Merge tag 'rcu.2022.05.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU update from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes

 - Callback-offloading updates, mainly simplifications

 - RCU-tasks updates, including some -rt fixups, handling of systems
   with sparse CPU numbering, and a fix for a boot-time race-condition
   failure

 - Put SRCU on a memory diet in order to reduce the size of the
   srcu_struct structure

 - Torture-test updates fixing some bugs in tests and closing some
   testing holes

 - Torture-test updates for the RCU tasks flavors, most notably ensuring
   that building rcutorture and friends does not change the
   RCU-tasks-related Kconfig options

 - Torture-test scripting updates

 - Expedited grace-period updates, most notably providing
   milliseconds-scale (not all that) soft real-time response from
   synchronize_rcu_expedited().

   This is also the first time in almost 30 years of RCU that someone
   other than me has pushed for a reduction in the RCU CPU stall-warning
   timeout, in this case by more than three orders of magnitude from 21
   seconds to 20 milliseconds. This tighter timeout applies only to
   expedited grace periods

* tag 'rcu.2022.05.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (80 commits)
  rcu: Move expedited grace period (GP) work to RT kthread_worker
  rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
  srcu: Drop needless initialization of sdp in srcu_gp_start()
  srcu: Prevent expedited GPs and blocking readers from consuming CPU
  srcu: Add contention check to call_srcu() srcu_data ->lock acquisition
  srcu: Automatically determine size-transition strategy at boot
  rcutorture: Make torture.sh allow for --kasan
  rcutorture: Make torture.sh refscale and rcuscale specify Tasks Trace RCU
  rcutorture: Make kvm.sh allow more memory for --kasan runs
  torture: Save "make allmodconfig" .config file
  scftorture: Remove extraneous "scf" from per_version_boot_params
  rcutorture: Adjust scenarios' Kconfig options for CONFIG_PREEMPT_DYNAMIC
  torture: Enable CSD-lock stall reports for scftorture
  torture: Skip vmlinux check for kvm-again.sh runs
  scftorture: Adjust for TASKS_RCU Kconfig option being selected
  rcuscale: Allow rcuscale without RCU Tasks Rude/Trace
  rcuscale: Allow rcuscale without RCU Tasks
  refscale: Allow refscale without RCU Tasks Rude/Trace
  refscale: Allow refscale without RCU Tasks
  rcutorture: Allow specifying per-scenario stat_interval
  ...

1 files changed, 10 insertions, 18 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 8360d86db1c0..c8ba0fe17267 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -486,6 +486,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 	t->rcu_read_unlock_special.s = 0;
 	if (special.b.need_qs) {
 		if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
+			rdp->cpu_no_qs.b.norm = false;
 			rcu_report_qs_rdp(rdp);
 			udelay(rcu_unlock_delay);
 		} else {
@@ -660,7 +661,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
 			    expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
 				// Get scheduler to re-evaluate and call hooks.
 				// If !IRQ_WORK, FQS scan will eventually IPI.
-				init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
+				if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
+				    IS_ENABLED(CONFIG_PREEMPT_RT))
+					rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
+								rcu_preempt_deferred_qs_handler);
+				else
+					init_irq_work(&rdp->defer_qs_iw,
+						      rcu_preempt_deferred_qs_handler);
 				rdp->defer_qs_iw_pending = true;
 				irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
 			}
@@ -1124,7 +1131,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 	__releases(rnp->lock)
 {
 	raw_lockdep_assert_held_rcu_node(rnp);
-	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+	if (!rnp->boost_kthread_task ||
+	    (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
@@ -1226,18 +1234,6 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 	free_cpumask_var(cm);
 }
 
-/*
- * Spawn boost kthreads -- called as soon as the scheduler is running.
- */
-static void __init rcu_spawn_boost_kthreads(void)
-{
-	struct rcu_node *rnp;
-
-	rcu_for_each_leaf_node(rnp)
-		if (rcu_rnp_online_cpus(rnp))
-			rcu_spawn_one_boost_kthread(rnp);
-}
-
 #else /* #ifdef CONFIG_RCU_BOOST */
 
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1263,10 +1259,6 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 {
 }
 
-static void __init rcu_spawn_boost_kthreads(void)
-{
-}
-
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*