Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The main RCU related changes in this cycle were:

   - Additional cleanups after RCU flavor consolidation

   - Grace-period forward-progress cleanups and improvements

   - Documentation updates

   - Miscellaneous fixes

   - spin_is_locked() conversions to lockdep

   - SPDX changes to RCU source and header files

   - SRCU updates

   - Torture-test updates, including nolibc updates and moving nolibc to
     tools/include"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (71 commits)
  locking/locktorture: Convert to SPDX license identifier
  linux/torture: Convert to SPDX license identifier
  torture: Convert to SPDX license identifier
  linux/srcu: Convert to SPDX license identifier
  linux/rcutree: Convert to SPDX license identifier
  linux/rcutiny: Convert to SPDX license identifier
  linux/rcu_sync: Convert to SPDX license identifier
  linux/rcu_segcblist: Convert to SPDX license identifier
  linux/rcupdate: Convert to SPDX license identifier
  linux/rcu_node_tree: Convert to SPDX license identifier
  rcu/update: Convert to SPDX license identifier
  rcu/tree: Convert to SPDX license identifier
  rcu/tiny: Convert to SPDX license identifier
  rcu/sync: Convert to SPDX license identifier
  rcu/srcu: Convert to SPDX license identifier
  rcu/rcutorture: Convert to SPDX license identifier
  rcu/rcu_segcblist: Convert to SPDX license identifier
  rcu/rcuperf: Convert to SPDX license identifier
  rcu/rcu.h: Convert to SPDX license identifier
  RCU/torture.txt: Remove section MODULE PARAMETERS
  ...

14 files changed, 390 insertions, 650 deletions

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index a393e24a9195..acee72c0b24b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -1,23 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Read-Copy Update definitions shared among RCU implementations.
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2011
  *
- * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ * Author: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #ifndef __LINUX_RCU_H
@@ -30,7 +17,7 @@
 #define RCU_TRACE(stmt)
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
 
-/* Offset to allow for unmatched rcu_irq_{enter,exit}(). */
+/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
 #define DYNTICK_IRQ_NONIDLE	((LONG_MAX / 2) + 1)
 
 
@@ -462,8 +449,6 @@ void rcu_request_urgent_qs_task(struct task_struct *t);
 
 enum rcutorture_type {
 	RCU_FLAVOR,
-	RCU_BH_FLAVOR,
-	RCU_SCHED_FLAVOR,
 	RCU_TASKS_FLAVOR,
 	SRCU_FLAVOR,
 	INVALID_RCU_FLAVOR
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 5aff271adf1e..9bd5f6023c21 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -1,23 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * RCU segmented callback lists, function definitions
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2017
  *
- * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #include <linux/types.h>
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 948470cef385..71b64648464e 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -1,23 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * RCU segmented callback lists, internal-to-rcu header file
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2017
  *
- * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #include <linux/rcu_segcblist.h>
diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
index b459da70b4fc..c29761152874 100644
--- a/kernel/rcu/rcuperf.c
+++ b/kernel/rcu/rcuperf.c
@@ -1,23 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Read-Copy Update module-based performance-test facility
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright (C) IBM Corporation, 2015
  *
- * Authors: Paul E. McKenney <paulmck@us.ibm.com>
+ * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #define pr_fmt(fmt) fmt
@@ -54,7 +41,7 @@
 #include "rcu.h"
 
 MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.vnet.ibm.com>");
+MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com>");
 
 #define PERF_FLAG "-perf:"
 #define PERFOUT_STRING(s) \
@@ -83,13 +70,19 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.vnet.ibm.com>");
  * Various other use cases may of course be specified.
  */
 
+#ifdef MODULE
+# define RCUPERF_SHUTDOWN 0
+#else
+# define RCUPERF_SHUTDOWN 1
+#endif
+
 torture_param(bool, gp_async, false, "Use asynchronous GP wait primitives");
 torture_param(int, gp_async_max, 1000, "Max # outstanding waits per reader");
 torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
 torture_param(int, holdoff, 10, "Holdoff time before test start (s)");
 torture_param(int, nreaders, -1, "Number of RCU reader threads");
 torture_param(int, nwriters, -1, "Number of RCU updater threads");
-torture_param(bool, shutdown, !IS_ENABLED(MODULE),
+torture_param(bool, shutdown, RCUPERF_SHUTDOWN,
 	      "Shutdown at end of performance tests.");
 torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
 torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f6e85faa4ff4..f14d1b18a74f 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1,23 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Read-Copy Update module-based torture test facility
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright (C) IBM Corporation, 2005, 2006
  *
- * Authors: Paul E. McKenney <paulmck@us.ibm.com>
+ * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
  *	  Josh Triplett <josh@joshtriplett.org>
  *
  * See also:  Documentation/RCU/torture.txt
@@ -61,7 +48,7 @@
 #include "rcu.h"
 
 MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and Josh Triplett <josh@joshtriplett.org>");
+MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com> and Josh Triplett <josh@joshtriplett.org>");
 
 
 /* Bits for ->extendables field, extendables param, and related definitions. */
@@ -1630,21 +1617,34 @@ static bool rcu_fwd_emergency_stop;
 #define MIN_FWD_CB_LAUNDERS	3	/* This many CB invocations to count. */
 #define MIN_FWD_CBS_LAUNDERED	100	/* Number of counted CBs. */
 #define FWD_CBS_HIST_DIV	10	/* Histogram buckets/second. */
-static long n_launders_hist[2 * MAX_FWD_CB_JIFFIES / (HZ / FWD_CBS_HIST_DIV)];
+struct rcu_launder_hist {
+	long n_launders;
+	unsigned long launder_gp_seq;
+};
+#define N_LAUNDERS_HIST (2 * MAX_FWD_CB_JIFFIES / (HZ / FWD_CBS_HIST_DIV))
+static struct rcu_launder_hist n_launders_hist[N_LAUNDERS_HIST];
+static unsigned long rcu_launder_gp_seq_start;
 
 static void rcu_torture_fwd_cb_hist(void)
 {
+	unsigned long gps;
+	unsigned long gps_old;
 	int i;
 	int j;
 
 	for (i = ARRAY_SIZE(n_launders_hist) - 1; i > 0; i--)
-		if (n_launders_hist[i] > 0)
+		if (n_launders_hist[i].n_launders > 0)
 			break;
 	pr_alert("%s: Callback-invocation histogram (duration %lu jiffies):",
 		 __func__, jiffies - rcu_fwd_startat);
-	for (j = 0; j <= i; j++)
-		pr_cont(" %ds/%d: %ld",
-			j + 1, FWD_CBS_HIST_DIV, n_launders_hist[j]);
+	gps_old = rcu_launder_gp_seq_start;
+	for (j = 0; j <= i; j++) {
+		gps = n_launders_hist[j].launder_gp_seq;
+		pr_cont(" %ds/%d: %ld:%ld",
+			j + 1, FWD_CBS_HIST_DIV, n_launders_hist[j].n_launders,
+			rcutorture_seq_diff(gps, gps_old));
+		gps_old = gps;
+	}
 	pr_cont("\n");
 }
 
@@ -1666,7 +1666,8 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
 	i = ((jiffies - rcu_fwd_startat) / (HZ / FWD_CBS_HIST_DIV));
 	if (i >= ARRAY_SIZE(n_launders_hist))
 		i = ARRAY_SIZE(n_launders_hist) - 1;
-	n_launders_hist[i]++;
+	n_launders_hist[i].n_launders++;
+	n_launders_hist[i].launder_gp_seq = cur_ops->get_gp_seq();
 	spin_unlock_irqrestore(&rcu_fwd_lock, flags);
 }
 
@@ -1786,9 +1787,10 @@ static void rcu_torture_fwd_prog_cr(void)
 	n_max_cbs = 0;
 	n_max_gps = 0;
 	for (i = 0; i < ARRAY_SIZE(n_launders_hist); i++)
-		n_launders_hist[i] = 0;
+		n_launders_hist[i].n_launders = 0;
 	cver = READ_ONCE(rcu_torture_current_version);
 	gps = cur_ops->get_gp_seq();
+	rcu_launder_gp_seq_start = gps;
 	while (time_before(jiffies, stopat) &&
 	       !READ_ONCE(rcu_fwd_emergency_stop) && !torture_must_stop()) {
 		rfcp = READ_ONCE(rcu_fwd_cb_head);
@@ -2228,6 +2230,14 @@ static void rcu_test_debug_objects(void)
 #endif /* #else #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 }
 
+static void rcutorture_sync(void)
+{
+	static unsigned long n;
+
+	if (cur_ops->sync && !(++n & 0xfff))
+		cur_ops->sync();
+}
+
 static int __init
 rcu_torture_init(void)
 {
@@ -2389,7 +2399,8 @@ rcu_torture_init(void)
 	firsterr = torture_shutdown_init(shutdown_secs, rcu_torture_cleanup);
 	if (firsterr)
 		goto unwind;
-	firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval);
+	firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval,
+				      rcutorture_sync);
 	if (firsterr)
 		goto unwind;
 	firsterr = rcu_torture_stall_init();
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 32dfd6522548..5d4a39a6505a 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -1,24 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Sleepable Read-Copy Update mechanism for mutual exclusion,
  *	tiny version for non-preemptible single-CPU use.
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright (C) IBM Corporation, 2017
  *
- * Author: Paul McKenney <paulmck@us.ibm.com>
+ * Author: Paul McKenney <paulmck@linux.ibm.com>
  */
 
 #include <linux/export.h>
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 3600d88d8956..a60b8ba9e1ac 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1,24 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Sleepable Read-Copy Update mechanism for mutual exclusion.
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright (C) IBM Corporation, 2006
  * Copyright (C) Fujitsu, 2012
  *
- * Author: Paul McKenney <paulmck@us.ibm.com>
+ * Author: Paul McKenney <paulmck@linux.ibm.com>
  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
@@ -58,6 +45,7 @@ static bool __read_mostly srcu_init_done;
 static void srcu_invoke_callbacks(struct work_struct *work);
 static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay);
 static void process_srcu(struct work_struct *work);
+static void srcu_delay_timer(struct timer_list *t);
 
 /* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
 #define spin_lock_rcu_node(p)					\
@@ -156,7 +144,8 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
 			snp->grphi = cpu;
 		}
 		sdp->cpu = cpu;
-		INIT_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks);
+		INIT_WORK(&sdp->work, srcu_invoke_callbacks);
+		timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
 		sdp->ssp = ssp;
 		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
 		if (is_static)
@@ -386,13 +375,19 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
 	} else {
 		flush_delayed_work(&ssp->work);
 	}
-	for_each_possible_cpu(cpu)
+	for_each_possible_cpu(cpu) {
+		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
+
 		if (quiesced) {
-			if (WARN_ON(delayed_work_pending(&per_cpu_ptr(ssp->sda, cpu)->work)))
+			if (WARN_ON(timer_pending(&sdp->delay_work)))
+				return; /* Just leak it! */
+			if (WARN_ON(work_pending(&sdp->work)))
 				return; /* Just leak it! */
 		} else {
-			flush_delayed_work(&per_cpu_ptr(ssp->sda, cpu)->work);
+			del_timer_sync(&sdp->delay_work);
+			flush_work(&sdp->work);
 		}
+	}
 	if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
 	    WARN_ON(srcu_readers_active(ssp))) {
 		pr_info("%s: Active srcu_struct %p state: %d\n",
@@ -463,39 +458,23 @@ static void srcu_gp_start(struct srcu_struct *ssp)
 	WARN_ON_ONCE(state != SRCU_STATE_SCAN1);
 }
 
-/*
- * Track online CPUs to guide callback workqueue placement.
- */
-DEFINE_PER_CPU(bool, srcu_online);
 
-void srcu_online_cpu(unsigned int cpu)
+static void srcu_delay_timer(struct timer_list *t)
 {
-	WRITE_ONCE(per_cpu(srcu_online, cpu), true);
-}
+	struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work);
 
-void srcu_offline_cpu(unsigned int cpu)
-{
-	WRITE_ONCE(per_cpu(srcu_online, cpu), false);
+	queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
 }
 
-/*
- * Place the workqueue handler on the specified CPU if online, otherwise
- * just run it whereever.  This is useful for placing workqueue handlers
- * that are to invoke the specified CPU's callbacks.
- */
-static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
-				       struct delayed_work *dwork,
+static void srcu_queue_delayed_work_on(struct srcu_data *sdp,
 				       unsigned long delay)
 {
-	bool ret;
+	if (!delay) {
+		queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
+		return;
+	}
 
-	preempt_disable();
-	if (READ_ONCE(per_cpu(srcu_online, cpu)))
-		ret = queue_delayed_work_on(cpu, wq, dwork, delay);
-	else
-		ret = queue_delayed_work(wq, dwork, delay);
-	preempt_enable();
-	return ret;
+	timer_reduce(&sdp->delay_work, jiffies + delay);
 }
 
 /*
@@ -504,7 +483,7 @@ static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
  */
 static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
 {
-	srcu_queue_delayed_work_on(sdp->cpu, rcu_gp_wq, &sdp->work, delay);
+	srcu_queue_delayed_work_on(sdp, delay);
 }
 
 /*
@@ -1186,7 +1165,8 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 	struct srcu_data *sdp;
 	struct srcu_struct *ssp;
 
-	sdp = container_of(work, struct srcu_data, work.work);
+	sdp = container_of(work, struct srcu_data, work);
+
 	ssp = sdp->ssp;
 	rcu_cblist_init(&ready_cbs);
 	spin_lock_irq_rcu_node(sdp);
diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index be10036fa621..a8304d90573f 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -1,20 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * RCU-based infrastructure for lightweight reader-writer locking
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright (c) 2015, Red Hat, Inc.
  *
  * Author: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 5f5963ba313e..911bd9076d43 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -1,23 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2008
  *
- * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ * Author: Paul E. McKenney <paulmck@linux.ibm.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
  *		Documentation/RCU
@@ -76,7 +63,7 @@ void rcu_qs(void)
  * be called from hardirq context.  It is normally called from the
  * scheduling-clock interrupt.
  */
-void rcu_check_callbacks(int user)
+void rcu_sched_clock_irq(int user)
 {
 	if (user) {
 		rcu_qs();
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9180158756d2..3b084dbfb4bc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1,27 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Read-Copy Update mechanism for mutual exclusion
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2008
  *
  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  *	    Manfred Spraul <manfred@colorfullife.com>
- *	    Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
+ *	    Paul E. McKenney <paulmck@linux.ibm.com> Hierarchical version
  *
- * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
+ * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  *
  * For detailed explanation of Read-Copy Update mechanism see -
@@ -62,6 +49,7 @@
 #include <linux/suspend.h>
 #include <linux/ftrace.h>
 #include <linux/tick.h>
+#include <linux/sysrq.h>
 
 #include "tree.h"
 #include "rcu.h"
@@ -115,6 +103,9 @@ int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
 /* panic() on RCU Stall sysctl. */
 int sysctl_panic_on_rcu_stall __read_mostly;
+/* Commandeer a sysrq key to dump RCU's tree. */
+static bool sysrq_rcu;
+module_param(sysrq_rcu, bool, 0444);
 
 /*
  * The rcu_scheduler_active variable is initialized to the value
@@ -479,7 +470,6 @@ module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next
 module_param(rcu_kick_kthreads, bool, 0644);
 
 static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
-static void force_quiescent_state(void);
 static int rcu_pending(void);
 
 /*
@@ -504,13 +494,12 @@ unsigned long rcu_exp_batches_completed(void)
 EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
 
 /*
- * Force a quiescent state.
+ * Return the root node of the rcu_state structure.
  */
-void rcu_force_quiescent_state(void)
+static struct rcu_node *rcu_get_root(void)
 {
-	force_quiescent_state();
+	return &rcu_state.node[0];
 }
-EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 
 /*
  * Convert a ->gp_state value to a character string.
@@ -529,19 +518,30 @@ void show_rcu_gp_kthreads(void)
 {
 	int cpu;
 	unsigned long j;
+	unsigned long ja;
+	unsigned long jr;
+	unsigned long jw;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
 
-	j = jiffies - READ_ONCE(rcu_state.gp_activity);
-	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %ld\n",
+	j = jiffies;
+	ja = j - READ_ONCE(rcu_state.gp_activity);
+	jr = j - READ_ONCE(rcu_state.gp_req_activity);
+	jw = j - READ_ONCE(rcu_state.gp_wake_time);
+	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
-		rcu_state.gp_state, rcu_state.gp_kthread->state, j);
+		rcu_state.gp_state,
+		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
+		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
+		(long)READ_ONCE(rcu_state.gp_seq),
+		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
+		READ_ONCE(rcu_state.gp_flags));
 	rcu_for_each_node_breadth_first(rnp) {
 		if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
 			continue;
-		pr_info("\trcu_node %d:%d ->gp_seq %lu ->gp_seq_needed %lu\n",
-			rnp->grplo, rnp->grphi, rnp->gp_seq,
-			rnp->gp_seq_needed);
+		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
+			rnp->grplo, rnp->grphi, (long)rnp->gp_seq,
+			(long)rnp->gp_seq_needed);
 		if (!rcu_is_leaf_node(rnp))
 			continue;
 		for_each_leaf_node_possible_cpu(rnp, cpu) {
@@ -550,14 +550,35 @@ void show_rcu_gp_kthreads(void)
 			    ULONG_CMP_GE(rcu_state.gp_seq,
 					 rdp->gp_seq_needed))
 				continue;
-			pr_info("\tcpu %d ->gp_seq_needed %lu\n",
-				cpu, rdp->gp_seq_needed);
+			pr_info("\tcpu %d ->gp_seq_needed %ld\n",
+				cpu, (long)rdp->gp_seq_needed);
 		}
 	}
 	/* sched_show_task(rcu_state.gp_kthread); */
 }
 EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
 
+/* Dump grace-period-request information due to commandeered sysrq. */
+static void sysrq_show_rcu(int key)
+{
+	show_rcu_gp_kthreads();
+}
+
+static struct sysrq_key_op sysrq_rcudump_op = {
+	.handler = sysrq_show_rcu,
+	.help_msg = "show-rcu(y)",
+	.action_msg = "Show RCU tree",
+	.enable_mask = SYSRQ_ENABLE_DUMP,
+};
+
+static int __init rcu_sysrq_init(void)
+{
+	if (sysrq_rcu)
+		return register_sysrq_key('y', &sysrq_rcudump_op);
+	return 0;
+}
+early_initcall(rcu_sysrq_init);
+
 /*
  * Send along grace-period-related data for rcutorture diagnostics.
  */
@@ -566,8 +587,6 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 {
 	switch (test_type) {
 	case RCU_FLAVOR:
-	case RCU_BH_FLAVOR:
-	case RCU_SCHED_FLAVOR:
 		*flags = READ_ONCE(rcu_state.gp_flags);
 		*gp_seq = rcu_seq_current(&rcu_state.gp_seq);
 		break;
@@ -578,14 +597,6 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
 
 /*
- * Return the root node of the rcu_state structure.
- */
-static struct rcu_node *rcu_get_root(void)
-{
-	return &rcu_state.node[0];
-}
-
-/*
  * Enter an RCU extended quiescent state, which can be either the
  * idle loop or adaptive-tickless usermode execution.
  *
@@ -701,7 +712,6 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
 
 /**
  * rcu_nmi_exit - inform RCU of exit from NMI context
- * @irq: Is this call from rcu_irq_exit?
  *
  * If you add or remove a call to rcu_nmi_exit(), be sure to test
  * with CONFIG_RCU_EQS_DEBUG=y.
@@ -1115,7 +1125,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	}
 
 	/*
-	 * NO_HZ_FULL CPUs can run in-kernel without rcu_check_callbacks!
+	 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
 	 * The above code handles this, but only for straight cond_resched().
 	 * And some in-kernel loops check need_resched() before calling
 	 * cond_resched(), which defeats the above code for CPUs that are
@@ -1181,7 +1191,7 @@ static void rcu_check_gp_kthread_starvation(void)
 		pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
 		       rcu_state.name, j,
 		       (long)rcu_seq_current(&rcu_state.gp_seq),
-		       rcu_state.gp_flags,
+		       READ_ONCE(rcu_state.gp_flags),
 		       gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
 		       gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
 		if (gpk) {
@@ -1310,7 +1320,7 @@ static void print_other_cpu_stall(unsigned long gp_seq)
 
 	panic_on_rcu_stall();
 
-	force_quiescent_state();  /* Kick them all. */
+	rcu_force_quiescent_state();  /* Kick them all. */
 }
 
 static void print_cpu_stall(void)
@@ -1557,17 +1567,28 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
 }
 
 /*
- * Awaken the grace-period kthread.  Don't do a self-awaken, and don't
- * bother awakening when there is nothing for the grace-period kthread
- * to do (as in several CPUs raced to awaken, and we lost), and finally
- * don't try to awaken a kthread that has not yet been created.
+ * Awaken the grace-period kthread.  Don't do a self-awaken (unless in
+ * an interrupt or softirq handler), and don't bother awakening when there
+ * is nothing for the grace-period kthread to do (as in several CPUs raced
+ * to awaken, and we lost), and finally don't try to awaken a kthread that
+ * has not yet been created.  If all those checks are passed, track some
+ * debug information and awaken.
+ *
+ * So why do the self-wakeup when in an interrupt or softirq handler
+ * in the grace-period kthread's context?  Because the kthread might have
+ * been interrupted just as it was going to sleep, and just after the final
+ * pre-sleep check of the awaken condition.  In this case, a wakeup really
+ * is required, and is therefore supplied.
  */
 static void rcu_gp_kthread_wake(void)
 {
-	if (current == rcu_state.gp_kthread ||
+	if ((current == rcu_state.gp_kthread &&
+	     !in_interrupt() && !in_serving_softirq()) ||
 	    !READ_ONCE(rcu_state.gp_flags) ||
 	    !rcu_state.gp_kthread)
 		return;
+	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
+	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
 	swake_up_one(&rcu_state.gp_wq);
 }
 
@@ -1711,7 +1732,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
 		zero_cpu_stall_ticks(rdp);
 	}
 	rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */
-	if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap)
+	if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
 		rdp->gp_seq_needed = rnp->gp_seq_needed;
 	WRITE_ONCE(rdp->gpwrap, false);
 	rcu_gpnum_ovf(rnp, rdp);
@@ -1939,7 +1960,7 @@ static void rcu_gp_fqs_loop(void)
 		if (!ret) {
 			rcu_state.jiffies_force_qs = jiffies + j;
 			WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
-				   jiffies + 3 * j);
+				   jiffies + (j ? 3 * j : 2));
 		}
 		trace_rcu_grace_period(rcu_state.name,
 				       READ_ONCE(rcu_state.gp_seq),
@@ -2497,14 +2518,14 @@ static void rcu_do_batch(struct rcu_data *rdp)
 }
 
 /*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context.  It is normally
- * invoked from the scheduling-clock interrupt.
+ * This function is invoked from each scheduling-clock interrupt,
+ * and checks to see if this CPU is in a non-context-switch quiescent
+ * state, for example, user mode or idle loop.  It also schedules RCU
+ * core processing.  If the current grace period has gone on too long,
+ * it will ask the scheduler to manufacture a context switch for the sole
+ * purpose of providing a providing the needed quiescent state.
  */
-void rcu_check_callbacks(int user)
+void rcu_sched_clock_irq(int user)
 {
 	trace_rcu_utilization(TPS("Start scheduler-tick"));
 	raw_cpu_inc(rcu_data.ticks_this_gp);
@@ -2517,7 +2538,7 @@ void rcu_check_callbacks(int user)
 		}
 		__this_cpu_write(rcu_data.rcu_urgent_qs, false);
 	}
-	rcu_flavor_check_callbacks(user);
+	rcu_flavor_sched_clock_irq(user);
 	if (rcu_pending())
 		invoke_rcu_core();
 
@@ -2578,7 +2599,7 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
  * Force quiescent states on reluctant CPUs, and also detect which
  * CPUs are in dyntick-idle mode.
  */
-static void force_quiescent_state(void)
+void rcu_force_quiescent_state(void)
 {
 	unsigned long flags;
 	bool ret;
@@ -2610,6 +2631,7 @@ static void force_quiescent_state(void)
 	raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
 	rcu_gp_kthread_wake();
 }
+EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 
 /*
  * This function checks for grace-period requests that fail to motivate
@@ -2657,16 +2679,11 @@ rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
-	pr_alert("%s: g%ld->%ld gar:%lu ga:%lu f%#x gs:%d %s->state:%#lx\n",
-		 __func__, (long)READ_ONCE(rcu_state.gp_seq),
-		 (long)READ_ONCE(rnp_root->gp_seq_needed),
-		 j - rcu_state.gp_req_activity, j - rcu_state.gp_activity,
-		 rcu_state.gp_flags, rcu_state.gp_state, rcu_state.name,
-		 rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL);
 	WARN_ON(1);
 	if (rnp_root != rnp)
 		raw_spin_unlock_rcu_node(rnp_root);
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	show_rcu_gp_kthreads();
 }
 
 /*
@@ -2711,12 +2728,8 @@ void rcu_fwd_progress_check(unsigned long j)
 }
 EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
 
-/*
- * This does the RCU core processing work for the specified rcu_data
- * structures.  This may be called only from the CPU to whom the rdp
- * belongs.
- */
-static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
+/* Perform RCU core processing work for the current CPU.  */
+static __latent_entropy void rcu_core(struct softirq_action *unused)
 {
 	unsigned long flags;
 	struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
@@ -2801,9 +2814,9 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
 
 	/*
 	 * Force the grace period if too many callbacks or too long waiting.
-	 * Enforce hysteresis, and don't invoke force_quiescent_state()
+	 * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
 	 * if some other CPU has recently done so.  Also, don't bother
-	 * invoking force_quiescent_state() if the newly enqueued callback
+	 * invoking rcu_force_quiescent_state() if the newly enqueued callback
 	 * is the only one waiting for a grace period to complete.
 	 */
 	if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
@@ -2820,7 +2833,7 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
 			rdp->blimit = LONG_MAX;
 			if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&
 			    rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
-				force_quiescent_state();
+				rcu_force_quiescent_state();
 			rdp->n_force_qs_snap = rcu_state.n_force_qs;
 			rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
 		}
@@ -2889,9 +2902,6 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func, int cpu, bool lazy)
 			rcu_segcblist_init(&rdp->cblist);
 	}
 	rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
-	if (!lazy)
-		rcu_idle_count_callbacks_posted();
-
 	if (__is_kfree_rcu_offset((unsigned long)func))
 		trace_rcu_kfree_callback(rcu_state.name, head,
 					 (unsigned long)func,
@@ -2961,6 +2971,79 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 }
 EXPORT_SYMBOL_GPL(kfree_call_rcu);
 
+/*
+ * During early boot, any blocking grace-period wait automatically
+ * implies a grace period.  Later on, this is never the case for PREEMPT.
+ *
+ * Howevr, because a context switch is a grace period for !PREEMPT, any
+ * blocking grace-period wait automatically implies a grace period if
+ * there is only one CPU online at any point time during execution of
+ * either synchronize_rcu() or synchronize_rcu_expedited().  It is OK to
+ * occasionally incorrectly indicate that there are multiple CPUs online
+ * when there was in fact only one the whole time, as this just adds some
+ * overhead: RCU still operates correctly.
+ */
+static int rcu_blocking_is_gp(void)
+{
+	int ret;
+
+	if (IS_ENABLED(CONFIG_PREEMPT))
+		return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
+	might_sleep();  /* Check for RCU read-side critical section. */
+	preempt_disable();
+	ret = num_online_cpus() <= 1;
+	preempt_enable();
+	return ret;
+}
+
+/**
+ * synchronize_rcu - wait until a grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full grace
+ * period has elapsed, in other words after all currently executing RCU
+ * read-side critical sections have completed.  Note, however, that
+ * upon return from synchronize_rcu(), the caller might well be executing
+ * concurrently with new RCU read-side critical sections that began while
+ * synchronize_rcu() was waiting.  RCU read-side critical sections are
+ * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
+ * In addition, regions of code across which interrupts, preemption, or
+ * softirqs have been disabled also serve as RCU read-side critical
+ * sections.  This includes hardware interrupt handlers, softirq handlers,
+ * and NMI handlers.
+ *
+ * Note that this guarantee implies further memory-ordering guarantees.
+ * On systems with more than one CPU, when synchronize_rcu() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since
+ * the end of its last RCU read-side critical section whose beginning
+ * preceded the call to synchronize_rcu().  In addition, each CPU having
+ * an RCU read-side critical section that extends beyond the return from
+ * synchronize_rcu() is guaranteed to have executed a full memory barrier
+ * after the beginning of synchronize_rcu() and before the beginning of
+ * that RCU read-side critical section.  Note that these guarantees include
+ * CPUs that are offline, idle, or executing in user mode, as well as CPUs
+ * that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_rcu(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
+ * again only if the system has more than one CPU).
+ */
+void synchronize_rcu(void)
+{
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_rcu() in RCU read-side critical section");
+	if (rcu_blocking_is_gp())
+		return;
+	if (rcu_gp_is_expedited())
+		synchronize_rcu_expedited();
+	else
+		wait_rcu_gp(call_rcu);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
 /**
  * get_state_synchronize_rcu - Snapshot current RCU state
  *
@@ -3049,28 +3132,6 @@ static int rcu_pending(void)
 }
 
 /*
- * Return true if the specified CPU has any callback.  If all_lazy is
- * non-NULL, store an indication of whether all callbacks are lazy.
- * (If there are no callbacks, all of them are deemed to be lazy.)
- */
-static bool rcu_cpu_has_callbacks(bool *all_lazy)
-{
-	bool al = true;
-	bool hc = false;
-	struct rcu_data *rdp;
-
-	rdp = this_cpu_ptr(&rcu_data);
-	if (!rcu_segcblist_empty(&rdp->cblist)) {
-		hc = true;
-		if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist))
-			al = false;
-	}
-	if (all_lazy)
-		*all_lazy = al;
-	return hc;
-}
-
-/*
  * Helper function for rcu_barrier() tracing.  If tracing is disabled,
  * the compiler is expected to optimize this away.
  */
@@ -3299,7 +3360,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
 	trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	rcu_prepare_kthreads(cpu);
-	rcu_spawn_all_nocb_kthreads(cpu);
+	rcu_spawn_cpu_nocb_kthread(cpu);
 
 	return 0;
 }
@@ -3329,8 +3390,6 @@ int rcutree_online_cpu(unsigned int cpu)
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	rnp->ffmask |= rdp->grpmask;
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-	if (IS_ENABLED(CONFIG_TREE_SRCU))
-		srcu_online_cpu(cpu);
 	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
 		return 0; /* Too early in boot for scheduler work. */
 	sync_sched_exp_online_cleanup(cpu);
@@ -3355,8 +3414,6 @@ int rcutree_offline_cpu(unsigned int cpu)
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
 	rcutree_affinity_setting(cpu, cpu);
-	if (IS_ENABLED(CONFIG_TREE_SRCU))
-		srcu_offline_cpu(cpu);
 	return 0;
 }
 
@@ -3777,7 +3834,7 @@ void __init rcu_init(void)
 	rcu_init_one();
 	if (dump_tree)
 		rcu_dump_rcu_node_tree();
-	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+	open_softirq(RCU_SOFTIRQ, rcu_core);
 
 	/*
 	 * We don't need protection against CPU-hotplug here because
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index d90b02b53c0e..bb4f995f2d3f 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -1,25 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
  * Internal non-public definitions.
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2008
  *
  * Author: Ingo Molnar <mingo@elte.hu>
- *	   Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ *	   Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #include <linux/cache.h>
@@ -36,7 +23,6 @@
 
 /* Communicate arguments to a workqueue handler. */
 struct rcu_exp_work {
-	smp_call_func_t rew_func;
 	unsigned long rew_s;
 	struct work_struct rew_work;
 };
@@ -194,10 +180,7 @@ struct rcu_data {
 	bool rcu_need_heavy_qs;		/* GP old, so heavy quiescent state! */
 	bool rcu_urgent_qs;		/* GP old need light quiescent state. */
 #ifdef CONFIG_RCU_FAST_NO_HZ
-	bool all_lazy;			/* Are all CPU's CBs lazy? */
-	unsigned long nonlazy_posted;	/* # times non-lazy CB posted to CPU. */
-	unsigned long nonlazy_posted_snap;
-					/* Nonlazy_posted snapshot. */
+	bool all_lazy;			/* All CPU's CBs lazy at idle start? */
 	unsigned long last_accelerate;	/* Last jiffy CBs were accelerated. */
 	unsigned long last_advance_all;	/* Last jiffy CBs were all advanced. */
 	int tick_nohz_enabled_snap;	/* Previously seen value from sysfs. */
@@ -234,7 +217,13 @@ struct rcu_data {
 					/* Leader CPU takes GP-end wakeups. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 
-	/* 6) Diagnostic data, including RCU CPU stall warnings. */
+	/* 6) RCU priority boosting. */
+	struct task_struct *rcu_cpu_kthread_task;
+					/* rcuc per-CPU kthread or NULL. */
+	unsigned int rcu_cpu_kthread_status;
+	char rcu_cpu_has_work;
+
+	/* 7) Diagnostic data, including RCU CPU stall warnings. */
 	unsigned int softirq_snap;	/* Snapshot of softirq activity. */
 	/* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
 	struct irq_work rcu_iw;		/* Check for non-irq activity. */
@@ -303,6 +292,8 @@ struct rcu_state {
 	struct swait_queue_head gp_wq;		/* Where GP task waits. */
 	short gp_flags;				/* Commands for GP task. */
 	short gp_state;				/* GP kthread sleep state. */
+	unsigned long gp_wake_time;		/* Last GP kthread wake. */
+	unsigned long gp_wake_seq;		/* ->gp_seq at ^^^. */
 
 	/* End of fields guarded by root rcu_node's lock. */
 
@@ -402,13 +393,6 @@ static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
 
 int rcu_dynticks_snap(struct rcu_data *rdp);
 
-#ifdef CONFIG_RCU_BOOST
-DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
-DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
-DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
-DECLARE_PER_CPU(char, rcu_cpu_has_work);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
 /* Forward declarations for rcutree_plugin.h */
 static void rcu_bootup_announce(void);
 static void rcu_qs(void);
@@ -420,7 +404,7 @@ static void rcu_print_detail_task_stall(void);
 static int rcu_print_task_stall(struct rcu_node *rnp);
 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
-static void rcu_flavor_check_callbacks(int user);
+static void rcu_flavor_sched_clock_irq(int user);
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
@@ -431,7 +415,6 @@ static void __init rcu_spawn_boost_kthreads(void);
 static void rcu_prepare_kthreads(int cpu);
 static void rcu_cleanup_after_idle(void);
 static void rcu_prepare_for_idle(void);
-static void rcu_idle_count_callbacks_posted(void);
 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
 static void rcu_preempt_deferred_qs(struct task_struct *t);
@@ -451,7 +434,7 @@ static bool rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
 static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
-static void rcu_spawn_all_nocb_kthreads(int cpu);
+static void rcu_spawn_cpu_nocb_kthread(int cpu);
 static void __init rcu_spawn_nocb_kthreads(void);
 #ifdef CONFIG_RCU_NOCB_CPU
 static void __init rcu_organize_nocb_kthreads(void);
@@ -462,11 +445,3 @@ static void rcu_bind_gp_kthread(void);
 static bool rcu_nohz_full_cpu(void);
 static void rcu_dynticks_task_enter(void);
 static void rcu_dynticks_task_exit(void);
-
-#ifdef CONFIG_SRCU
-void srcu_online_cpu(unsigned int cpu);
-void srcu_offline_cpu(unsigned int cpu);
-#else /* #ifdef CONFIG_SRCU */
-void srcu_online_cpu(unsigned int cpu) { }
-void srcu_offline_cpu(unsigned int cpu) { }
-#endif /* #else #ifdef CONFIG_SRCU */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 928fe5893a57..4c2a0189e748 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -1,27 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * RCU expedited grace periods
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2016
  *
- * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #include <linux/lockdep.h>
 
+static void rcu_exp_handler(void *unused);
+
 /*
  * Record the start of an expedited grace period.
  */
@@ -344,7 +333,6 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 {
 	int cpu;
 	unsigned long flags;
-	smp_call_func_t func;
 	unsigned long mask_ofl_test;
 	unsigned long mask_ofl_ipi;
 	int ret;
@@ -352,7 +340,6 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 		container_of(wp, struct rcu_exp_work, rew_work);
 	struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
 
-	func = rewp->rew_func;
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 
 	/* Each pass checks a CPU for identity, offline, and idle. */
@@ -396,7 +383,7 @@ retry_ipi:
 			mask_ofl_test |= mask;
 			continue;
 		}
-		ret = smp_call_function_single(cpu, func, NULL, 0);
+		ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
 		if (!ret) {
 			mask_ofl_ipi &= ~mask;
 			continue;
@@ -426,7 +413,7 @@ retry_ipi:
  * Select the nodes that the upcoming expedited grace period needs
  * to wait for.
  */
-static void sync_rcu_exp_select_cpus(smp_call_func_t func)
+static void sync_rcu_exp_select_cpus(void)
 {
 	int cpu;
 	struct rcu_node *rnp;
@@ -440,7 +427,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func)
 		rnp->exp_need_flush = false;
 		if (!READ_ONCE(rnp->expmask))
 			continue; /* Avoid early boot non-existent wq. */
-		rnp->rew.rew_func = func;
 		if (!READ_ONCE(rcu_par_gp_wq) ||
 		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
 		    rcu_is_last_leaf_node(rnp)) {
@@ -449,7 +435,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func)
 			continue;
 		}
 		INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
-		preempt_disable();
 		cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
 		/* If all offline, queue the work on an unbound CPU. */
 		if (unlikely(cpu > rnp->grphi - rnp->grplo))
@@ -457,7 +442,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func)
 		else
 			cpu += rnp->grplo;
 		queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
-		preempt_enable();
 		rnp->exp_need_flush = true;
 	}
 
@@ -580,10 +564,10 @@ static void rcu_exp_wait_wake(unsigned long s)
  * Common code to drive an expedited grace period forward, used by
  * workqueues and mid-boot-time tasks.
  */
-static void rcu_exp_sel_wait_wake(smp_call_func_t func, unsigned long s)
+static void rcu_exp_sel_wait_wake(unsigned long s)
 {
 	/* Initialize the rcu_node tree in preparation for the wait. */
-	sync_rcu_exp_select_cpus(func);
+	sync_rcu_exp_select_cpus();
 
 	/* Wait and clean up, including waking everyone. */
 	rcu_exp_wait_wake(s);
@@ -597,52 +581,7 @@ static void wait_rcu_exp_gp(struct work_struct *wp)
 	struct rcu_exp_work *rewp;
 
 	rewp = container_of(wp, struct rcu_exp_work, rew_work);
-	rcu_exp_sel_wait_wake(rewp->rew_func, rewp->rew_s);
-}
-
-/*
- * Given a smp_call_function() handler, kick off the specified
- * implementation of expedited grace period.
- */
-static void _synchronize_rcu_expedited(smp_call_func_t func)
-{
-	struct rcu_data *rdp;
-	struct rcu_exp_work rew;
-	struct rcu_node *rnp;
-	unsigned long s;
-
-	/* If expedited grace periods are prohibited, fall back to normal. */
-	if (rcu_gp_is_normal()) {
-		wait_rcu_gp(call_rcu);
-		return;
-	}
-
-	/* Take a snapshot of the sequence number.  */
-	s = rcu_exp_gp_seq_snap();
-	if (exp_funnel_lock(s))
-		return;  /* Someone else did our work for us. */
-
-	/* Ensure that load happens before action based on it. */
-	if (unlikely(rcu_scheduler_active == RCU_SCHEDULER_INIT)) {
-		/* Direct call during scheduler init and early_initcalls(). */
-		rcu_exp_sel_wait_wake(func, s);
-	} else {
-		/* Marshall arguments & schedule the expedited grace period. */
-		rew.rew_func = func;
-		rew.rew_s = s;
-		INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
-		queue_work(rcu_gp_wq, &rew.rew_work);
-	}
-
-	/* Wait for expedited grace period to complete. */
-	rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
-	rnp = rcu_get_root();
-	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
-		   sync_exp_work_done(s));
-	smp_mb(); /* Workqueue actions happen before return. */
-
-	/* Let the next expedited grace period start. */
-	mutex_unlock(&rcu_state.exp_mutex);
+	rcu_exp_sel_wait_wake(rewp->rew_s);
 }
 
 #ifdef CONFIG_PREEMPT_RCU
@@ -654,7 +593,7 @@ static void _synchronize_rcu_expedited(smp_call_func_t func)
  * ->expmask fields in the rcu_node tree.  Otherwise, immediately
  * report the quiescent state.
  */
-static void sync_rcu_exp_handler(void *unused)
+static void rcu_exp_handler(void *unused)
 {
 	unsigned long flags;
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
@@ -697,6 +636,7 @@ static void sync_rcu_exp_handler(void *unused)
 			WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, true);
 		}
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
 	}
 
 	/*
@@ -730,43 +670,10 @@ static void sync_sched_exp_online_cleanup(int cpu)
 {
 }
 
-/**
- * synchronize_rcu_expedited - Brute-force RCU grace period
- *
- * Wait for an RCU-preempt grace period, but expedite it.  The basic
- * idea is to IPI all non-idle non-nohz online CPUs.  The IPI handler
- * checks whether the CPU is in an RCU-preempt critical section, and
- * if so, it sets a flag that causes the outermost rcu_read_unlock()
- * to report the quiescent state.  On the other hand, if the CPU is
- * not in an RCU read-side critical section, the IPI handler reports
- * the quiescent state immediately.
- *
- * Although this is a greate improvement over previous expedited
- * implementations, it is still unfriendly to real-time workloads, so is
- * thus not recommended for any sort of common-case code.  In fact, if
- * you are using synchronize_rcu_expedited() in a loop, please restructure
- * your code to batch your updates, and then Use a single synchronize_rcu()
- * instead.
- *
- * This has the same semantics as (but is more brutal than) synchronize_rcu().
- */
-void synchronize_rcu_expedited(void)
-{
-	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
-			 lock_is_held(&rcu_lock_map) ||
-			 lock_is_held(&rcu_sched_lock_map),
-			 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
-
-	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
-		return;
-	_synchronize_rcu_expedited(sync_rcu_exp_handler);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
 /* Invoked on each online non-idle CPU for expedited quiescent state. */
-static void sync_sched_exp_handler(void *unused)
+static void rcu_exp_handler(void *unused)
 {
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
@@ -798,44 +705,78 @@ static void sync_sched_exp_online_cleanup(int cpu)
 	rnp = rdp->mynode;
 	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
 		return;
-	ret = smp_call_function_single(cpu, sync_sched_exp_handler, NULL, 0);
+	ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
 	WARN_ON_ONCE(ret);
 }
 
-/*
- * Because a context switch is a grace period for !PREEMPT, any
- * blocking grace-period wait automatically implies a grace period if
- * there is only one CPU online at any point time during execution of
- * either synchronize_rcu() or synchronize_rcu_expedited().  It is OK to
- * occasionally incorrectly indicate that there are multiple CPUs online
- * when there was in fact only one the whole time, as this just adds some
- * overhead: RCU still operates correctly.
- */
-static int rcu_blocking_is_gp(void)
-{
-	int ret;
-
-	might_sleep();  /* Check for RCU read-side critical section. */
-	preempt_disable();
-	ret = num_online_cpus() <= 1;
-	preempt_enable();
-	return ret;
-}
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
-/* PREEMPT=n implementation of synchronize_rcu_expedited(). */
+/**
+ * synchronize_rcu_expedited - Brute-force RCU grace period
+ *
+ * Wait for an RCU grace period, but expedite it.  The basic idea is to
+ * IPI all non-idle non-nohz online CPUs.  The IPI handler checks whether
+ * the CPU is in an RCU critical section, and if so, it sets a flag that
+ * causes the outermost rcu_read_unlock() to report the quiescent state
+ * for RCU-preempt or asks the scheduler for help for RCU-sched.  On the
+ * other hand, if the CPU is not in an RCU read-side critical section,
+ * the IPI handler reports the quiescent state immediately.
+ *
+ * Although this is a greate improvement over previous expedited
+ * implementations, it is still unfriendly to real-time workloads, so is
+ * thus not recommended for any sort of common-case code.  In fact, if
+ * you are using synchronize_rcu_expedited() in a loop, please restructure
+ * your code to batch your updates, and then Use a single synchronize_rcu()
+ * instead.
+ *
+ * This has the same semantics as (but is more brutal than) synchronize_rcu().
+ */
 void synchronize_rcu_expedited(void)
 {
+	struct rcu_data *rdp;
+	struct rcu_exp_work rew;
+	struct rcu_node *rnp;
+	unsigned long s;
+
 	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 			 lock_is_held(&rcu_lock_map) ||
 			 lock_is_held(&rcu_sched_lock_map),
 			 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
 
-	/* If only one CPU, this is automatically a grace period. */
+	/* Is the state is such that the call is a grace period? */
 	if (rcu_blocking_is_gp())
 		return;
 
-	_synchronize_rcu_expedited(sync_sched_exp_handler);
+	/* If expedited grace periods are prohibited, fall back to normal. */
+	if (rcu_gp_is_normal()) {
+		wait_rcu_gp(call_rcu);
+		return;
+	}
+
+	/* Take a snapshot of the sequence number.  */
+	s = rcu_exp_gp_seq_snap();
+	if (exp_funnel_lock(s))
+		return;  /* Someone else did our work for us. */
+
+	/* Ensure that load happens before action based on it. */
+	if (unlikely(rcu_scheduler_active == RCU_SCHEDULER_INIT)) {
+		/* Direct call during scheduler init and early_initcalls(). */
+		rcu_exp_sel_wait_wake(s);
+	} else {
+		/* Marshall arguments & schedule the expedited grace period. */
+		rew.rew_s = s;
+		INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
+		queue_work(rcu_gp_wq, &rew.rew_work);
+	}
+
+	/* Wait for expedited grace period to complete. */
+	rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
+	rnp = rcu_get_root();
+	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
+		   sync_exp_work_done(s));
+	smp_mb(); /* Workqueue actions happen before return. */
+
+	/* Let the next expedited grace period start. */
+	mutex_unlock(&rcu_state.exp_mutex);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1b3dd2fc0cd6..97dba50f6fb2 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1,27 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
  * Internal non-public definitions that provide either classic
  * or preemptible semantics.
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright Red Hat, 2009
  * Copyright IBM Corporation, 2009
  *
  * Author: Ingo Molnar <mingo@elte.hu>
- *	   Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ *	   Paul E. McKenney <paulmck@linux.ibm.com>
  */
 
 #include <linux/delay.h>
@@ -34,17 +21,7 @@
 #include "../time/tick-internal.h"
 
 #ifdef CONFIG_RCU_BOOST
-
 #include "../locking/rtmutex_common.h"
-
-/*
- * Control variables for per-CPU and per-rcu_node kthreads.
- */
-static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
-DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
-DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
-DEFINE_PER_CPU(char, rcu_cpu_has_work);
-
 #else /* #ifdef CONFIG_RCU_BOOST */
 
 /*
@@ -307,7 +284,7 @@ static void rcu_qs(void)
 				       __this_cpu_read(rcu_data.gp_seq),
 				       TPS("cpuqs"));
 		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
-		barrier(); /* Coordinate with rcu_flavor_check_callbacks(). */
+		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
 		current->rcu_read_unlock_special.b.need_qs = false;
 	}
 }
@@ -788,13 +765,13 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 }
 
 /*
- * Check for a quiescent state from the current CPU.  When a task blocks,
- * the task is recorded in the corresponding CPU's rcu_node structure,
- * which is checked elsewhere.
- *
- * Caller must disable hard irqs.
+ * Check for a quiescent state from the current CPU, including voluntary
+ * context switches for Tasks RCU.  When a task blocks, the task is
+ * recorded in the corresponding CPU's rcu_node structure, which is checked
+ * elsewhere, hence this function need only check for quiescent states
+ * related to the current CPU, not to those related to tasks.
  */
-static void rcu_flavor_check_callbacks(int user)
+static void rcu_flavor_sched_clock_irq(int user)
 {
 	struct task_struct *t = current;
 
@@ -825,54 +802,6 @@ static void rcu_flavor_check_callbacks(int user)
 		t->rcu_read_unlock_special.b.need_qs = true;
 }
 
-/**
- * synchronize_rcu - wait until a grace period has elapsed.
- *
- * Control will return to the caller some time after a full grace
- * period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed.  Note, however, that
- * upon return from synchronize_rcu(), the caller might well be executing
- * concurrently with new RCU read-side critical sections that began while
- * synchronize_rcu() was waiting.  RCU read-side critical sections are
- * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
- * In addition, regions of code across which interrupts, preemption, or
- * softirqs have been disabled also serve as RCU read-side critical
- * sections.  This includes hardware interrupt handlers, softirq handlers,
- * and NMI handlers.
- *
- * Note that this guarantee implies further memory-ordering guarantees.
- * On systems with more than one CPU, when synchronize_rcu() returns,
- * each CPU is guaranteed to have executed a full memory barrier since
- * the end of its last RCU read-side critical section whose beginning
- * preceded the call to synchronize_rcu().  In addition, each CPU having
- * an RCU read-side critical section that extends beyond the return from
- * synchronize_rcu() is guaranteed to have executed a full memory barrier
- * after the beginning of synchronize_rcu() and before the beginning of
- * that RCU read-side critical section.  Note that these guarantees include
- * CPUs that are offline, idle, or executing in user mode, as well as CPUs
- * that are executing in the kernel.
- *
- * Furthermore, if CPU A invoked synchronize_rcu(), which returned
- * to its caller on CPU B, then both CPU A and CPU B are guaranteed
- * to have executed a full memory barrier during the execution of
- * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
- * again only if the system has more than one CPU).
- */
-void synchronize_rcu(void)
-{
-	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
-			 lock_is_held(&rcu_lock_map) ||
-			 lock_is_held(&rcu_sched_lock_map),
-			 "Illegal synchronize_rcu() in RCU read-side critical section");
-	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
-		return;
-	if (rcu_gp_is_expedited())
-		synchronize_rcu_expedited();
-	else
-		wait_rcu_gp(call_rcu);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
 /*
  * Check for a task exiting while in a preemptible-RCU read-side
  * critical section, clean up if so.  No need to issue warnings,
@@ -1088,14 +1017,10 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 }
 
 /*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context.  It is normally
- * invoked from the scheduling-clock interrupt.
+ * Check to see if this CPU is in a non-context-switch quiescent state,
+ * namely user mode and idle loop.
  */
-static void rcu_flavor_check_callbacks(int user)
+static void rcu_flavor_sched_clock_irq(int user)
 {
 	if (user || rcu_is_cpu_rrupt_from_idle()) {
 
@@ -1115,22 +1040,6 @@ static void rcu_flavor_check_callbacks(int user)
 	}
 }
 
-/* PREEMPT=n implementation of synchronize_rcu(). */
-void synchronize_rcu(void)
-{
-	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
-			 lock_is_held(&rcu_lock_map) ||
-			 lock_is_held(&rcu_sched_lock_map),
-			 "Illegal synchronize_rcu() in RCU read-side critical section");
-	if (rcu_blocking_is_gp())
-		return;
-	if (rcu_gp_is_expedited())
-		synchronize_rcu_expedited();
-	else
-		wait_rcu_gp(call_rcu);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
 /*
  * Because preemptible RCU does not exist, tasks cannot possibly exit
  * while in preemptible RCU read-side critical sections.
@@ -1307,11 +1216,11 @@ static void invoke_rcu_callbacks_kthread(void)
 	unsigned long flags;
 
 	local_irq_save(flags);
-	__this_cpu_write(rcu_cpu_has_work, 1);
-	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
-	    current != __this_cpu_read(rcu_cpu_kthread_task)) {
-		rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
-			      __this_cpu_read(rcu_cpu_kthread_status));
+	__this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
+	if (__this_cpu_read(rcu_data.rcu_cpu_kthread_task) != NULL &&
+	    current != __this_cpu_read(rcu_data.rcu_cpu_kthread_task)) {
+		rcu_wake_cond(__this_cpu_read(rcu_data.rcu_cpu_kthread_task),
+			      __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
 	}
 	local_irq_restore(flags);
 }
@@ -1322,7 +1231,7 @@ static void invoke_rcu_callbacks_kthread(void)
  */
 static bool rcu_is_callbacks_kthread(void)
 {
-	return __this_cpu_read(rcu_cpu_kthread_task) == current;
+	return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
 }
 
 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
@@ -1369,11 +1278,6 @@ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	return 0;
 }
 
-static void rcu_kthread_do_work(void)
-{
-	rcu_do_batch(this_cpu_ptr(&rcu_data));
-}
-
 static void rcu_cpu_kthread_setup(unsigned int cpu)
 {
 	struct sched_param sp;
@@ -1384,12 +1288,12 @@ static void rcu_cpu_kthread_setup(unsigned int cpu)
 
 static void rcu_cpu_kthread_park(unsigned int cpu)
 {
-	per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+	per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
 }
 
 static int rcu_cpu_kthread_should_run(unsigned int cpu)
 {
-	return __this_cpu_read(rcu_cpu_has_work);
+	return __this_cpu_read(rcu_data.rcu_cpu_has_work);
 }
 
 /*
@@ -1399,21 +1303,20 @@ static int rcu_cpu_kthread_should_run(unsigned int cpu)
  */
 static void rcu_cpu_kthread(unsigned int cpu)
 {
-	unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
-	char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
+	unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
+	char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
 	int spincnt;
 
 	for (spincnt = 0; spincnt < 10; spincnt++) {
 		trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
 		local_bh_disable();
 		*statusp = RCU_KTHREAD_RUNNING;
-		this_cpu_inc(rcu_cpu_kthread_loops);
 		local_irq_disable();
 		work = *workp;
 		*workp = 0;
 		local_irq_enable();
 		if (work)
-			rcu_kthread_do_work();
+			rcu_do_batch(this_cpu_ptr(&rcu_data));
 		local_bh_enable();
 		if (*workp == 0) {
 			trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
@@ -1459,7 +1362,7 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 }
 
 static struct smp_hotplug_thread rcu_cpu_thread_spec = {
-	.store			= &rcu_cpu_kthread_task,
+	.store			= &rcu_data.rcu_cpu_kthread_task,
 	.thread_should_run	= rcu_cpu_kthread_should_run,
 	.thread_fn		= rcu_cpu_kthread,
 	.thread_comm		= "rcuc/%u",
@@ -1476,7 +1379,7 @@ static void __init rcu_spawn_boost_kthreads(void)
 	int cpu;
 
 	for_each_possible_cpu(cpu)
-		per_cpu(rcu_cpu_has_work, cpu) = 0;
+		per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
 	if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__))
 		return;
 	rcu_for_each_leaf_node(rnp)
@@ -1543,7 +1446,7 @@ static void rcu_prepare_kthreads(int cpu)
 int rcu_needs_cpu(u64 basemono, u64 *nextevt)
 {
 	*nextevt = KTIME_MAX;
-	return rcu_cpu_has_callbacks(NULL);
+	return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist);
 }
 
 /*
@@ -1562,14 +1465,6 @@ static void rcu_prepare_for_idle(void)
 {
 }
 
-/*
- * Don't bother keeping a running count of the number of RCU callbacks
- * posted because CONFIG_RCU_FAST_NO_HZ=n.
- */
-static void rcu_idle_count_callbacks_posted(void)
-{
-}
-
 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
 
 /*
@@ -1652,11 +1547,8 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
 
 	lockdep_assert_irqs_disabled();
 
-	/* Snapshot to detect later posting of non-lazy callback. */
-	rdp->nonlazy_posted_snap = rdp->nonlazy_posted;
-
 	/* If no callbacks, RCU doesn't need the CPU. */
-	if (!rcu_cpu_has_callbacks(&rdp->all_lazy)) {
+	if (rcu_segcblist_empty(&rdp->cblist)) {
 		*nextevt = KTIME_MAX;
 		return 0;
 	}
@@ -1670,11 +1562,12 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
 	rdp->last_accelerate = jiffies;
 
 	/* Request timer delay depending on laziness, and round. */
-	if (!rdp->all_lazy) {
+	rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist);
+	if (rdp->all_lazy) {
+		dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
+	} else {
 		dj = round_up(rcu_idle_gp_delay + jiffies,
 			       rcu_idle_gp_delay) - jiffies;
-	} else {
-		dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
 	}
 	*nextevt = basemono + dj * TICK_NSEC;
 	return 0;
@@ -1704,7 +1597,7 @@ static void rcu_prepare_for_idle(void)
 	/* Handle nohz enablement switches conservatively. */
 	tne = READ_ONCE(tick_nohz_active);
 	if (tne != rdp->tick_nohz_enabled_snap) {
-		if (rcu_cpu_has_callbacks(NULL))
+		if (!rcu_segcblist_empty(&rdp->cblist))
 			invoke_rcu_core(); /* force nohz to see update. */
 		rdp->tick_nohz_enabled_snap = tne;
 		return;
@@ -1717,10 +1610,8 @@ static void rcu_prepare_for_idle(void)
 	 * callbacks, invoke RCU core for the side-effect of recalculating
 	 * idle duration on re-entry to idle.
 	 */
-	if (rdp->all_lazy &&
-	    rdp->nonlazy_posted != rdp->nonlazy_posted_snap) {
+	if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) {
 		rdp->all_lazy = false;
-		rdp->nonlazy_posted_snap = rdp->nonlazy_posted;
 		invoke_rcu_core();
 		return;
 	}
@@ -1756,19 +1647,6 @@ static void rcu_cleanup_after_idle(void)
 		invoke_rcu_core();
 }
 
-/*
- * Keep a running count of the number of non-lazy callbacks posted
- * on this CPU.  This running counter (which is never decremented) allows
- * rcu_prepare_for_idle() to detect when something out of the idle loop
- * posts a callback, even if an equal number of callbacks are invoked.
- * Of course, callbacks should only be posted from within a trace event
- * designed to be called from idle or from within RCU_NONIDLE().
- */
-static void rcu_idle_count_callbacks_posted(void)
-{
-	__this_cpu_add(rcu_data.nonlazy_posted, 1);
-}
-
 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
 
 #ifdef CONFIG_RCU_FAST_NO_HZ
@@ -1776,13 +1654,12 @@ static void rcu_idle_count_callbacks_posted(void)
 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
 {
 	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
-	unsigned long nlpd = rdp->nonlazy_posted - rdp->nonlazy_posted_snap;
 
-	sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
+	sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
 		rdp->last_accelerate & 0xffff, jiffies & 0xffff,
-		ulong2long(nlpd),
-		rdp->all_lazy ? 'L' : '.',
-		rdp->tick_nohz_enabled_snap ? '.' : 'D');
+		".l"[rdp->all_lazy],
+		".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
+		".D"[!rdp->tick_nohz_enabled_snap]);
 }
 
 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
@@ -1868,22 +1745,24 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp)
 
 /*
  * Offload callback processing from the boot-time-specified set of CPUs
- * specified by rcu_nocb_mask.  For each CPU in the set, there is a
- * kthread created that pulls the callbacks from the corresponding CPU,
- * waits for a grace period to elapse, and invokes the callbacks.
- * The no-CBs CPUs do a wake_up() on their kthread when they insert
- * a callback into any empty list, unless the rcu_nocb_poll boot parameter
- * has been specified, in which case each kthread actively polls its
- * CPU.  (Which isn't so great for energy efficiency, but which does
- * reduce RCU's overhead on that CPU.)
+ * specified by rcu_nocb_mask.  For the CPUs in the set, there are kthreads
+ * created that pull the callbacks from the corresponding CPU, wait for
+ * a grace period to elapse, and invoke the callbacks.  These kthreads
+ * are organized into leaders, which manage incoming callbacks, wait for
+ * grace periods, and awaken followers, and the followers, which only
+ * invoke callbacks.  Each leader is its own follower.  The no-CBs CPUs
+ * do a wake_up() on their kthread when they insert a callback into any
+ * empty list, unless the rcu_nocb_poll boot parameter has been specified,
+ * in which case each kthread actively polls its CPU.  (Which isn't so great
+ * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
  *
  * This is intended to be used in conjunction with Frederic Weisbecker's
  * adaptive-idle work, which would seriously reduce OS jitter on CPUs
  * running CPU-bound user-mode computations.
  *
- * Offloading of callback processing could also in theory be used as
- * an energy-efficiency measure because CPUs with no RCU callbacks
- * queued are more aggressive about entering dyntick-idle mode.
+ * Offloading of callbacks can also be used as an energy-efficiency
+ * measure because CPUs with no RCU callbacks queued are more aggressive
+ * about entering dyntick-idle mode.
  */
 
 
@@ -1987,10 +1866,7 @@ static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
 	raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 }
 
-/*
- * Does the specified CPU need an RCU callback for this invocation
- * of rcu_barrier()?
- */
+/* Does rcu_barrier need to queue an RCU callback on the specified CPU?  */
 static bool rcu_nocb_cpu_needs_barrier(int cpu)
 {
 	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
@@ -2006,8 +1882,8 @@ static bool rcu_nocb_cpu_needs_barrier(int cpu)
 	 * callbacks would be posted.  In the worst case, the first
 	 * barrier in rcu_barrier() suffices (but the caller cannot
 	 * necessarily rely on this, not a substitute for the caller
-	 * getting the concurrency design right!).  There must also be
-	 * a barrier between the following load an posting of a callback
+	 * getting the concurrency design right!).  There must also be a
+	 * barrier between the following load and posting of a callback
 	 * (if a callback is in fact needed).  This is associated with an
 	 * atomic_inc() in the caller.
 	 */
@@ -2517,9 +2393,9 @@ static void rcu_spawn_one_nocb_kthread(int cpu)
 
 /*
  * If the specified CPU is a no-CBs CPU that does not already have its
- * rcuo kthreads, spawn them.
+ * rcuo kthread, spawn it.
  */
-static void rcu_spawn_all_nocb_kthreads(int cpu)
+static void rcu_spawn_cpu_nocb_kthread(int cpu)
 {
 	if (rcu_scheduler_fully_active)
 		rcu_spawn_one_nocb_kthread(cpu);
@@ -2536,7 +2412,7 @@ static void __init rcu_spawn_nocb_kthreads(void)
 	int cpu;
 
 	for_each_online_cpu(cpu)
-		rcu_spawn_all_nocb_kthreads(cpu);
+		rcu_spawn_cpu_nocb_kthread(cpu);
 }
 
 /* How many follower CPU IDs per leader?  Default of -1 for sqrt(nr_cpu_ids). */
@@ -2670,7 +2546,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
 {
 }
 
-static void rcu_spawn_all_nocb_kthreads(int cpu)
+static void rcu_spawn_cpu_nocb_kthread(int cpu)
 {
 }
 
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 1971869c4072..e3c6395c9b4c 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -1,26 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Read-Copy Update mechanism for mutual exclusion
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, you can access it online at
- * http://www.gnu.org/licenses/gpl-2.0.html.
- *
  * Copyright IBM Corporation, 2001
  *
  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  *	    Manfred Spraul <manfred@colorfullife.com>
  *
- * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
+ * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  * Papers:
  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf