[PATCH RFC tip/core/rcu] rcutorture: Limit reader duration if irq or bh disabled

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Hello, Thomas,

As discussed on IRC.  Thoughts?

							Thanx, Paul


commit 6ba3f37d31b614d7a41c3a1eb472dfc4e44944af
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date:   Fri Jul 20 12:04:12 2018 -0700

    rcutorture: Limit reader duration if irq or bh disabled
    
    There are debug checks in some environments that will complain if the
    duration of a bh-disabled region of code exceeds about 50 milliseconds.
    Because rcu_read_delay() can produce a 50-millisecond delay and because
    there could be up to eight reader segments with such delays, this commit
    limits the maximum delay to 10 milliseconds if either interrupts or
    softirqs are disabled.
    
    Reported-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 28af5db3e7d1..16735a3545d2 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -341,7 +341,7 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg * rtrsp)
 	unsigned long started;
 	unsigned long completed;
 	const unsigned long shortdelay_us = 200;
-	const unsigned long longdelay_ms = 300;
+	unsigned long longdelay_ms = 300;
 	unsigned long long ts;
 
 	/* We want a short delay sometimes to make a reader delay the grace
@@ -351,6 +351,8 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg * rtrsp)
 	if (!(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
 		started = cur_ops->get_gp_seq();
 		ts = rcu_trace_clock_local();
+		if (preempt_count() & (SOFTIRQ_MASK | HARDIRQ_MASK))
+			longdelay_ms = 5; /* Avoid triggering BH limits. */
 		mdelay(longdelay_ms);
 		rtrsp->rt_delay_ms = longdelay_ms;
 		completed = cur_ops->get_gp_seq();