[PATCH] rcutorture: Create nocb tasks only for CONFIG_RCU_NOCB_CPU=y kernels

[Zqiang <qiang1.zhang@intel.com>]

When setting nocbs_nthreads to start rcutorture test with a non-zero value,
the nocb tasks will be created and invoke rcu_nocb_cpu_offload/deoffload()
to toggle CPU's callback-offload state, but for CONFIG_RCU_NOCB_CPU=n
kernel, the rcu_nocb_cpu_offload/deoffload() is a no-op and this is also
meaningless for torture_type is non-rcu.

This commit therefore add member can_nocbs_toggle to rcu_torture_ops
structure to avoid unnecessary nocb tasks creation.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
 kernel/rcu/rcutorture.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 297da28ce92d..27becacbe3b2 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -383,6 +383,7 @@ struct rcu_torture_ops {
 	long cbflood_max;
 	int irq_capable;
 	int can_boost;
+	int can_nocbs_toggle;
 	int extendables;
 	int slow_gps;
 	int no_pi_lock;
@@ -569,6 +570,7 @@ static struct rcu_torture_ops rcu_ops = {
 	.stall_dur		= rcu_jiffies_till_stall_check,
 	.irq_capable		= 1,
 	.can_boost		= IS_ENABLED(CONFIG_RCU_BOOST),
+	.can_nocbs_toggle	= IS_ENABLED(CONFIG_RCU_NOCB_CPU),
 	.extendables		= RCUTORTURE_MAX_EXTEND,
 	.name			= "rcu"
 };
@@ -2356,7 +2358,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
 		 "n_barrier_cbs=%d "
 		 "onoff_interval=%d onoff_holdoff=%d "
 		 "read_exit_delay=%d read_exit_burst=%d "
-		 "nocbs_nthreads=%d nocbs_toggle=%d "
+		 "nocbs_nthreads=%d/%d nocbs_toggle=%d "
 		 "test_nmis=%d\n",
 		 torture_type, tag, nrealreaders, nfakewriters,
 		 stat_interval, verbose, test_no_idle_hz, shuffle_interval,
@@ -2368,7 +2370,7 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
 		 n_barrier_cbs,
 		 onoff_interval, onoff_holdoff,
 		 read_exit_delay, read_exit_burst,
-		 nocbs_nthreads, nocbs_toggle,
+		 nocbs_nthreads, cur_ops->can_nocbs_toggle, nocbs_toggle,
 		 test_nmis);
 }
 
@@ -3708,6 +3710,10 @@ rcu_torture_init(void)
 		pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
 		fqs_duration = 0;
 	}
+	if (!cur_ops->can_nocbs_toggle && nocbs_nthreads > 0) {
+		pr_alert("rcu-torture: ->can_nocbs_toggle false and non-zero nocbs_nthreads, nocbs_toggle disabled.\n");
+		nocbs_nthreads = 0;
+	}
 	if (cur_ops->init)
 		cur_ops->init();
 
-- 
2.25.1