[PATCH 07/11] refscale: Ditch ref_scale_shutdown in favor of torture_shutdown_init()

[Paul E. McKenney]

The torture_shutdown_init() function spawns a shutdown kthread in
a manner very similar to that implemented by ref_scale_shutdown().
This commit therefore re-implements ref_scale_shutdown in terms of
torture_shutdown_init().

The initial draft of this patch was generated by version 2.1.16 of the
Claude AI/LLM, but trained and configured for use by my employer, and
prompted to refer to Linux-kernel source code.  This initial draft failed
to provide a forward reference to ref_scale_cleanup(), passed zero to
torture_shutdown_init() for an unwelcome insta-shutdown, and failed to
pass the kvm.sh --duration argument in as a refscale module parameter.
On the other hand, it did catch the need to NULL main_task on the
post-test self-shutdown code path, which I might well have forgotten
to do.

This version of the patch fixes those problems, and in fact very little
of the initial draft remains.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

[outline more of development process]

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/refscale.c                         | 51 +++++--------------
 .../configs/refscale/ver_functions.sh         |  2 +-
 2 files changed, 15 insertions(+), 38 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index c158b6a947cde..a2d9d75d88a10 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -92,15 +92,9 @@ torture_param(int, nreaders, -1, "Number of readers, -1 for 75% of CPUs.");
 torture_param(int, nruns, 30, "Number of experiments to run.");
 // Reader delay in nanoseconds, 0 for no delay.
 torture_param(int, readdelay, 0, "Read-side delay in nanoseconds.");
-
-#ifdef MODULE
-# define REFSCALE_SHUTDOWN 0
-#else
-# define REFSCALE_SHUTDOWN 1
-#endif
-
-torture_param(bool, shutdown, REFSCALE_SHUTDOWN,
-	      "Shutdown at end of scalability tests.");
+// Maximum shutdown delay in seconds, or zero for no shutdown.
+torture_param(int, shutdown_secs, !IS_MODULE(CONFIG_REPRO_TEST) * 300,
+	      "Shutdown at end of scalability tests or at specified timeout (s).");
 
 struct reader_task {
 	struct task_struct *task;
@@ -109,12 +103,8 @@ struct reader_task {
 	u64 last_duration_ns;
 };
 
-static struct task_struct *shutdown_task;
-static wait_queue_head_t shutdown_wq;
-
 static struct task_struct *main_task;
 static wait_queue_head_t main_wq;
-static int shutdown_start;
 
 static struct reader_task *reader_tasks;
 
@@ -1357,6 +1347,8 @@ static u64 process_durations(int n)
 	return sum;
 }
 
+static void ref_scale_cleanup(void);
+
 // The main_func is the main orchestrator, it performs a bunch of
 // experiments.  For every experiment, it orders all the readers
 // involved to start and waits for them to finish the experiment. It
@@ -1443,9 +1435,10 @@ static int main_func(void *arg)
 
 oom_exit:
 	// This will shutdown everything including us.
-	if (shutdown) {
-		shutdown_start = 1;
-		wake_up(&shutdown_wq);
+	if (shutdown_secs) {
+		main_task = NULL;  // Avoid self-kill deadlock.
+		ref_scale_cleanup();
+		kernel_power_off();
 	}
 
 	// Wait for torture to stop us
@@ -1463,8 +1456,8 @@ static void
 ref_scale_print_module_parms(const struct ref_scale_ops *cur_ops, const char *tag)
 {
 	pr_alert("%s" SCALE_FLAG
-		 "--- %s:  verbose=%d verbose_batched=%d shutdown=%d holdoff=%d lookup_instances=%ld loops=%d nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag,
-		 verbose, verbose_batched, shutdown, holdoff, lookup_instances, loops, nreaders, nruns, readdelay);
+		 "--- %s:  verbose=%d verbose_batched=%d shutdown_secs=%d holdoff=%d lookup_instances=%ld loops=%d nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag,
+		 verbose, verbose_batched, shutdown_secs, holdoff, lookup_instances, loops, nreaders, nruns, readdelay);
 }
 
 static void
@@ -1497,19 +1490,6 @@ ref_scale_cleanup(void)
 	torture_cleanup_end();
 }
 
-// Shutdown kthread.  Just waits to be awakened, then shuts down system.
-static int
-ref_scale_shutdown(void *arg)
-{
-	wait_event_idle(shutdown_wq, shutdown_start);
-
-	smp_mb(); // Wake before output.
-	ref_scale_cleanup();
-	kernel_power_off();
-
-	return -EINVAL;
-}
-
 static int __init
 ref_scale_init(void)
 {
@@ -1553,13 +1533,10 @@ ref_scale_init(void)
 	ref_scale_print_module_parms(cur_ops, "Start of test");
 
 	// Shutdown task
-	if (shutdown) {
-		init_waitqueue_head(&shutdown_wq);
-		firsterr = torture_create_kthread(ref_scale_shutdown, NULL,
-						  shutdown_task);
+	if (shutdown_secs) {
+		firsterr = torture_shutdown_init(shutdown_secs, ref_scale_cleanup);
 		if (torture_init_error(firsterr))
 			goto unwind;
-		schedule_timeout_uninterruptible(1);
 	}
 
 	// Reader tasks (default to ~75% of online CPUs).
@@ -1604,7 +1581,7 @@ ref_scale_init(void)
 unwind:
 	torture_init_end();
 	ref_scale_cleanup();
-	if (shutdown) {
+	if (shutdown_secs) {
 		WARN_ON(!IS_MODULE(CONFIG_RCU_REF_SCALE_TEST));
 		kernel_power_off();
 	}
diff --git a/tools/testing/selftests/rcutorture/configs/refscale/ver_functions.sh b/tools/testing/selftests/rcutorture/configs/refscale/ver_functions.sh
index 7484656276012..219fac070af28 100644
--- a/tools/testing/selftests/rcutorture/configs/refscale/ver_functions.sh
+++ b/tools/testing/selftests/rcutorture/configs/refscale/ver_functions.sh
@@ -11,7 +11,7 @@
 #
 # Adds per-version torture-module parameters to kernels supporting them.
 per_version_boot_params () {
-	echo	refscale.shutdown=1 \
+	echo	refscale.shutdown_secs=$3 \
 		refscale.verbose=0 \
 		$1
 }
-- 
2.40.1