Merge tag 'rcu.2023.08.21a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes, perhaps most notably simplifying
   SRCU_NOTIFIER_INIT() as suggested

 - RCU Tasks updates, most notably treating Tasks RCU callbacks as lazy
   while still treating synchronous grace periods as urgent. Also fixes
   one bug that restores the ability to apply debug-objects to RCU Tasks
   and another that fixes a race condition that could result in
   false-positive failures of the boot-time self-test code

 - RCU-scalability performance-test updates, most notably adding the
   ability to measure the RCU-Tasks's grace-period kthread's CPU
   consumption. This proved quite useful for the RCU Tasks work

 - Reference-acquisition/release performance-test updates, including a
   fix for an uninitialized wait_queue_head_t

 - Miscellaneous torture-test updates

 - Torture-test scripting updates, including removal of the
   non-longer-functional formal-verification scripts, test builds of
   individual RCU Tasks flavors, better diagnostics for loss of
   connectivity for distributed rcutorture tests, disabling of reboot
   loops in qemu/KVM-based rcutorture testing, and passing of init
   parameters to rcutorture's init program

* tag 'rcu.2023.08.21a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (64 commits)
  rcu: Use WRITE_ONCE() for assignments to ->next for rculist_nulls
  rcu: Make the rcu_nocb_poll boot parameter usable via boot config
  rcu: Mark __rcu_irq_enter_check_tick() ->rcu_urgent_qs load
  srcu,notifier: Remove #ifdefs in favor of SRCU Tiny srcu_usage
  rcutorture: Stop right-shifting torture_random() return values
  torture: Stop right-shifting torture_random() return values
  torture: Move stutter_wait() timeouts to hrtimers
  torture: Move torture_shuffle() timeouts to hrtimers
  torture: Move torture_onoff() timeouts to hrtimers
  torture: Make torture_hrtimeout_*() use TASK_IDLE
  torture: Add lock_torture writer_fifo module parameter
  torture: Add a kthread-creation callback to _torture_create_kthread()
  rcu-tasks: Fix boot-time RCU tasks debug-only deadlock
  rcu-tasks: Permit use of debug-objects with RCU Tasks flavors
  checkpatch: Complain about unexpected uses of RCU Tasks Trace
  torture: Cause mkinitrd.sh to indicate failure on compile errors
  torture: Make init program dump command-line arguments
  torture: Switch qemu from -nographic to -display none
  torture: Add init-program support for loongarch
  torture: Avoid torture-test reboot loops
  ...

1 files changed, 34 insertions, 3 deletions

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 1970ce5f22d4..91a0fd0d4d9a 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -528,6 +528,38 @@ static struct ref_scale_ops clock_ops = {
 	.name		= "clock"
 };
 
+static void ref_jiffies_section(const int nloops)
+{
+	u64 x = 0;
+	int i;
+
+	preempt_disable();
+	for (i = nloops; i >= 0; i--)
+		x += jiffies;
+	preempt_enable();
+	stopopts = x;
+}
+
+static void ref_jiffies_delay_section(const int nloops, const int udl, const int ndl)
+{
+	u64 x = 0;
+	int i;
+
+	preempt_disable();
+	for (i = nloops; i >= 0; i--) {
+		x += jiffies;
+		un_delay(udl, ndl);
+	}
+	preempt_enable();
+	stopopts = x;
+}
+
+static struct ref_scale_ops jiffies_ops = {
+	.readsection	= ref_jiffies_section,
+	.delaysection	= ref_jiffies_delay_section,
+	.name		= "jiffies"
+};
+
 ////////////////////////////////////////////////////////////////////////
 //
 // Methods leveraging SLAB_TYPESAFE_BY_RCU.
@@ -1047,7 +1079,7 @@ ref_scale_init(void)
 	int firsterr = 0;
 	static struct ref_scale_ops *scale_ops[] = {
 		&rcu_ops, &srcu_ops, RCU_TRACE_OPS RCU_TASKS_OPS &refcnt_ops, &rwlock_ops,
-		&rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops,
+		&rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops, &jiffies_ops,
 		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
 	};
 
@@ -1107,12 +1139,11 @@ ref_scale_init(void)
 	VERBOSE_SCALEOUT("Starting %d reader threads", nreaders);
 
 	for (i = 0; i < nreaders; i++) {
+		init_waitqueue_head(&reader_tasks[i].wq);
 		firsterr = torture_create_kthread(ref_scale_reader, (void *)i,
 						  reader_tasks[i].task);
 		if (torture_init_error(firsterr))
 			goto unwind;
-
-		init_waitqueue_head(&(reader_tasks[i].wq));
 	}
 
 	// Main Task