[PATCH RFC v2 15/24] hazptrtorture: Add the ability to disable the writer kthread

This commit adds a hazptrtorture.nwriters module parameter that, when set
to zero, disables hazard-pointer update-side activity.

Signed-off-by: Paul E. McKenney <[email protected]>
---
 kernel/rcu/hazptrtorture.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/hazptrtorture.c b/kernel/rcu/hazptrtorture.c
index 625ed90912a2c6..0752cedb2f5570 100644
--- a/kernel/rcu/hazptrtorture.c
+++ b/kernel/rcu/hazptrtorture.c
@@ -36,6 +36,7 @@ torture_param(int, irq_acquire, -1,
 torture_param(int, kthread_do_pending_ms, -1,
 	      "Delay between cleanups for deferred hazard pointers (ms), zero to disable");
 torture_param(int, nreaders, -1, "Number of hazard-pointer reader threads");
+torture_param(int, nwriters, 1, "Number of hazard-pointer writer threads, 0 or 1");
 torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
 torture_param(int, onoff_interval, 0, "Time between CPU hotplugs (jiffies), 0=disable");
 torture_param(int, preempt_duration, 0, "Preemption duration (ms), zero to disable");
@@ -658,14 +659,14 @@ static void
 hazptr_torture_print_module_parms(struct hazptr_torture_ops *cur_ops, const char *tag)
 {
 	pr_alert("%s" TORTURE_FLAG
-		 "--- %s: nreaders=%d "
+		 "--- %s: nreaders=%d nwriters=%d "
 		 "defer_modulus=%d irq_acquire=%d kthread_do_pending_ms=%d "
 		 "onoff_interval=%d onoff_holdoff=%d "
 		 "preempt_duration=%d preempt_interval=%d "
 		 "reader_sleep_us=%d "
 		 "shuffle_interval=%d shutdown_secs=%d stat_interval=%d stutter=%d "
 		 "verbose=%d\n",
-		 torture_type, tag, nrealreaders,
+		 torture_type, tag, nrealreaders, nwriters,
 		 defer_modulus, irq_acquire, kthread_do_pending_ms,
 		 onoff_interval, onoff_holdoff,
 		 preempt_duration, preempt_interval,
@@ -825,9 +826,12 @@ static int __init hazptr_torture_init(void)
 			goto unwind;
 	}
 
-	firsterr = torture_create_kthread(hazptr_torture_writer, NULL, writer_task);
-	if (torture_init_error(firsterr))
-		goto unwind;
+	if (nwriters) {
+		WARN_ON(IS_BUILTIN(CONFIG_HAZPTR_TORTURE_TEST) && nwriters != 1);
+		firsterr = torture_create_kthread(hazptr_torture_writer, NULL, writer_task);
+		if (torture_init_error(firsterr))
+			goto unwind;
+	}
 
 	firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval, NULL);
 	if (torture_init_error(firsterr))
-- 
2.40.1