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

Pull RCU updates from Ingo Molnar:
 "This cycles's RCU changes include:

   - a couple of straggling RCU flavor consolidation updates

   - SRCU updates

   - RCU CPU stall-warning updates

   - torture-test updates

   - an LKMM commit adding support for synchronize_srcu_expedited()

   - documentation updates

   - miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (57 commits)
  net/ipv4/netfilter: Update comment from call_rcu_bh() to call_rcu()
  tools/memory-model: Add support for synchronize_srcu_expedited()
  doc/kprobes: Update obsolete RCU update functions
  torture: Suppress false-positive CONFIG_INITRAMFS_SOURCE complaint
  locktorture: NULL cxt.lwsa and cxt.lrsa to allow bad-arg detection
  rcuperf: Fix cleanup path for invalid perf_type strings
  rcutorture: Fix cleanup path for invalid torture_type strings
  rcutorture: Fix expected forward progress duration in OOM notifier
  rcutorture: Remove ->ext_irq_conflict field
  rcutorture: Make rcutorture_extend_mask() comment match the code
  tools/.../rcutorture: Convert to SPDX license identifier
  torture: Don't try to offline the last CPU
  rcu: Fix nohz status in stall warning
  rcu: Move forward-progress checkers into tree_stall.h
  rcu: Move irq-disabled stall-warning checking to tree_stall.h
  rcu: Organize functions in tree_stall.h
  rcu: Move FAST_NO_HZ stall-warning code to tree_stall.h
  rcu: Inline RCU stall-warning info helper functions
  rcu: Move rcu_print_task_exp_stall() to tree_exp.h
  rcu: Inline RCU task stall-warning helper functions
  ...

14 files changed, 831 insertions, 826 deletions

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index ad40a2617063..80a463d31a8d 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -829,7 +829,9 @@ static void lock_torture_cleanup(void)
 						"End of test: SUCCESS");
 
 	kfree(cxt.lwsa);
+	cxt.lwsa = NULL;
 	kfree(cxt.lrsa);
+	cxt.lrsa = NULL;
 
 end:
 	torture_cleanup_end();
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index acee72c0b24b..4b58c907b4b7 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -233,6 +233,7 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 #ifdef CONFIG_RCU_STALL_COMMON
 
 extern int rcu_cpu_stall_suppress;
+extern int rcu_cpu_stall_timeout;
 int rcu_jiffies_till_stall_check(void);
 
 #define rcu_ftrace_dump_stall_suppress() \
diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
index c29761152874..7a6890b23c5f 100644
--- a/kernel/rcu/rcuperf.c
+++ b/kernel/rcu/rcuperf.c
@@ -494,6 +494,10 @@ rcu_perf_cleanup(void)
 
 	if (torture_cleanup_begin())
 		return;
+	if (!cur_ops) {
+		torture_cleanup_end();
+		return;
+	}
 
 	if (reader_tasks) {
 		for (i = 0; i < nrealreaders; i++)
@@ -614,6 +618,7 @@ rcu_perf_init(void)
 		pr_cont("\n");
 		WARN_ON(!IS_MODULE(CONFIG_RCU_PERF_TEST));
 		firsterr = -EINVAL;
+		cur_ops = NULL;
 		goto unwind;
 	}
 	if (cur_ops->init)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f14d1b18a74f..efaa5b3f4d3f 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -299,7 +299,6 @@ struct rcu_torture_ops {
 	int irq_capable;
 	int can_boost;
 	int extendables;
-	int ext_irq_conflict;
 	const char *name;
 };
 
@@ -592,12 +591,7 @@ static void srcu_torture_init(void)
 
 static void srcu_torture_cleanup(void)
 {
-	static DEFINE_TORTURE_RANDOM(rand);
-
-	if (torture_random(&rand) & 0x800)
-		cleanup_srcu_struct(&srcu_ctld);
-	else
-		cleanup_srcu_struct_quiesced(&srcu_ctld);
+	cleanup_srcu_struct(&srcu_ctld);
 	srcu_ctlp = &srcu_ctl; /* In case of a later rcutorture run. */
 }
 
@@ -1160,7 +1154,7 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
 	unsigned long randmask2 = randmask1 >> 3;
 
 	WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT);
-	/* Most of the time lots of bits, half the time only one bit. */
+	/* Mostly only one bit (need preemption!), sometimes lots of bits. */
 	if (!(randmask1 & 0x7))
 		mask = mask & randmask2;
 	else
@@ -1170,10 +1164,6 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
 	    ((!(mask & RCUTORTURE_RDR_BH) && (oldmask & RCUTORTURE_RDR_BH)) ||
 	     (!(mask & RCUTORTURE_RDR_RBH) && (oldmask & RCUTORTURE_RDR_RBH))))
 		mask |= RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH;
-	if ((mask & RCUTORTURE_RDR_IRQ) &&
-	    !(mask & cur_ops->ext_irq_conflict) &&
-	    (oldmask & cur_ops->ext_irq_conflict))
-		mask |= cur_ops->ext_irq_conflict; /* Or if readers object. */
 	return mask ?: RCUTORTURE_RDR_RCU;
 }
 
@@ -1848,7 +1838,7 @@ static int rcutorture_oom_notify(struct notifier_block *self,
 	WARN(1, "%s invoked upon OOM during forward-progress testing.\n",
 	     __func__);
 	rcu_torture_fwd_cb_hist();
-	rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rcu_fwd_startat) / 2));
+	rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rcu_fwd_startat)) / 2);
 	WRITE_ONCE(rcu_fwd_emergency_stop, true);
 	smp_mb(); /* Emergency stop before free and wait to avoid hangs. */
 	pr_info("%s: Freed %lu RCU callbacks.\n",
@@ -2094,6 +2084,10 @@ rcu_torture_cleanup(void)
 			cur_ops->cb_barrier();
 		return;
 	}
+	if (!cur_ops) {
+		torture_cleanup_end();
+		return;
+	}
 
 	rcu_torture_barrier_cleanup();
 	torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);
@@ -2267,6 +2261,7 @@ rcu_torture_init(void)
 		pr_cont("\n");
 		WARN_ON(!IS_MODULE(CONFIG_RCU_TORTURE_TEST));
 		firsterr = -EINVAL;
+		cur_ops = NULL;
 		goto unwind;
 	}
 	if (cur_ops->fqs == NULL && fqs_duration != 0) {
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 5d4a39a6505a..44d6606b8325 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -76,19 +76,16 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
  * Must invoke this after you are finished using a given srcu_struct that
  * was initialized via init_srcu_struct(), else you leak memory.
  */
-void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
+void cleanup_srcu_struct(struct srcu_struct *ssp)
 {
 	WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
-	if (quiesced)
-		WARN_ON(work_pending(&ssp->srcu_work));
-	else
-		flush_work(&ssp->srcu_work);
+	flush_work(&ssp->srcu_work);
 	WARN_ON(ssp->srcu_gp_running);
 	WARN_ON(ssp->srcu_gp_waiting);
 	WARN_ON(ssp->srcu_cb_head);
 	WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
 }
-EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
 /*
  * Removes the count for the old reader from the appropriate element of
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index a60b8ba9e1ac..9b761e546de8 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -360,8 +360,14 @@ static unsigned long srcu_get_delay(struct srcu_struct *ssp)
 	return SRCU_INTERVAL;
 }
 
-/* Helper for cleanup_srcu_struct() and cleanup_srcu_struct_quiesced(). */
-void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
+/**
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @ssp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void cleanup_srcu_struct(struct srcu_struct *ssp)
 {
 	int cpu;
 
@@ -369,24 +375,14 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
 		return; /* Just leak it! */
 	if (WARN_ON(srcu_readers_active(ssp)))
 		return; /* Just leak it! */
-	if (quiesced) {
-		if (WARN_ON(delayed_work_pending(&ssp->work)))
-			return; /* Just leak it! */
-	} else {
-		flush_delayed_work(&ssp->work);
-	}
+	flush_delayed_work(&ssp->work);
 	for_each_possible_cpu(cpu) {
 		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
 
-		if (quiesced) {
-			if (WARN_ON(timer_pending(&sdp->delay_work)))
-				return; /* Just leak it! */
-			if (WARN_ON(work_pending(&sdp->work)))
-				return; /* Just leak it! */
-		} else {
-			del_timer_sync(&sdp->delay_work);
-			flush_work(&sdp->work);
-		}
+		del_timer_sync(&sdp->delay_work);
+		flush_work(&sdp->work);
+		if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
+			return; /* Forgot srcu_barrier(), so just leak it! */
 	}
 	if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
 	    WARN_ON(srcu_readers_active(ssp))) {
@@ -397,7 +393,7 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
 	free_percpu(ssp->sda);
 	ssp->sda = NULL;
 }
-EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
 /*
  * Counts the new reader in the appropriate per-CPU element of the
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 911bd9076d43..477b4eb44af5 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -52,7 +52,7 @@ void rcu_qs(void)
 	local_irq_save(flags);
 	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
 		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
-		raise_softirq(RCU_SOFTIRQ);
+		raise_softirq_irqoff(RCU_SOFTIRQ);
 	}
 	local_irq_restore(flags);
 }
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index acd6ccf56faf..ec77ec336f58 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -102,11 +102,6 @@ int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
 /* Number of rcu_nodes at specified level. */
 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
@@ -149,7 +144,7 @@ static void sync_sched_exp_online_cleanup(int cpu);
 
 /* rcuc/rcub kthread realtime priority */
 static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
-module_param(kthread_prio, int, 0644);
+module_param(kthread_prio, int, 0444);
 
 /* Delay in jiffies for grace-period initialization delays, debug only. */
 
@@ -406,7 +401,7 @@ static bool rcu_kick_kthreads;
  */
 static ulong jiffies_till_sched_qs = ULONG_MAX;
 module_param(jiffies_till_sched_qs, ulong, 0444);
-static ulong jiffies_to_sched_qs; /* Adjusted version of above if not default */
+static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
 module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
 
 /*
@@ -424,6 +419,7 @@ static void adjust_jiffies_till_sched_qs(void)
 		WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
 		return;
 	}
+	/* Otherwise, set to third fqs scan, but bound below on large system. */
 	j = READ_ONCE(jiffies_till_first_fqs) +
 		      2 * READ_ONCE(jiffies_till_next_fqs);
 	if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
@@ -513,74 +509,6 @@ static const char *gp_state_getname(short gs)
 }
 
 /*
- * Show the state of the grace-period kthreads.
- */
-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;
-	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 ? 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 %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) {
-			rdp = per_cpu_ptr(&rcu_data, cpu);
-			if (rdp->gpwrap ||
-			    ULONG_CMP_GE(rcu_state.gp_seq,
-					 rdp->gp_seq_needed))
-				continue;
-			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.
  */
 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
@@ -1034,27 +962,6 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
 }
 
 /*
- * Handler for the irq_work request posted when a grace period has
- * gone on for too long, but not yet long enough for an RCU CPU
- * stall warning.  Set state appropriately, but just complain if
- * there is unexpected state on entry.
- */
-static void rcu_iw_handler(struct irq_work *iwp)
-{
-	struct rcu_data *rdp;
-	struct rcu_node *rnp;
-
-	rdp = container_of(iwp, struct rcu_data, rcu_iw);
-	rnp = rdp->mynode;
-	raw_spin_lock_rcu_node(rnp);
-	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
-		rdp->rcu_iw_gp_seq = rnp->gp_seq;
-		rdp->rcu_iw_pending = false;
-	}
-	raw_spin_unlock_rcu_node(rnp);
-}
-
-/*
  * Return true if the specified CPU has passed through a quiescent
  * state by virtue of being in or having passed through an dynticks
  * idle state since the last call to dyntick_save_progress_counter()
@@ -1167,295 +1074,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	return 0;
 }
 
-static void record_gp_stall_check_time(void)
-{
-	unsigned long j = jiffies;
-	unsigned long j1;
-
-	rcu_state.gp_start = j;
-	j1 = rcu_jiffies_till_stall_check();
-	/* Record ->gp_start before ->jiffies_stall. */
-	smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
-	rcu_state.jiffies_resched = j + j1 / 2;
-	rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
-}
-
-/*
- * Complain about starvation of grace-period kthread.
- */
-static void rcu_check_gp_kthread_starvation(void)
-{
-	struct task_struct *gpk = rcu_state.gp_kthread;
-	unsigned long j;
-
-	j = jiffies - READ_ONCE(rcu_state.gp_activity);
-	if (j > 2 * HZ) {
-		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),
-		       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) {
-			pr_err("RCU grace-period kthread stack dump:\n");
-			sched_show_task(gpk);
-			wake_up_process(gpk);
-		}
-	}
-}
-
-/*
- * Dump stacks of all tasks running on stalled CPUs.  First try using
- * NMIs, but fall back to manual remote stack tracing on architectures
- * that don't support NMI-based stack dumps.  The NMI-triggered stack
- * traces are more accurate because they are printed by the target CPU.
- */
-static void rcu_dump_cpu_stacks(void)
-{
-	int cpu;
-	unsigned long flags;
-	struct rcu_node *rnp;
-
-	rcu_for_each_leaf_node(rnp) {
-		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-		for_each_leaf_node_possible_cpu(rnp, cpu)
-			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
-				if (!trigger_single_cpu_backtrace(cpu))
-					dump_cpu_task(cpu);
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-	}
-}
-
-/*
- * If too much time has passed in the current grace period, and if
- * so configured, go kick the relevant kthreads.
- */
-static void rcu_stall_kick_kthreads(void)
-{
-	unsigned long j;
-
-	if (!rcu_kick_kthreads)
-		return;
-	j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
-	if (time_after(jiffies, j) && rcu_state.gp_kthread &&
-	    (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
-		WARN_ONCE(1, "Kicking %s grace-period kthread\n",
-			  rcu_state.name);
-		rcu_ftrace_dump(DUMP_ALL);
-		wake_up_process(rcu_state.gp_kthread);
-		WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
-	}
-}
-
-static void panic_on_rcu_stall(void)
-{
-	if (sysctl_panic_on_rcu_stall)
-		panic("RCU Stall\n");
-}
-
-static void print_other_cpu_stall(unsigned long gp_seq)
-{
-	int cpu;
-	unsigned long flags;
-	unsigned long gpa;
-	unsigned long j;
-	int ndetected = 0;
-	struct rcu_node *rnp = rcu_get_root();
-	long totqlen = 0;
-
-	/* Kick and suppress, if so configured. */
-	rcu_stall_kick_kthreads();
-	if (rcu_cpu_stall_suppress)
-		return;
-
-	/*
-	 * OK, time to rat on our buddy...
-	 * See Documentation/RCU/stallwarn.txt for info on how to debug
-	 * RCU CPU stall warnings.
-	 */
-	pr_err("INFO: %s detected stalls on CPUs/tasks:", rcu_state.name);
-	print_cpu_stall_info_begin();
-	rcu_for_each_leaf_node(rnp) {
-		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-		ndetected += rcu_print_task_stall(rnp);
-		if (rnp->qsmask != 0) {
-			for_each_leaf_node_possible_cpu(rnp, cpu)
-				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
-					print_cpu_stall_info(cpu);
-					ndetected++;
-				}
-		}
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-	}
-
-	print_cpu_stall_info_end();
-	for_each_possible_cpu(cpu)
-		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
-	       smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
-	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
-	if (ndetected) {
-		rcu_dump_cpu_stacks();
-
-		/* Complain about tasks blocking the grace period. */
-		rcu_print_detail_task_stall();
-	} else {
-		if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
-			pr_err("INFO: Stall ended before state dump start\n");
-		} else {
-			j = jiffies;
-			gpa = READ_ONCE(rcu_state.gp_activity);
-			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
-			       rcu_state.name, j - gpa, j, gpa,
-			       READ_ONCE(jiffies_till_next_fqs),
-			       rcu_get_root()->qsmask);
-			/* In this case, the current CPU might be at fault. */
-			sched_show_task(current);
-		}
-	}
-	/* Rewrite if needed in case of slow consoles. */
-	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
-		WRITE_ONCE(rcu_state.jiffies_stall,
-			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
-
-	rcu_check_gp_kthread_starvation();
-
-	panic_on_rcu_stall();
-
-	rcu_force_quiescent_state();  /* Kick them all. */
-}
-
-static void print_cpu_stall(void)
-{
-	int cpu;
-	unsigned long flags;
-	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
-	struct rcu_node *rnp = rcu_get_root();
-	long totqlen = 0;
-
-	/* Kick and suppress, if so configured. */
-	rcu_stall_kick_kthreads();
-	if (rcu_cpu_stall_suppress)
-		return;
-
-	/*
-	 * OK, time to rat on ourselves...
-	 * See Documentation/RCU/stallwarn.txt for info on how to debug
-	 * RCU CPU stall warnings.
-	 */
-	pr_err("INFO: %s self-detected stall on CPU", rcu_state.name);
-	print_cpu_stall_info_begin();
-	raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
-	print_cpu_stall_info(smp_processor_id());
-	raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
-	print_cpu_stall_info_end();
-	for_each_possible_cpu(cpu)
-		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n",
-		jiffies - rcu_state.gp_start,
-		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
-
-	rcu_check_gp_kthread_starvation();
-
-	rcu_dump_cpu_stacks();
-
-	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	/* Rewrite if needed in case of slow consoles. */
-	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
-		WRITE_ONCE(rcu_state.jiffies_stall,
-			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
-	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
-	panic_on_rcu_stall();
-
-	/*
-	 * Attempt to revive the RCU machinery by forcing a context switch.
-	 *
-	 * A context switch would normally allow the RCU state machine to make
-	 * progress and it could be we're stuck in kernel space without context
-	 * switches for an entirely unreasonable amount of time.
-	 */
-	set_tsk_need_resched(current);
-	set_preempt_need_resched();
-}
-
-static void check_cpu_stall(struct rcu_data *rdp)
-{
-	unsigned long gs1;
-	unsigned long gs2;
-	unsigned long gps;
-	unsigned long j;
-	unsigned long jn;
-	unsigned long js;
-	struct rcu_node *rnp;
-
-	if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
-	    !rcu_gp_in_progress())
-		return;
-	rcu_stall_kick_kthreads();
-	j = jiffies;
-
-	/*
-	 * Lots of memory barriers to reject false positives.
-	 *
-	 * The idea is to pick up rcu_state.gp_seq, then
-	 * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
-	 * another copy of rcu_state.gp_seq.  These values are updated in
-	 * the opposite order with memory barriers (or equivalent) during
-	 * grace-period initialization and cleanup.  Now, a false positive
-	 * can occur if we get an new value of rcu_state.gp_start and a old
-	 * value of rcu_state.jiffies_stall.  But given the memory barriers,
-	 * the only way that this can happen is if one grace period ends
-	 * and another starts between these two fetches.  This is detected
-	 * by comparing the second fetch of rcu_state.gp_seq with the
-	 * previous fetch from rcu_state.gp_seq.
-	 *
-	 * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
-	 * and rcu_state.gp_start suffice to forestall false positives.
-	 */
-	gs1 = READ_ONCE(rcu_state.gp_seq);
-	smp_rmb(); /* Pick up ->gp_seq first... */
-	js = READ_ONCE(rcu_state.jiffies_stall);
-	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
-	gps = READ_ONCE(rcu_state.gp_start);
-	smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
-	gs2 = READ_ONCE(rcu_state.gp_seq);
-	if (gs1 != gs2 ||
-	    ULONG_CMP_LT(j, js) ||
-	    ULONG_CMP_GE(gps, js))
-		return; /* No stall or GP completed since entering function. */
-	rnp = rdp->mynode;
-	jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
-	if (rcu_gp_in_progress() &&
-	    (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
-	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
-
-		/* We haven't checked in, so go dump stack. */
-		print_cpu_stall();
-
-	} else if (rcu_gp_in_progress() &&
-		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
-		   cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
-
-		/* They had a few time units to dump stack, so complain. */
-		print_other_cpu_stall(gs2);
-	}
-}
-
-/**
- * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
- *
- * Set the stall-warning timeout way off into the future, thus preventing
- * any RCU CPU stall-warning messages from appearing in the current set of
- * RCU grace periods.
- *
- * The caller must disable hard irqs.
- */
-void rcu_cpu_stall_reset(void)
-{
-	WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
-}
-
 /* Trace-event wrapper function for trace_rcu_future_grace_period.  */
 static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
 			      unsigned long gp_seq_req, const char *s)
@@ -1585,7 +1203,7 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
 static void rcu_gp_kthread_wake(void)
 {
 	if ((current == rcu_state.gp_kthread &&
-	     !in_interrupt() && !in_serving_softirq()) ||
+	     !in_irq() && !in_serving_softirq()) ||
 	    !READ_ONCE(rcu_state.gp_flags) ||
 	    !rcu_state.gp_kthread)
 		return;
@@ -2295,11 +1913,10 @@ rcu_report_qs_rdp(int cpu, struct rcu_data *rdp)
 		return;
 	}
 	mask = rdp->grpmask;
+	rdp->core_needs_qs = false;
 	if ((rnp->qsmask & mask) == 0) {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	} else {
-		rdp->core_needs_qs = false;
-
 		/*
 		 * This GP can't end until cpu checks in, so all of our
 		 * callbacks can be processed during the next GP.
@@ -2548,11 +2165,11 @@ void rcu_sched_clock_irq(int user)
 }
 
 /*
- * Scan the leaf rcu_node structures, processing dyntick state for any that
- * have not yet encountered a quiescent state, using the function specified.
- * Also initiate boosting for any threads blocked on the root rcu_node.
- *
- * The caller must have suppressed start of new grace periods.
+ * Scan the leaf rcu_node structures.  For each structure on which all
+ * CPUs have reported a quiescent state and on which there are tasks
+ * blocking the current grace period, initiate RCU priority boosting.
+ * Otherwise, invoke the specified function to check dyntick state for
+ * each CPU that has not yet reported a quiescent state.
  */
 static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 {
@@ -2635,101 +2252,6 @@ void rcu_force_quiescent_state(void)
 }
 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 
-/*
- * This function checks for grace-period requests that fail to motivate
- * RCU to come out of its idle mode.
- */
-void
-rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
-			 const unsigned long gpssdelay)
-{
-	unsigned long flags;
-	unsigned long j;
-	struct rcu_node *rnp_root = rcu_get_root();
-	static atomic_t warned = ATOMIC_INIT(0);
-
-	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
-	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
-		return;
-	j = jiffies; /* Expensive access, and in common case don't get here. */
-	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
-	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
-	    atomic_read(&warned))
-		return;
-
-	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	j = jiffies;
-	if (rcu_gp_in_progress() ||
-	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
-	    time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
-	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
-	    atomic_read(&warned)) {
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-		return;
-	}
-	/* Hold onto the leaf lock to make others see warned==1. */
-
-	if (rnp_root != rnp)
-		raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
-	j = jiffies;
-	if (rcu_gp_in_progress() ||
-	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
-	    time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
-	    time_before(j, rcu_state.gp_activity + gpssdelay) ||
-	    atomic_xchg(&warned, 1)) {
-		raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-		return;
-	}
-	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();
-}
-
-/*
- * Do a forward-progress check for rcutorture.  This is normally invoked
- * due to an OOM event.  The argument "j" gives the time period during
- * which rcutorture would like progress to have been made.
- */
-void rcu_fwd_progress_check(unsigned long j)
-{
-	unsigned long cbs;
-	int cpu;
-	unsigned long max_cbs = 0;
-	int max_cpu = -1;
-	struct rcu_data *rdp;
-
-	if (rcu_gp_in_progress()) {
-		pr_info("%s: GP age %lu jiffies\n",
-			__func__, jiffies - rcu_state.gp_start);
-		show_rcu_gp_kthreads();
-	} else {
-		pr_info("%s: Last GP end %lu jiffies ago\n",
-			__func__, jiffies - rcu_state.gp_end);
-		preempt_disable();
-		rdp = this_cpu_ptr(&rcu_data);
-		rcu_check_gp_start_stall(rdp->mynode, rdp, j);
-		preempt_enable();
-	}
-	for_each_possible_cpu(cpu) {
-		cbs = rcu_get_n_cbs_cpu(cpu);
-		if (!cbs)
-			continue;
-		if (max_cpu < 0)
-			pr_info("%s: callbacks", __func__);
-		pr_cont(" %d: %lu", cpu, cbs);
-		if (cbs <= max_cbs)
-			continue;
-		max_cbs = cbs;
-		max_cpu = cpu;
-	}
-	if (max_cpu >= 0)
-		pr_cont("\n");
-}
-EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
-
 /* Perform RCU core processing work for the current CPU.  */
 static __latent_entropy void rcu_core(struct softirq_action *unused)
 {
@@ -3559,13 +3081,11 @@ static int rcu_pm_notify(struct notifier_block *self,
 	switch (action) {
 	case PM_HIBERNATION_PREPARE:
 	case PM_SUSPEND_PREPARE:
-		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
-			rcu_expedite_gp();
+		rcu_expedite_gp();
 		break;
 	case PM_POST_HIBERNATION:
 	case PM_POST_SUSPEND:
-		if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
-			rcu_unexpedite_gp();
+		rcu_unexpedite_gp();
 		break;
 	default:
 		break;
@@ -3742,8 +3262,7 @@ static void __init rcu_init_geometry(void)
 		jiffies_till_first_fqs = d;
 	if (jiffies_till_next_fqs == ULONG_MAX)
 		jiffies_till_next_fqs = d;
-	if (jiffies_till_sched_qs == ULONG_MAX)
-		adjust_jiffies_till_sched_qs();
+	adjust_jiffies_till_sched_qs();
 
 	/* If the compile-time values are accurate, just leave. */
 	if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
@@ -3858,5 +3377,6 @@ void __init rcu_init(void)
 	srcu_init();
 }
 
+#include "tree_stall.h"
 #include "tree_exp.h"
 #include "tree_plugin.h"
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index bb4f995f2d3f..e253d11af3c4 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -393,15 +393,13 @@ static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
 
 int rcu_dynticks_snap(struct rcu_data *rdp);
 
-/* Forward declarations for rcutree_plugin.h */
+/* Forward declarations for tree_plugin.h */
 static void rcu_bootup_announce(void);
 static void rcu_qs(void);
 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
 #ifdef CONFIG_HOTPLUG_CPU
 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
-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_sched_clock_irq(int user);
@@ -418,9 +416,6 @@ static void rcu_prepare_for_idle(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);
-static void print_cpu_stall_info_begin(void);
-static void print_cpu_stall_info(int cpu);
-static void print_cpu_stall_info_end(void);
 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
 static bool rcu_nocb_cpu_needs_barrier(int cpu);
 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
@@ -445,3 +440,10 @@ 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);
+
+/* Forward declarations for tree_stall.h */
+static void record_gp_stall_check_time(void);
+static void rcu_iw_handler(struct irq_work *iwp);
+static void check_cpu_stall(struct rcu_data *rdp);
+static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
+				     const unsigned long gpssdelay);
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 4c2a0189e748..9c990df880d1 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -10,6 +10,7 @@
 #include <linux/lockdep.h>
 
 static void rcu_exp_handler(void *unused);
+static int rcu_print_task_exp_stall(struct rcu_node *rnp);
 
 /*
  * Record the start of an expedited grace period.
@@ -633,7 +634,7 @@ static void rcu_exp_handler(void *unused)
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		if (rnp->expmask & rdp->grpmask) {
 			rdp->deferred_qs = true;
-			WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, true);
+			t->rcu_read_unlock_special.b.exp_hint = true;
 		}
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
@@ -648,7 +649,7 @@ static void rcu_exp_handler(void *unused)
 	 *
 	 * If the CPU is fully enabled (or if some buggy RCU-preempt
 	 * read-side critical section is being used from idle), just
-	 * invoke rcu_preempt_defer_qs() to immediately report the
+	 * invoke rcu_preempt_deferred_qs() to immediately report the
 	 * quiescent state.  We cannot use rcu_read_unlock_special()
 	 * because we are in an interrupt handler, which will cause that
 	 * function to take an early exit without doing anything.
@@ -670,6 +671,27 @@ static void sync_sched_exp_online_cleanup(int cpu)
 {
 }
 
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each that is blocking the current
+ * expedited grace period.
+ */
+static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+{
+	struct task_struct *t;
+	int ndetected = 0;
+
+	if (!rnp->exp_tasks)
+		return 0;
+	t = list_entry(rnp->exp_tasks->prev,
+		       struct task_struct, rcu_node_entry);
+	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+		pr_cont(" P%d", t->pid);
+		ndetected++;
+	}
+	return ndetected;
+}
+
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
 /* Invoked on each online non-idle CPU for expedited quiescent state. */
@@ -709,6 +731,16 @@ static void sync_sched_exp_online_cleanup(int cpu)
 	WARN_ON_ONCE(ret);
 }
 
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections that are
+ * blocking the current expedited grace period.
+ */
+static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+{
+	return 0;
+}
+
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 /**
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 97dba50f6fb2..1102765f91fd 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -285,7 +285,7 @@ static void rcu_qs(void)
 				       TPS("cpuqs"));
 		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
 		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
-		current->rcu_read_unlock_special.b.need_qs = false;
+		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
 	}
 }
 
@@ -643,100 +643,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
 }
 
 /*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period on the specified rcu_node structure.
- */
-static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
-{
-	unsigned long flags;
-	struct task_struct *t;
-
-	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	if (!rcu_preempt_blocked_readers_cgp(rnp)) {
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-		return;
-	}
-	t = list_entry(rnp->gp_tasks->prev,
-		       struct task_struct, rcu_node_entry);
-	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
-		/*
-		 * We could be printing a lot while holding a spinlock.
-		 * Avoid triggering hard lockup.
-		 */
-		touch_nmi_watchdog();
-		sched_show_task(t);
-	}
-	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-}
-
-/*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period.
- */
-static void rcu_print_detail_task_stall(void)
-{
-	struct rcu_node *rnp = rcu_get_root();
-
-	rcu_print_detail_task_stall_rnp(rnp);
-	rcu_for_each_leaf_node(rnp)
-		rcu_print_detail_task_stall_rnp(rnp);
-}
-
-static void rcu_print_task_stall_begin(struct rcu_node *rnp)
-{
-	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
-	       rnp->level, rnp->grplo, rnp->grphi);
-}
-
-static void rcu_print_task_stall_end(void)
-{
-	pr_cont("\n");
-}
-
-/*
- * Scan the current list of tasks blocked within RCU read-side critical
- * sections, printing out the tid of each.
- */
-static int rcu_print_task_stall(struct rcu_node *rnp)
-{
-	struct task_struct *t;
-	int ndetected = 0;
-
-	if (!rcu_preempt_blocked_readers_cgp(rnp))
-		return 0;
-	rcu_print_task_stall_begin(rnp);
-	t = list_entry(rnp->gp_tasks->prev,
-		       struct task_struct, rcu_node_entry);
-	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
-		pr_cont(" P%d", t->pid);
-		ndetected++;
-	}
-	rcu_print_task_stall_end();
-	return ndetected;
-}
-
-/*
- * Scan the current list of tasks blocked within RCU read-side critical
- * sections, printing out the tid of each that is blocking the current
- * expedited grace period.
- */
-static int rcu_print_task_exp_stall(struct rcu_node *rnp)
-{
-	struct task_struct *t;
-	int ndetected = 0;
-
-	if (!rnp->exp_tasks)
-		return 0;
-	t = list_entry(rnp->exp_tasks->prev,
-		       struct task_struct, rcu_node_entry);
-	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
-		pr_cont(" P%d", t->pid);
-		ndetected++;
-	}
-	return ndetected;
-}
-
-/*
  * Check that the list of blocked tasks for the newly completed grace
  * period is in fact empty.  It is a serious bug to complete a grace
  * period that still has RCU readers blocked!  This function must be
@@ -804,19 +710,25 @@ static void rcu_flavor_sched_clock_irq(int user)
 
 /*
  * Check for a task exiting while in a preemptible-RCU read-side
- * critical section, clean up if so.  No need to issue warnings,
- * as debug_check_no_locks_held() already does this if lockdep
- * is enabled.
+ * critical section, clean up if so.  No need to issue warnings, as
+ * debug_check_no_locks_held() already does this if lockdep is enabled.
+ * Besides, if this function does anything other than just immediately
+ * return, there was a bug of some sort.  Spewing warnings from this
+ * function is like as not to simply obscure important prior warnings.
  */
 void exit_rcu(void)
 {
 	struct task_struct *t = current;
 
-	if (likely(list_empty(&current->rcu_node_entry)))
+	if (unlikely(!list_empty(&current->rcu_node_entry))) {
+		t->rcu_read_lock_nesting = 1;
+		barrier();
+		WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
+	} else if (unlikely(t->rcu_read_lock_nesting)) {
+		t->rcu_read_lock_nesting = 1;
+	} else {
 		return;
-	t->rcu_read_lock_nesting = 1;
-	barrier();
-	t->rcu_read_unlock_special.b.blocked = true;
+	}
 	__rcu_read_unlock();
 	rcu_preempt_deferred_qs(current);
 }
@@ -980,33 +892,6 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 static void rcu_preempt_deferred_qs(struct task_struct *t) { }
 
 /*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections.
- */
-static void rcu_print_detail_task_stall(void)
-{
-}
-
-/*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections.
- */
-static int rcu_print_task_stall(struct rcu_node *rnp)
-{
-	return 0;
-}
-
-/*
- * Because preemptible RCU does not exist, we never have to check for
- * tasks blocked within RCU read-side critical sections that are
- * blocking the current expedited grace period.
- */
-static int rcu_print_task_exp_stall(struct rcu_node *rnp)
-{
-	return 0;
-}
-
-/*
  * Because there is no preemptible RCU, there can be no readers blocked,
  * so there is no need to check for blocked tasks.  So check only for
  * bogus qsmask values.
@@ -1185,8 +1070,6 @@ static int rcu_boost_kthread(void *arg)
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 	__releases(rnp->lock)
 {
-	struct task_struct *t;
-
 	raw_lockdep_assert_held_rcu_node(rnp);
 	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@@ -1200,9 +1083,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 		if (rnp->exp_tasks == NULL)
 			rnp->boost_tasks = rnp->gp_tasks;
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-		t = rnp->boost_kthread_task;
-		if (t)
-			rcu_wake_cond(t, rnp->boost_kthread_status);
+		rcu_wake_cond(rnp->boost_kthread_task,
+			      rnp->boost_kthread_status);
 	} else {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
@@ -1649,98 +1531,6 @@ static void rcu_cleanup_after_idle(void)
 
 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
 
-#ifdef CONFIG_RCU_FAST_NO_HZ
-
-static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
-{
-	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
-
-	sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
-		rdp->last_accelerate & 0xffff, jiffies & 0xffff,
-		".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 */
-
-static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
-{
-	*cp = '\0';
-}
-
-#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
-
-/* Initiate the stall-info list. */
-static void print_cpu_stall_info_begin(void)
-{
-	pr_cont("\n");
-}
-
-/*
- * Print out diagnostic information for the specified stalled CPU.
- *
- * If the specified CPU is aware of the current RCU grace period, then
- * print the number of scheduling clock interrupts the CPU has taken
- * during the time that it has been aware.  Otherwise, print the number
- * of RCU grace periods that this CPU is ignorant of, for example, "1"
- * if the CPU was aware of the previous grace period.
- *
- * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
- */
-static void print_cpu_stall_info(int cpu)
-{
-	unsigned long delta;
-	char fast_no_hz[72];
-	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
-	char *ticks_title;
-	unsigned long ticks_value;
-
-	/*
-	 * We could be printing a lot while holding a spinlock.  Avoid
-	 * triggering hard lockup.
-	 */
-	touch_nmi_watchdog();
-
-	ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
-	if (ticks_value) {
-		ticks_title = "GPs behind";
-	} else {
-		ticks_title = "ticks this GP";
-		ticks_value = rdp->ticks_this_gp;
-	}
-	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
-	delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
-	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
-	       cpu,
-	       "O."[!!cpu_online(cpu)],
-	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
-	       "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
-	       !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
-			rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
-				"!."[!delta],
-	       ticks_value, ticks_title,
-	       rcu_dynticks_snap(rdp) & 0xfff,
-	       rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
-	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
-	       READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
-	       fast_no_hz);
-}
-
-/* Terminate the stall-info list. */
-static void print_cpu_stall_info_end(void)
-{
-	pr_err("\t");
-}
-
-/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
-static void zero_cpu_stall_ticks(struct rcu_data *rdp)
-{
-	rdp->ticks_this_gp = 0;
-	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
-	WRITE_ONCE(rdp->last_fqs_resched, jiffies);
-}
-
 #ifdef CONFIG_RCU_NOCB_CPU
 
 /*
@@ -1766,11 +1556,22 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp)
  */
 
 
-/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
+/*
+ * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
+ * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
+ * comma-separated list of CPUs and/or CPU ranges.  If an invalid list is
+ * given, a warning is emitted and all CPUs are offloaded.
+ */
 static int __init rcu_nocb_setup(char *str)
 {
 	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
-	cpulist_parse(str, rcu_nocb_mask);
+	if (!strcasecmp(str, "all"))
+		cpumask_setall(rcu_nocb_mask);
+	else
+		if (cpulist_parse(str, rcu_nocb_mask)) {
+			pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
+			cpumask_setall(rcu_nocb_mask);
+		}
 	return 1;
 }
 __setup("rcu_nocbs=", rcu_nocb_setup);
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
new file mode 100644
index 000000000000..f65a73a97323
--- /dev/null
+++ b/kernel/rcu/tree_stall.h
@@ -0,0 +1,709 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * RCU CPU stall warnings for normal RCU grace periods
+ *
+ * Copyright IBM Corporation, 2019
+ *
+ * Author: Paul E. McKenney <paulmck@linux.ibm.com>
+ */
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Controlling CPU stall warnings, including delay calculation.
+
+/* panic() on RCU Stall sysctl. */
+int sysctl_panic_on_rcu_stall __read_mostly;
+
+#ifdef CONFIG_PROVE_RCU
+#define RCU_STALL_DELAY_DELTA	       (5 * HZ)
+#else
+#define RCU_STALL_DELAY_DELTA	       0
+#endif
+
+/* Limit-check stall timeouts specified at boottime and runtime. */
+int rcu_jiffies_till_stall_check(void)
+{
+	int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
+
+	/*
+	 * Limit check must be consistent with the Kconfig limits
+	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
+	 */
+	if (till_stall_check < 3) {
+		WRITE_ONCE(rcu_cpu_stall_timeout, 3);
+		till_stall_check = 3;
+	} else if (till_stall_check > 300) {
+		WRITE_ONCE(rcu_cpu_stall_timeout, 300);
+		till_stall_check = 300;
+	}
+	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
+}
+EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
+
+/* Don't do RCU CPU stall warnings during long sysrq printouts. */
+void rcu_sysrq_start(void)
+{
+	if (!rcu_cpu_stall_suppress)
+		rcu_cpu_stall_suppress = 2;
+}
+
+void rcu_sysrq_end(void)
+{
+	if (rcu_cpu_stall_suppress == 2)
+		rcu_cpu_stall_suppress = 0;
+}
+
+/* Don't print RCU CPU stall warnings during a kernel panic. */
+static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
+{
+	rcu_cpu_stall_suppress = 1;
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block rcu_panic_block = {
+	.notifier_call = rcu_panic,
+};
+
+static int __init check_cpu_stall_init(void)
+{
+	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
+	return 0;
+}
+early_initcall(check_cpu_stall_init);
+
+/* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
+static void panic_on_rcu_stall(void)
+{
+	if (sysctl_panic_on_rcu_stall)
+		panic("RCU Stall\n");
+}
+
+/**
+ * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
+ *
+ * Set the stall-warning timeout way off into the future, thus preventing
+ * any RCU CPU stall-warning messages from appearing in the current set of
+ * RCU grace periods.
+ *
+ * The caller must disable hard irqs.
+ */
+void rcu_cpu_stall_reset(void)
+{
+	WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Interaction with RCU grace periods
+
+/* Start of new grace period, so record stall time (and forcing times). */
+static void record_gp_stall_check_time(void)
+{
+	unsigned long j = jiffies;
+	unsigned long j1;
+
+	rcu_state.gp_start = j;
+	j1 = rcu_jiffies_till_stall_check();
+	/* Record ->gp_start before ->jiffies_stall. */
+	smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
+	rcu_state.jiffies_resched = j + j1 / 2;
+	rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
+}
+
+/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+	rdp->ticks_this_gp = 0;
+	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
+	WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+}
+
+/*
+ * If too much time has passed in the current grace period, and if
+ * so configured, go kick the relevant kthreads.
+ */
+static void rcu_stall_kick_kthreads(void)
+{
+	unsigned long j;
+
+	if (!rcu_kick_kthreads)
+		return;
+	j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
+	if (time_after(jiffies, j) && rcu_state.gp_kthread &&
+	    (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
+		WARN_ONCE(1, "Kicking %s grace-period kthread\n",
+			  rcu_state.name);
+		rcu_ftrace_dump(DUMP_ALL);
+		wake_up_process(rcu_state.gp_kthread);
+		WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
+	}
+}
+
+/*
+ * Handler for the irq_work request posted about halfway into the RCU CPU
+ * stall timeout, and used to detect excessive irq disabling.  Set state
+ * appropriately, but just complain if there is unexpected state on entry.
+ */
+static void rcu_iw_handler(struct irq_work *iwp)
+{
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+
+	rdp = container_of(iwp, struct rcu_data, rcu_iw);
+	rnp = rdp->mynode;
+	raw_spin_lock_rcu_node(rnp);
+	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
+		rdp->rcu_iw_gp_seq = rnp->gp_seq;
+		rdp->rcu_iw_pending = false;
+	}
+	raw_spin_unlock_rcu_node(rnp);
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Printing RCU CPU stall warnings
+
+#ifdef CONFIG_PREEMPT
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period on the specified rcu_node structure.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	struct task_struct *t;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	t = list_entry(rnp->gp_tasks->prev,
+		       struct task_struct, rcu_node_entry);
+	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+		/*
+		 * We could be printing a lot while holding a spinlock.
+		 * Avoid triggering hard lockup.
+		 */
+		touch_nmi_watchdog();
+		sched_show_task(t);
+	}
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+	struct task_struct *t;
+	int ndetected = 0;
+
+	if (!rcu_preempt_blocked_readers_cgp(rnp))
+		return 0;
+	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+	       rnp->level, rnp->grplo, rnp->grphi);
+	t = list_entry(rnp->gp_tasks->prev,
+		       struct task_struct, rcu_node_entry);
+	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+		pr_cont(" P%d", t->pid);
+		ndetected++;
+	}
+	pr_cont("\n");
+	return ndetected;
+}
+
+#else /* #ifdef CONFIG_PREEMPT */
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+	return 0;
+}
+#endif /* #else #ifdef CONFIG_PREEMPT */
+
+/*
+ * Dump stacks of all tasks running on stalled CPUs.  First try using
+ * NMIs, but fall back to manual remote stack tracing on architectures
+ * that don't support NMI-based stack dumps.  The NMI-triggered stack
+ * traces are more accurate because they are printed by the target CPU.
+ */
+static void rcu_dump_cpu_stacks(void)
+{
+	int cpu;
+	unsigned long flags;
+	struct rcu_node *rnp;
+
+	rcu_for_each_leaf_node(rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		for_each_leaf_node_possible_cpu(rnp, cpu)
+			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
+				if (!trigger_single_cpu_backtrace(cpu))
+					dump_cpu_task(cpu);
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+}
+
+#ifdef CONFIG_RCU_FAST_NO_HZ
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+
+	sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
+		rdp->last_accelerate & 0xffff, jiffies & 0xffff,
+		".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 */
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+	*cp = '\0';
+}
+
+#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+/*
+ * Print out diagnostic information for the specified stalled CPU.
+ *
+ * If the specified CPU is aware of the current RCU grace period, then
+ * print the number of scheduling clock interrupts the CPU has taken
+ * during the time that it has been aware.  Otherwise, print the number
+ * of RCU grace periods that this CPU is ignorant of, for example, "1"
+ * if the CPU was aware of the previous grace period.
+ *
+ * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
+ */
+static void print_cpu_stall_info(int cpu)
+{
+	unsigned long delta;
+	char fast_no_hz[72];
+	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+	char *ticks_title;
+	unsigned long ticks_value;
+
+	/*
+	 * We could be printing a lot while holding a spinlock.  Avoid
+	 * triggering hard lockup.
+	 */
+	touch_nmi_watchdog();
+
+	ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
+	if (ticks_value) {
+		ticks_title = "GPs behind";
+	} else {
+		ticks_title = "ticks this GP";
+		ticks_value = rdp->ticks_this_gp;
+	}
+	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
+	delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
+	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
+	       cpu,
+	       "O."[!!cpu_online(cpu)],
+	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
+	       "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
+	       !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
+			rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
+				"!."[!delta],
+	       ticks_value, ticks_title,
+	       rcu_dynticks_snap(rdp) & 0xfff,
+	       rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
+	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+	       READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
+	       fast_no_hz);
+}
+
+/* Complain about starvation of grace-period kthread.  */
+static void rcu_check_gp_kthread_starvation(void)
+{
+	struct task_struct *gpk = rcu_state.gp_kthread;
+	unsigned long j;
+
+	j = jiffies - READ_ONCE(rcu_state.gp_activity);
+	if (j > 2 * HZ) {
+		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),
+		       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) {
+			pr_err("RCU grace-period kthread stack dump:\n");
+			sched_show_task(gpk);
+			wake_up_process(gpk);
+		}
+	}
+}
+
+static void print_other_cpu_stall(unsigned long gp_seq)
+{
+	int cpu;
+	unsigned long flags;
+	unsigned long gpa;
+	unsigned long j;
+	int ndetected = 0;
+	struct rcu_node *rnp;
+	long totqlen = 0;
+
+	/* Kick and suppress, if so configured. */
+	rcu_stall_kick_kthreads();
+	if (rcu_cpu_stall_suppress)
+		return;
+
+	/*
+	 * OK, time to rat on our buddy...
+	 * See Documentation/RCU/stallwarn.txt for info on how to debug
+	 * RCU CPU stall warnings.
+	 */
+	pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
+	rcu_for_each_leaf_node(rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		ndetected += rcu_print_task_stall(rnp);
+		if (rnp->qsmask != 0) {
+			for_each_leaf_node_possible_cpu(rnp, cpu)
+				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+					print_cpu_stall_info(cpu);
+					ndetected++;
+				}
+		}
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+
+	for_each_possible_cpu(cpu)
+		totqlen += rcu_get_n_cbs_cpu(cpu);
+	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
+	       smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
+	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
+	if (ndetected) {
+		rcu_dump_cpu_stacks();
+
+		/* Complain about tasks blocking the grace period. */
+		rcu_for_each_leaf_node(rnp)
+			rcu_print_detail_task_stall_rnp(rnp);
+	} else {
+		if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
+			pr_err("INFO: Stall ended before state dump start\n");
+		} else {
+			j = jiffies;
+			gpa = READ_ONCE(rcu_state.gp_activity);
+			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
+			       rcu_state.name, j - gpa, j, gpa,
+			       READ_ONCE(jiffies_till_next_fqs),
+			       rcu_get_root()->qsmask);
+			/* In this case, the current CPU might be at fault. */
+			sched_show_task(current);
+		}
+	}
+	/* Rewrite if needed in case of slow consoles. */
+	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
+		WRITE_ONCE(rcu_state.jiffies_stall,
+			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
+
+	rcu_check_gp_kthread_starvation();
+
+	panic_on_rcu_stall();
+
+	rcu_force_quiescent_state();  /* Kick them all. */
+}
+
+static void print_cpu_stall(void)
+{
+	int cpu;
+	unsigned long flags;
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+	struct rcu_node *rnp = rcu_get_root();
+	long totqlen = 0;
+
+	/* Kick and suppress, if so configured. */
+	rcu_stall_kick_kthreads();
+	if (rcu_cpu_stall_suppress)
+		return;
+
+	/*
+	 * OK, time to rat on ourselves...
+	 * See Documentation/RCU/stallwarn.txt for info on how to debug
+	 * RCU CPU stall warnings.
+	 */
+	pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
+	raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
+	print_cpu_stall_info(smp_processor_id());
+	raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
+	for_each_possible_cpu(cpu)
+		totqlen += rcu_get_n_cbs_cpu(cpu);
+	pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
+		jiffies - rcu_state.gp_start,
+		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
+
+	rcu_check_gp_kthread_starvation();
+
+	rcu_dump_cpu_stacks();
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	/* Rewrite if needed in case of slow consoles. */
+	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
+		WRITE_ONCE(rcu_state.jiffies_stall,
+			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+	panic_on_rcu_stall();
+
+	/*
+	 * Attempt to revive the RCU machinery by forcing a context switch.
+	 *
+	 * A context switch would normally allow the RCU state machine to make
+	 * progress and it could be we're stuck in kernel space without context
+	 * switches for an entirely unreasonable amount of time.
+	 */
+	set_tsk_need_resched(current);
+	set_preempt_need_resched();
+}
+
+static void check_cpu_stall(struct rcu_data *rdp)
+{
+	unsigned long gs1;
+	unsigned long gs2;
+	unsigned long gps;
+	unsigned long j;
+	unsigned long jn;
+	unsigned long js;
+	struct rcu_node *rnp;
+
+	if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
+	    !rcu_gp_in_progress())
+		return;
+	rcu_stall_kick_kthreads();
+	j = jiffies;
+
+	/*
+	 * Lots of memory barriers to reject false positives.
+	 *
+	 * The idea is to pick up rcu_state.gp_seq, then
+	 * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
+	 * another copy of rcu_state.gp_seq.  These values are updated in
+	 * the opposite order with memory barriers (or equivalent) during
+	 * grace-period initialization and cleanup.  Now, a false positive
+	 * can occur if we get an new value of rcu_state.gp_start and a old
+	 * value of rcu_state.jiffies_stall.  But given the memory barriers,
+	 * the only way that this can happen is if one grace period ends
+	 * and another starts between these two fetches.  This is detected
+	 * by comparing the second fetch of rcu_state.gp_seq with the
+	 * previous fetch from rcu_state.gp_seq.
+	 *
+	 * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
+	 * and rcu_state.gp_start suffice to forestall false positives.
+	 */
+	gs1 = READ_ONCE(rcu_state.gp_seq);
+	smp_rmb(); /* Pick up ->gp_seq first... */
+	js = READ_ONCE(rcu_state.jiffies_stall);
+	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
+	gps = READ_ONCE(rcu_state.gp_start);
+	smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
+	gs2 = READ_ONCE(rcu_state.gp_seq);
+	if (gs1 != gs2 ||
+	    ULONG_CMP_LT(j, js) ||
+	    ULONG_CMP_GE(gps, js))
+		return; /* No stall or GP completed since entering function. */
+	rnp = rdp->mynode;
+	jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
+	if (rcu_gp_in_progress() &&
+	    (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
+	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
+
+		/* We haven't checked in, so go dump stack. */
+		print_cpu_stall();
+
+	} else if (rcu_gp_in_progress() &&
+		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
+		   cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
+
+		/* They had a few time units to dump stack, so complain. */
+		print_other_cpu_stall(gs2);
+	}
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// RCU forward-progress mechanisms, including of callback invocation.
+
+
+/*
+ * Show the state of the grace-period kthreads.
+ */
+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;
+	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 ? 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 %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) {
+			rdp = per_cpu_ptr(&rcu_data, cpu);
+			if (rdp->gpwrap ||
+			    ULONG_CMP_GE(rcu_state.gp_seq,
+					 rdp->gp_seq_needed))
+				continue;
+			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);
+
+/*
+ * This function checks for grace-period requests that fail to motivate
+ * RCU to come out of its idle mode.
+ */
+static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
+				     const unsigned long gpssdelay)
+{
+	unsigned long flags;
+	unsigned long j;
+	struct rcu_node *rnp_root = rcu_get_root();
+	static atomic_t warned = ATOMIC_INIT(0);
+
+	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
+	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
+		return;
+	j = jiffies; /* Expensive access, and in common case don't get here. */
+	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
+	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
+	    atomic_read(&warned))
+		return;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	j = jiffies;
+	if (rcu_gp_in_progress() ||
+	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
+	    time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
+	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
+	    atomic_read(&warned)) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	/* Hold onto the leaf lock to make others see warned==1. */
+
+	if (rnp_root != rnp)
+		raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
+	j = jiffies;
+	if (rcu_gp_in_progress() ||
+	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
+	    time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
+	    time_before(j, rcu_state.gp_activity + gpssdelay) ||
+	    atomic_xchg(&warned, 1)) {
+		raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	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();
+}
+
+/*
+ * Do a forward-progress check for rcutorture.  This is normally invoked
+ * due to an OOM event.  The argument "j" gives the time period during
+ * which rcutorture would like progress to have been made.
+ */
+void rcu_fwd_progress_check(unsigned long j)
+{
+	unsigned long cbs;
+	int cpu;
+	unsigned long max_cbs = 0;
+	int max_cpu = -1;
+	struct rcu_data *rdp;
+
+	if (rcu_gp_in_progress()) {
+		pr_info("%s: GP age %lu jiffies\n",
+			__func__, jiffies - rcu_state.gp_start);
+		show_rcu_gp_kthreads();
+	} else {
+		pr_info("%s: Last GP end %lu jiffies ago\n",
+			__func__, jiffies - rcu_state.gp_end);
+		preempt_disable();
+		rdp = this_cpu_ptr(&rcu_data);
+		rcu_check_gp_start_stall(rdp->mynode, rdp, j);
+		preempt_enable();
+	}
+	for_each_possible_cpu(cpu) {
+		cbs = rcu_get_n_cbs_cpu(cpu);
+		if (!cbs)
+			continue;
+		if (max_cpu < 0)
+			pr_info("%s: callbacks", __func__);
+		pr_cont(" %d: %lu", cpu, cbs);
+		if (cbs <= max_cbs)
+			continue;
+		max_cbs = cbs;
+		max_cpu = cpu;
+	}
+	if (max_cpu >= 0)
+		pr_cont("\n");
+}
+EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
+
+/* Commandeer a sysrq key to dump RCU's tree. */
+static bool sysrq_rcu;
+module_param(sysrq_rcu, bool, 0444);
+
+/* 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);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index cbaa976c5945..c3bf44ba42e5 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -424,68 +424,11 @@ EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 #endif
 
 #ifdef CONFIG_RCU_STALL_COMMON
-
-#ifdef CONFIG_PROVE_RCU
-#define RCU_STALL_DELAY_DELTA	       (5 * HZ)
-#else
-#define RCU_STALL_DELAY_DELTA	       0
-#endif
-
 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
 EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
-static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
-
 module_param(rcu_cpu_stall_suppress, int, 0644);
+int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 module_param(rcu_cpu_stall_timeout, int, 0644);
-
-int rcu_jiffies_till_stall_check(void)
-{
-	int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
-
-	/*
-	 * Limit check must be consistent with the Kconfig limits
-	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
-	 */
-	if (till_stall_check < 3) {
-		WRITE_ONCE(rcu_cpu_stall_timeout, 3);
-		till_stall_check = 3;
-	} else if (till_stall_check > 300) {
-		WRITE_ONCE(rcu_cpu_stall_timeout, 300);
-		till_stall_check = 300;
-	}
-	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
-}
-EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
-
-void rcu_sysrq_start(void)
-{
-	if (!rcu_cpu_stall_suppress)
-		rcu_cpu_stall_suppress = 2;
-}
-
-void rcu_sysrq_end(void)
-{
-	if (rcu_cpu_stall_suppress == 2)
-		rcu_cpu_stall_suppress = 0;
-}
-
-static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
-{
-	rcu_cpu_stall_suppress = 1;
-	return NOTIFY_DONE;
-}
-
-static struct notifier_block rcu_panic_block = {
-	.notifier_call = rcu_panic,
-};
-
-static int __init check_cpu_stall_init(void)
-{
-	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
-	return 0;
-}
-early_initcall(check_cpu_stall_init);
-
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 
 #ifdef CONFIG_TASKS_RCU
diff --git a/kernel/torture.c b/kernel/torture.c
index 8faa1a9aaeb9..17b2be9bde12 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -88,6 +88,8 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
 
 	if (!cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
 		return false;
+	if (num_online_cpus() <= 1)
+		return false;  /* Can't offline the last CPU. */
 
 	if (verbose > 1)
 		pr_alert("%s" TORTURE_FLAG