaches just
looked worse.  A prettier approach would provide a preempt_schedule()
definition with a WARN_ON() for CONFIG_PREEMPT=n kernels, but this seems
quite silly.

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 d2ef535530b1..968696ace8f3 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2046,8 +2046,13 @@ static int rcu_torture_stall(void *args)
 			  __func__, raw_smp_processor_id());
 		while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(),
 				    stop_at))
-			if (stall_cpu_block)
+			if (stall_cpu_block) {
+#ifdef CONFIG_PREEMPTION
+				preempt_schedule();
+#else
 				schedule_timeout_uninterruptible(HZ);
+#endif
+			}
 		if (stall_cpu_irqsoff)
 			local_irq_enable();
 		else if (!stall_cpu_block)