[PATCH RFC tip/core/rcu 3/5] rcutorture: Ensure that normal GPs advance without expedited GPs

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

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Currently, rcutorture runs between 25% and 50% of grace periods as
expedited grace periods.  This means that on large configurations,
there are expected to be a number of expedited grace periods executing
concurrently with each normal grace period.  Now that normal grace periods
can be assisted by expedited grace periods, rcutorture would be unable to
detect a bug that prevented normal grace periods from completing if there
was no expedited grace period helping it.

This commit therefore alternates 30-second phases that run expedited
grace periods and 30-second phases that do not, so that this sort of
bug will provoke an RCU CPU stall warning.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/rcutorture.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 59aa76b4460e..c62c1c34d73c 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -54,6 +54,11 @@
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and Josh Triplett <josh@joshtriplett.org>");
 
+#ifdef CONFIG_RCU_CPU_STALL_TIMEOUT
+#define NOEXP_SECS_DEFAULT (CONFIG_RCU_CPU_STALL_TIMEOUT + 10)
+#else /* #ifdef CONFIG_RCU_CPU_STALL_TIMEOUT */
+#define NOEXP_SECS_DEFAULT 30
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_TIMEOUT */
 
 torture_param(int, cbflood_inter_holdoff, HZ,
 	      "Holdoff between floods (jiffies)");
@@ -75,6 +80,8 @@ torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers");
 torture_param(int, n_barrier_cbs, 0,
 	     "# of callbacks/kthreads for barrier testing");
 torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");
+torture_param(int, noexp_secs, NOEXP_SECS_DEFAULT,
+	      "Time to suppress/enable expedited GPs (s), 0 to disable");
 torture_param(int, nreaders, -1, "Number of RCU reader threads");
 torture_param(int, object_debug, 0,
 	     "Enable debug-object double call_rcu() testing");
@@ -192,6 +199,8 @@ static u64 notrace rcu_trace_clock_local(void)
 }
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
 
+static unsigned long rcutorture_noexp;
+
 static unsigned long boost_starttime;	/* jiffies of next boost test start. */
 static DEFINE_MUTEX(boost_mutex);	/* protect setting boost_starttime */
 					/*  and boost task create/destroy. */
@@ -894,6 +903,8 @@ rcu_torture_writer(void *arg)
 	bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal;
 	bool gp_sync1 = gp_sync;
 	int i;
+	int noexp_jiffies = noexp_secs * HZ;
+	unsigned long noexp_jiffies_next = jiffies - 1;
 	struct rcu_torture *rp;
 	struct rcu_torture *old_rp;
 	static DEFINE_TORTURE_RANDOM(rand);
@@ -942,6 +953,10 @@ rcu_torture_writer(void *arg)
 	do {
 		rcu_torture_writer_state = RTWS_FIXED_DELAY;
 		schedule_timeout_uninterruptible(1);
+		if (time_after(jiffies, noexp_jiffies_next)) {
+			rcutorture_noexp = jiffies + noexp_jiffies;
+			noexp_jiffies_next = rcutorture_noexp + noexp_jiffies;
+		}
 		rp = rcu_torture_alloc();
 		if (rp == NULL)
 			continue;
@@ -966,6 +981,9 @@ rcu_torture_writer(void *arg)
 				cur_ops->deferred_free(old_rp);
 				break;
 			case RTWS_EXP_SYNC:
+				if (time_before(jiffies, rcutorture_noexp) &&
+				    cur_ops->sync && gp_sync1)
+					goto noexp;
 				rcu_torture_writer_state = RTWS_EXP_SYNC;
 				cur_ops->exp_sync();
 				rcu_torture_pipe_update(old_rp);
@@ -982,6 +1000,7 @@ rcu_torture_writer(void *arg)
 				rcu_torture_pipe_update(old_rp);
 				break;
 			case RTWS_SYNC:
+noexp:
 				rcu_torture_writer_state = RTWS_SYNC;
 				cur_ops->sync();
 				rcu_torture_pipe_update(old_rp);
@@ -1036,7 +1055,8 @@ rcu_torture_fakewriter(void *arg)
 		    torture_random(&rand) % (nfakewriters * 8) == 0) {
 			cur_ops->cb_barrier();
 		} else if (gp_normal == gp_exp) {
-			if (torture_random(&rand) & 0x80)
+			if (time_before(jiffies, rcutorture_noexp) ||
+			    torture_random(&rand) & 0x80)
 				cur_ops->sync();
 			else
 				cur_ops->exp_sync();
-- 
1.8.1.5