[PATCH 09/11] rcutorture: Test RCU Tasks Trace GP implying RCU GP

["Paul E. McKenney" <paulmck@kernel.org>]

An RCU Tasks Trace grace period is supposed to imply an RCU grace period,
and this implication is relied on by BPF.  But this is not currently
tested.  This commit therefore makes tasks_tracing_torture_read_lock()
sometimes use rcu_read_lock() instead of rcu_read_lock_trace(), thus
testing the required implication.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/rcutorture.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index a0d27756141846..c8118c38812aee 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -766,11 +766,12 @@ srcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
 	const long uspertick = 1000000 / HZ;
 	const long longdelay = 10;
 
-	/* We want there to be long-running readers, but not all the time. */
+	// We want there to be long-running readers, but not all the time.
+	// The !rcu_preempt_depth() is for RCU Tasks Trace.
 
 	delay = torture_random(rrsp) %
 		(nrealreaders * 2 * longdelay * uspertick);
-	if (!delay && in_task() && !irqs_disabled()) {
+	if (!delay && !in_atomic() && !rcu_preempt_depth() && !irqs_disabled()) {
 		schedule_timeout_interruptible(longdelay);
 		rtrsp->rt_delay_jiffies = longdelay;
 	} else {
@@ -1219,15 +1220,24 @@ static struct rcu_torture_ops tasks_rude_ops = {
  * Definitions for tracing RCU-tasks torture testing.
  */
 
+// Note that an RCU Tasks Trace GP must imply an RCU GP.
 static int tasks_tracing_torture_read_lock(void)
 {
-	rcu_read_lock_trace();
-	return 0;
+	int use_rcu = !(jiffies & 0xff);
+
+	if (use_rcu)
+		rcu_read_lock();
+	else
+		rcu_read_lock_trace();
+	return use_rcu;
 }
 
-static void tasks_tracing_torture_read_unlock(int idx)
+static void tasks_tracing_torture_read_unlock(int use_rcu)
 {
-	rcu_read_unlock_trace();
+	if (use_rcu)
+		rcu_read_unlock();
+	else
+		rcu_read_unlock_trace();
 }
 
 static void rcu_tasks_tracing_torture_deferred_free(struct rcu_torture *p)
-- 
2.40.1