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 changes in this cycle were:

   - documentation updates

   - miscellaneous fixes

   - minor reorganization of code

   - torture-test updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits)
  rcu: Correctly handle sparse possible cpus
  rcu: sysctl: Panic on RCU Stall
  rcu: Fix a typo in a comment
  rcu: Make call_rcu_tasks() tolerate first call with irqs disabled
  rcu: Disable TASKS_RCU for usermode Linux
  rcu: No ordering for rcu_assign_pointer() of NULL
  rcutorture: Fix error return code in rcu_perf_init()
  torture: Inflict default jitter
  rcuperf: Don't treat gp_exp mis-setting as a WARN
  rcutorture: Drop "-soundhw pcspkr" from x86 boot arguments
  rcutorture: Don't specify the cpu type of QEMU on PPC
  rcutorture: Make -soundhw a x86 specific option
  rcutorture: Use vmlinux as the fallback kernel image
  rcutorture/doc: Create initrd using dracut
  torture: Stop onoff task if there is only one cpu
  torture: Add starvation events to error summary
  torture:  Break online and offline functions out of torture_onoff()
  torture: Forgive lengthy trace dumps and preemption
  torture: Remove CONFIG_RCU_TORTURE_TEST_RUNNABLE, simplify code
  torture: Simplify code, eliminate RCU_PERF_TEST_RUNNABLE
  ...

9 files changed, 844 insertions, 736 deletions

diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
index 3cee0d8393ed..d38ab08a3fe7 100644
--- a/kernel/rcu/rcuperf.c
+++ b/kernel/rcu/rcuperf.c
@@ -58,7 +58,7 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.vnet.ibm.com>");
 #define VERBOSE_PERFOUT_ERRSTRING(s) \
 	do { if (verbose) pr_alert("%s" PERF_FLAG "!!! %s\n", perf_type, s); } while (0)
 
-torture_param(bool, gp_exp, true, "Use expedited GP wait primitives");
+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");
@@ -96,12 +96,7 @@ static int rcu_perf_writer_state;
 #define MAX_MEAS 10000
 #define MIN_MEAS 100
 
-#if defined(MODULE) || defined(CONFIG_RCU_PERF_TEST_RUNNABLE)
-#define RCUPERF_RUNNABLE_INIT 1
-#else
-#define RCUPERF_RUNNABLE_INIT 0
-#endif
-static int perf_runnable = RCUPERF_RUNNABLE_INIT;
+static int perf_runnable = IS_ENABLED(MODULE);
 module_param(perf_runnable, int, 0444);
 MODULE_PARM_DESC(perf_runnable, "Start rcuperf at boot");
 
@@ -363,8 +358,6 @@ rcu_perf_writer(void *arg)
 	u64 *wdpp = writer_durations[me];
 
 	VERBOSE_PERFOUT_STRING("rcu_perf_writer task started");
-	WARN_ON(rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp);
-	WARN_ON(rcu_gp_is_normal() && gp_exp);
 	WARN_ON(!wdpp);
 	set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
 	sp.sched_priority = 1;
@@ -631,12 +624,24 @@ rcu_perf_init(void)
 		firsterr = -ENOMEM;
 		goto unwind;
 	}
+	if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp) {
+		VERBOSE_PERFOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!");
+		firsterr = -EINVAL;
+		goto unwind;
+	}
+	if (rcu_gp_is_normal() && gp_exp) {
+		VERBOSE_PERFOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!");
+		firsterr = -EINVAL;
+		goto unwind;
+	}
 	for (i = 0; i < nrealwriters; i++) {
 		writer_durations[i] =
 			kcalloc(MAX_MEAS, sizeof(*writer_durations[i]),
 				GFP_KERNEL);
-		if (!writer_durations[i])
+		if (!writer_durations[i]) {
+			firsterr = -ENOMEM;
 			goto unwind;
+		}
 		firsterr = torture_create_kthread(rcu_perf_writer, (void *)i,
 						  writer_tasks[i]);
 		if (firsterr)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 084a28a732eb..971e2b138063 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -182,12 +182,7 @@ static const char *rcu_torture_writer_state_getname(void)
 	return rcu_torture_writer_state_names[i];
 }
 
-#if defined(MODULE) || defined(CONFIG_RCU_TORTURE_TEST_RUNNABLE)
-#define RCUTORTURE_RUNNABLE_INIT 1
-#else
-#define RCUTORTURE_RUNNABLE_INIT 0
-#endif
-static int torture_runnable = RCUTORTURE_RUNNABLE_INIT;
+static int torture_runnable = IS_ENABLED(MODULE);
 module_param(torture_runnable, int, 0444);
 MODULE_PARM_DESC(torture_runnable, "Start rcutorture at boot");
 
@@ -1476,7 +1471,7 @@ static int rcu_torture_barrier_cbs(void *arg)
 			break;
 		/*
 		 * The above smp_load_acquire() ensures barrier_phase load
-		 * is ordered before the folloiwng ->call().
+		 * is ordered before the following ->call().
 		 */
 		local_irq_disable(); /* Just to test no-irq call_rcu(). */
 		cur_ops->call(&rcu, rcu_torture_barrier_cbf);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c7f1bc4f817c..f433959e9322 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -125,12 +125,14 @@ int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
 /* Number of rcu_nodes at specified level. */
 static 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;
 
 /*
  * The rcu_scheduler_active variable transitions from zero to one just
  * before the first task is spawned.  So when this variable is zero, RCU
  * can assume that there is but one task, allowing RCU to (for example)
- * optimize synchronize_sched() to a simple barrier().  When this variable
+ * optimize synchronize_rcu() to a simple barrier().  When this variable
  * is one, RCU must actually do all the hard work required to detect real
  * grace periods.  This variable is also used to suppress boot-time false
  * positives from lockdep-RCU error checking.
@@ -159,6 +161,7 @@ static void invoke_rcu_core(void);
 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
 static void rcu_report_exp_rdp(struct rcu_state *rsp,
 			       struct rcu_data *rdp, bool wake);
+static void sync_sched_exp_online_cleanup(int cpu);
 
 /* rcuc/rcub kthread realtime priority */
 #ifdef CONFIG_RCU_KTHREAD_PRIO
@@ -1284,9 +1287,9 @@ static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
 	rcu_for_each_leaf_node(rsp, rnp) {
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		if (rnp->qsmask != 0) {
-			for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
-				if (rnp->qsmask & (1UL << cpu))
-					dump_cpu_task(rnp->grplo + cpu);
+			for_each_leaf_node_possible_cpu(rnp, cpu)
+				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
+					dump_cpu_task(cpu);
 		}
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
@@ -1311,6 +1314,12 @@ static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
 	}
 }
 
+static inline void panic_on_rcu_stall(void)
+{
+	if (sysctl_panic_on_rcu_stall)
+		panic("RCU Stall\n");
+}
+
 static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 {
 	int cpu;
@@ -1351,10 +1360,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		ndetected += rcu_print_task_stall(rnp);
 		if (rnp->qsmask != 0) {
-			for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
-				if (rnp->qsmask & (1UL << cpu)) {
-					print_cpu_stall_info(rsp,
-							     rnp->grplo + cpu);
+			for_each_leaf_node_possible_cpu(rnp, cpu)
+				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+					print_cpu_stall_info(rsp, cpu);
 					ndetected++;
 				}
 		}
@@ -1390,6 +1398,8 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 
 	rcu_check_gp_kthread_starvation(rsp);
 
+	panic_on_rcu_stall();
+
 	force_quiescent_state(rsp);  /* Kick them all. */
 }
 
@@ -1430,6 +1440,8 @@ static void print_cpu_stall(struct rcu_state *rsp)
 			   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.
 	 *
@@ -1989,8 +2001,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
 	 * of the tree within the rsp->node[] array.  Note that other CPUs
 	 * will access only the leaves of the hierarchy, thus seeing that no
 	 * grace period is in progress, at least until the corresponding
-	 * leaf node has been initialized.  In addition, we have excluded
-	 * CPU-hotplug operations.
+	 * leaf node has been initialized.
 	 *
 	 * The grace period cannot complete until the initialization
 	 * process finishes, because this kthread handles both.
@@ -2872,7 +2883,6 @@ static void force_qs_rnp(struct rcu_state *rsp,
 				  unsigned long *maxj),
 			 bool *isidle, unsigned long *maxj)
 {
-	unsigned long bit;
 	int cpu;
 	unsigned long flags;
 	unsigned long mask;
@@ -2907,9 +2917,8 @@ static void force_qs_rnp(struct rcu_state *rsp,
 				continue;
 			}
 		}
-		cpu = rnp->grplo;
-		bit = 1;
-		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
+		for_each_leaf_node_possible_cpu(rnp, cpu) {
+			unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
 			if ((rnp->qsmask & bit) != 0) {
 				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
 					mask |= bit;
@@ -3448,549 +3457,6 @@ static bool rcu_seq_done(unsigned long *sp, unsigned long s)
 	return ULONG_CMP_GE(READ_ONCE(*sp), s);
 }
 
-/* Wrapper functions for expedited grace periods.  */
-static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
-{
-	rcu_seq_start(&rsp->expedited_sequence);
-}
-static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
-{
-	rcu_seq_end(&rsp->expedited_sequence);
-	smp_mb(); /* Ensure that consecutive grace periods serialize. */
-}
-static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
-{
-	unsigned long s;
-
-	smp_mb(); /* Caller's modifications seen first by other CPUs. */
-	s = rcu_seq_snap(&rsp->expedited_sequence);
-	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
-	return s;
-}
-static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
-{
-	return rcu_seq_done(&rsp->expedited_sequence, s);
-}
-
-/*
- * Reset the ->expmaskinit values in the rcu_node tree to reflect any
- * recent CPU-online activity.  Note that these masks are not cleared
- * when CPUs go offline, so they reflect the union of all CPUs that have
- * ever been online.  This means that this function normally takes its
- * no-work-to-do fastpath.
- */
-static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
-{
-	bool done;
-	unsigned long flags;
-	unsigned long mask;
-	unsigned long oldmask;
-	int ncpus = READ_ONCE(rsp->ncpus);
-	struct rcu_node *rnp;
-	struct rcu_node *rnp_up;
-
-	/* If no new CPUs onlined since last time, nothing to do. */
-	if (likely(ncpus == rsp->ncpus_snap))
-		return;
-	rsp->ncpus_snap = ncpus;
-
-	/*
-	 * Each pass through the following loop propagates newly onlined
-	 * CPUs for the current rcu_node structure up the rcu_node tree.
-	 */
-	rcu_for_each_leaf_node(rsp, rnp) {
-		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-		if (rnp->expmaskinit == rnp->expmaskinitnext) {
-			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-			continue;  /* No new CPUs, nothing to do. */
-		}
-
-		/* Update this node's mask, track old value for propagation. */
-		oldmask = rnp->expmaskinit;
-		rnp->expmaskinit = rnp->expmaskinitnext;
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
-		/* If was already nonzero, nothing to propagate. */
-		if (oldmask)
-			continue;
-
-		/* Propagate the new CPU up the tree. */
-		mask = rnp->grpmask;
-		rnp_up = rnp->parent;
-		done = false;
-		while (rnp_up) {
-			raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
-			if (rnp_up->expmaskinit)
-				done = true;
-			rnp_up->expmaskinit |= mask;
-			raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
-			if (done)
-				break;
-			mask = rnp_up->grpmask;
-			rnp_up = rnp_up->parent;
-		}
-	}
-}
-
-/*
- * Reset the ->expmask values in the rcu_node tree in preparation for
- * a new expedited grace period.
- */
-static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
-{
-	unsigned long flags;
-	struct rcu_node *rnp;
-
-	sync_exp_reset_tree_hotplug(rsp);
-	rcu_for_each_node_breadth_first(rsp, rnp) {
-		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-		WARN_ON_ONCE(rnp->expmask);
-		rnp->expmask = rnp->expmaskinit;
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-	}
-}
-
-/*
- * Return non-zero if there is no RCU expedited grace period in progress
- * for the specified rcu_node structure, in other words, if all CPUs and
- * tasks covered by the specified rcu_node structure have done their bit
- * for the current expedited grace period.  Works only for preemptible
- * RCU -- other RCU implementation use other means.
- *
- * Caller must hold the rcu_state's exp_mutex.
- */
-static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
-{
-	return rnp->exp_tasks == NULL &&
-	       READ_ONCE(rnp->expmask) == 0;
-}
-
-/*
- * Report the exit from RCU read-side critical section for the last task
- * that queued itself during or before the current expedited preemptible-RCU
- * grace period.  This event is reported either to the rcu_node structure on
- * which the task was queued or to one of that rcu_node structure's ancestors,
- * recursively up the tree.  (Calm down, calm down, we do the recursion
- * iteratively!)
- *
- * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
- * structure's ->lock.
- */
-static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
-				 bool wake, unsigned long flags)
-	__releases(rnp->lock)
-{
-	unsigned long mask;
-
-	for (;;) {
-		if (!sync_rcu_preempt_exp_done(rnp)) {
-			if (!rnp->expmask)
-				rcu_initiate_boost(rnp, flags);
-			else
-				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-			break;
-		}
-		if (rnp->parent == NULL) {
-			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-			if (wake) {
-				smp_mb(); /* EGP done before wake_up(). */
-				swake_up(&rsp->expedited_wq);
-			}
-			break;
-		}
-		mask = rnp->grpmask;
-		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
-		rnp = rnp->parent;
-		raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
-		WARN_ON_ONCE(!(rnp->expmask & mask));
-		rnp->expmask &= ~mask;
-	}
-}
-
-/*
- * Report expedited quiescent state for specified node.  This is a
- * lock-acquisition wrapper function for __rcu_report_exp_rnp().
- *
- * Caller must hold the rcu_state's exp_mutex.
- */
-static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
-					      struct rcu_node *rnp, bool wake)
-{
-	unsigned long flags;
-
-	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	__rcu_report_exp_rnp(rsp, rnp, wake, flags);
-}
-
-/*
- * Report expedited quiescent state for multiple CPUs, all covered by the
- * specified leaf rcu_node structure.  Caller must hold the rcu_state's
- * exp_mutex.
- */
-static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
-				    unsigned long mask, bool wake)
-{
-	unsigned long flags;
-
-	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	if (!(rnp->expmask & mask)) {
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-		return;
-	}
-	rnp->expmask &= ~mask;
-	__rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
-}
-
-/*
- * Report expedited quiescent state for specified rcu_data (CPU).
- */
-static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
-			       bool wake)
-{
-	rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
-}
-
-/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
-static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
-			       unsigned long s)
-{
-	if (rcu_exp_gp_seq_done(rsp, s)) {
-		trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
-		/* Ensure test happens before caller kfree(). */
-		smp_mb__before_atomic(); /* ^^^ */
-		atomic_long_inc(stat);
-		return true;
-	}
-	return false;
-}
-
-/*
- * Funnel-lock acquisition for expedited grace periods.  Returns true
- * if some other task completed an expedited grace period that this task
- * can piggy-back on, and with no mutex held.  Otherwise, returns false
- * with the mutex held, indicating that the caller must actually do the
- * expedited grace period.
- */
-static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
-{
-	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
-	struct rcu_node *rnp = rdp->mynode;
-	struct rcu_node *rnp_root = rcu_get_root(rsp);
-
-	/* Low-contention fastpath. */
-	if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
-	    (rnp == rnp_root ||
-	     ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
-	    !mutex_is_locked(&rsp->exp_mutex) &&
-	    mutex_trylock(&rsp->exp_mutex))
-		goto fastpath;
-
-	/*
-	 * Each pass through the following loop works its way up
-	 * the rcu_node tree, returning if others have done the work or
-	 * otherwise falls through to acquire rsp->exp_mutex.  The mapping
-	 * from CPU to rcu_node structure can be inexact, as it is just
-	 * promoting locality and is not strictly needed for correctness.
-	 */
-	for (; rnp != NULL; rnp = rnp->parent) {
-		if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
-			return true;
-
-		/* Work not done, either wait here or go up. */
-		spin_lock(&rnp->exp_lock);
-		if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
-
-			/* Someone else doing GP, so wait for them. */
-			spin_unlock(&rnp->exp_lock);
-			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
-						  rnp->grplo, rnp->grphi,
-						  TPS("wait"));
-			wait_event(rnp->exp_wq[(s >> 1) & 0x3],
-				   sync_exp_work_done(rsp,
-						      &rdp->exp_workdone2, s));
-			return true;
-		}
-		rnp->exp_seq_rq = s; /* Followers can wait on us. */
-		spin_unlock(&rnp->exp_lock);
-		trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,
-					  rnp->grphi, TPS("nxtlvl"));
-	}
-	mutex_lock(&rsp->exp_mutex);
-fastpath:
-	if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
-		mutex_unlock(&rsp->exp_mutex);
-		return true;
-	}
-	rcu_exp_gp_seq_start(rsp);
-	trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
-	return false;
-}
-
-/* Invoked on each online non-idle CPU for expedited quiescent state. */
-static void sync_sched_exp_handler(void *data)
-{
-	struct rcu_data *rdp;
-	struct rcu_node *rnp;
-	struct rcu_state *rsp = data;
-
-	rdp = this_cpu_ptr(rsp->rda);
-	rnp = rdp->mynode;
-	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
-	    __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
-		return;
-	if (rcu_is_cpu_rrupt_from_idle()) {
-		rcu_report_exp_rdp(&rcu_sched_state,
-				   this_cpu_ptr(&rcu_sched_data), true);
-		return;
-	}
-	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
-	resched_cpu(smp_processor_id());
-}
-
-/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
-static void sync_sched_exp_online_cleanup(int cpu)
-{
-	struct rcu_data *rdp;
-	int ret;
-	struct rcu_node *rnp;
-	struct rcu_state *rsp = &rcu_sched_state;
-
-	rdp = per_cpu_ptr(rsp->rda, cpu);
-	rnp = rdp->mynode;
-	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
-		return;
-	ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
-	WARN_ON_ONCE(ret);
-}
-
-/*
- * Select the nodes that the upcoming expedited grace period needs
- * to wait for.
- */
-static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
-				     smp_call_func_t func)
-{
-	int cpu;
-	unsigned long flags;
-	unsigned long mask;
-	unsigned long mask_ofl_test;
-	unsigned long mask_ofl_ipi;
-	int ret;
-	struct rcu_node *rnp;
-
-	sync_exp_reset_tree(rsp);
-	rcu_for_each_leaf_node(rsp, rnp) {
-		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-
-		/* Each pass checks a CPU for identity, offline, and idle. */
-		mask_ofl_test = 0;
-		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
-			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
-			struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
-
-			if (raw_smp_processor_id() == cpu ||
-			    !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
-				mask_ofl_test |= rdp->grpmask;
-		}
-		mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
-
-		/*
-		 * Need to wait for any blocked tasks as well.  Note that
-		 * additional blocking tasks will also block the expedited
-		 * GP until such time as the ->expmask bits are cleared.
-		 */
-		if (rcu_preempt_has_tasks(rnp))
-			rnp->exp_tasks = rnp->blkd_tasks.next;
-		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
-		/* IPI the remaining CPUs for expedited quiescent state. */
-		mask = 1;
-		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
-			if (!(mask_ofl_ipi & mask))
-				continue;
-retry_ipi:
-			ret = smp_call_function_single(cpu, func, rsp, 0);
-			if (!ret) {
-				mask_ofl_ipi &= ~mask;
-				continue;
-			}
-			/* Failed, raced with offline. */
-			raw_spin_lock_irqsave_rcu_node(rnp, flags);
-			if (cpu_online(cpu) &&
-			    (rnp->expmask & mask)) {
-				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-				schedule_timeout_uninterruptible(1);
-				if (cpu_online(cpu) &&
-				    (rnp->expmask & mask))
-					goto retry_ipi;
-				raw_spin_lock_irqsave_rcu_node(rnp, flags);
-			}
-			if (!(rnp->expmask & mask))
-				mask_ofl_ipi &= ~mask;
-			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-		}
-		/* Report quiescent states for those that went offline. */
-		mask_ofl_test |= mask_ofl_ipi;
-		if (mask_ofl_test)
-			rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
-	}
-}
-
-static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
-{
-	int cpu;
-	unsigned long jiffies_stall;
-	unsigned long jiffies_start;
-	unsigned long mask;
-	int ndetected;
-	struct rcu_node *rnp;
-	struct rcu_node *rnp_root = rcu_get_root(rsp);
-	int ret;
-
-	jiffies_stall = rcu_jiffies_till_stall_check();
-	jiffies_start = jiffies;
-
-	for (;;) {
-		ret = swait_event_timeout(
-				rsp->expedited_wq,
-				sync_rcu_preempt_exp_done(rnp_root),
-				jiffies_stall);
-		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
-			return;
-		if (ret < 0) {
-			/* Hit a signal, disable CPU stall warnings. */
-			swait_event(rsp->expedited_wq,
-				   sync_rcu_preempt_exp_done(rnp_root));
-			return;
-		}
-		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
-		       rsp->name);
-		ndetected = 0;
-		rcu_for_each_leaf_node(rsp, rnp) {
-			ndetected += rcu_print_task_exp_stall(rnp);
-			mask = 1;
-			for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
-				struct rcu_data *rdp;
-
-				if (!(rnp->expmask & mask))
-					continue;
-				ndetected++;
-				rdp = per_cpu_ptr(rsp->rda, cpu);
-				pr_cont(" %d-%c%c%c", cpu,
-					"O."[!!cpu_online(cpu)],
-					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
-					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
-			}
-			mask <<= 1;
-		}
-		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
-			jiffies - jiffies_start, rsp->expedited_sequence,
-			rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
-		if (ndetected) {
-			pr_err("blocking rcu_node structures:");
-			rcu_for_each_node_breadth_first(rsp, rnp) {
-				if (rnp == rnp_root)
-					continue; /* printed unconditionally */
-				if (sync_rcu_preempt_exp_done(rnp))
-					continue;
-				pr_cont(" l=%u:%d-%d:%#lx/%c",
-					rnp->level, rnp->grplo, rnp->grphi,
-					rnp->expmask,
-					".T"[!!rnp->exp_tasks]);
-			}
-			pr_cont("\n");
-		}
-		rcu_for_each_leaf_node(rsp, rnp) {
-			mask = 1;
-			for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
-				if (!(rnp->expmask & mask))
-					continue;
-				dump_cpu_task(cpu);
-			}
-		}
-		jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
-	}
-}
-
-/*
- * Wait for the current expedited grace period to complete, and then
- * wake up everyone who piggybacked on the just-completed expedited
- * grace period.  Also update all the ->exp_seq_rq counters as needed
- * in order to avoid counter-wrap problems.
- */
-static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
-{
-	struct rcu_node *rnp;
-
-	synchronize_sched_expedited_wait(rsp);
-	rcu_exp_gp_seq_end(rsp);
-	trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
-
-	/*
-	 * Switch over to wakeup mode, allowing the next GP, but -only- the
-	 * next GP, to proceed.
-	 */
-	mutex_lock(&rsp->exp_wake_mutex);
-	mutex_unlock(&rsp->exp_mutex);
-
-	rcu_for_each_node_breadth_first(rsp, rnp) {
-		if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
-			spin_lock(&rnp->exp_lock);
-			/* Recheck, avoid hang in case someone just arrived. */
-			if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
-				rnp->exp_seq_rq = s;
-			spin_unlock(&rnp->exp_lock);
-		}
-		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
-	}
-	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
-	mutex_unlock(&rsp->exp_wake_mutex);
-}
-
-/**
- * synchronize_sched_expedited - Brute-force RCU-sched grace period
- *
- * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
- * approach to force the grace period to end quickly.  This consumes
- * significant time on all CPUs and is unfriendly to real-time workloads,
- * so is thus not recommended for any sort of common-case code.  In fact,
- * if you are using synchronize_sched_expedited() in a loop, please
- * restructure your code to batch your updates, and then use a single
- * synchronize_sched() instead.
- *
- * This implementation can be thought of as an application of sequence
- * locking to expedited grace periods, but using the sequence counter to
- * determine when someone else has already done the work instead of for
- * retrying readers.
- */
-void synchronize_sched_expedited(void)
-{
-	unsigned long s;
-	struct rcu_state *rsp = &rcu_sched_state;
-
-	/* If only one CPU, this is automatically a grace period. */
-	if (rcu_blocking_is_gp())
-		return;
-
-	/* If expedited grace periods are prohibited, fall back to normal. */
-	if (rcu_gp_is_normal()) {
-		wait_rcu_gp(call_rcu_sched);
-		return;
-	}
-
-	/* Take a snapshot of the sequence number.  */
-	s = rcu_exp_gp_seq_snap(rsp);
-	if (exp_funnel_lock(rsp, s))
-		return;  /* Someone else did our work for us. */
-
-	/* Initialize the rcu_node tree in preparation for the wait. */
-	sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
-
-	/* Wait and clean up, including waking everyone. */
-	rcu_exp_wait_wake(rsp, s);
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
 /*
  * Check to see if there is any immediate RCU-related work to be done
  * by the current CPU, for the specified type of RCU, returning 1 if so.
@@ -4281,7 +3747,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
 
 	/* Set up local state, ensuring consistent view of global state. */
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
+	rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
 	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
 	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
 	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
@@ -4364,9 +3830,6 @@ static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
 	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
-	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
-		return;
-
 	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
 	mask = rdp->grpmask;
 	raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
@@ -4751,4 +4214,5 @@ void __init rcu_init(void)
 		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
 }
 
+#include "tree_exp.h"
 #include "tree_plugin.h"
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index e3959f5e6ddf..f714f873bf9d 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -254,6 +254,13 @@ struct rcu_node {
 } ____cacheline_internodealigned_in_smp;
 
 /*
+ * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
+ * are indexed relative to this interval rather than the global CPU ID space.
+ * This generates the bit for a CPU in node-local masks.
+ */
+#define leaf_node_cpu_bit(rnp, cpu) (1UL << ((cpu) - (rnp)->grplo))
+
+/*
  * Do a full breadth-first scan of the rcu_node structures for the
  * specified rcu_state structure.
  */
@@ -281,6 +288,14 @@ struct rcu_node {
 	     (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
 
 /*
+ * Iterate over all possible CPUs in a leaf RCU node.
+ */
+#define for_each_leaf_node_possible_cpu(rnp, cpu) \
+	for ((cpu) = cpumask_next(rnp->grplo - 1, cpu_possible_mask); \
+	     cpu <= rnp->grphi; \
+	     cpu = cpumask_next((cpu), cpu_possible_mask))
+
+/*
  * Union to allow "aggregate OR" operation on the need for a quiescent
  * state by the normal and expedited grace periods.
  */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
new file mode 100644
index 000000000000..d400434af6b2
--- /dev/null
+++ b/kernel/rcu/tree_exp.h
@@ -0,0 +1,656 @@
+/*
+ * 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>
+ */
+
+/* Wrapper functions for expedited grace periods.  */
+static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
+{
+	rcu_seq_start(&rsp->expedited_sequence);
+}
+static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
+{
+	rcu_seq_end(&rsp->expedited_sequence);
+	smp_mb(); /* Ensure that consecutive grace periods serialize. */
+}
+static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
+{
+	unsigned long s;
+
+	smp_mb(); /* Caller's modifications seen first by other CPUs. */
+	s = rcu_seq_snap(&rsp->expedited_sequence);
+	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
+	return s;
+}
+static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
+{
+	return rcu_seq_done(&rsp->expedited_sequence, s);
+}
+
+/*
+ * Reset the ->expmaskinit values in the rcu_node tree to reflect any
+ * recent CPU-online activity.  Note that these masks are not cleared
+ * when CPUs go offline, so they reflect the union of all CPUs that have
+ * ever been online.  This means that this function normally takes its
+ * no-work-to-do fastpath.
+ */
+static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
+{
+	bool done;
+	unsigned long flags;
+	unsigned long mask;
+	unsigned long oldmask;
+	int ncpus = READ_ONCE(rsp->ncpus);
+	struct rcu_node *rnp;
+	struct rcu_node *rnp_up;
+
+	/* If no new CPUs onlined since last time, nothing to do. */
+	if (likely(ncpus == rsp->ncpus_snap))
+		return;
+	rsp->ncpus_snap = ncpus;
+
+	/*
+	 * Each pass through the following loop propagates newly onlined
+	 * CPUs for the current rcu_node structure up the rcu_node tree.
+	 */
+	rcu_for_each_leaf_node(rsp, rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		if (rnp->expmaskinit == rnp->expmaskinitnext) {
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			continue;  /* No new CPUs, nothing to do. */
+		}
+
+		/* Update this node's mask, track old value for propagation. */
+		oldmask = rnp->expmaskinit;
+		rnp->expmaskinit = rnp->expmaskinitnext;
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+		/* If was already nonzero, nothing to propagate. */
+		if (oldmask)
+			continue;
+
+		/* Propagate the new CPU up the tree. */
+		mask = rnp->grpmask;
+		rnp_up = rnp->parent;
+		done = false;
+		while (rnp_up) {
+			raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
+			if (rnp_up->expmaskinit)
+				done = true;
+			rnp_up->expmaskinit |= mask;
+			raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
+			if (done)
+				break;
+			mask = rnp_up->grpmask;
+			rnp_up = rnp_up->parent;
+		}
+	}
+}
+
+/*
+ * Reset the ->expmask values in the rcu_node tree in preparation for
+ * a new expedited grace period.
+ */
+static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
+{
+	unsigned long flags;
+	struct rcu_node *rnp;
+
+	sync_exp_reset_tree_hotplug(rsp);
+	rcu_for_each_node_breadth_first(rsp, rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		WARN_ON_ONCE(rnp->expmask);
+		rnp->expmask = rnp->expmaskinit;
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+}
+
+/*
+ * Return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period.  Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold the rcu_state's exp_mutex.
+ */
+static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+{
+	return rnp->exp_tasks == NULL &&
+	       READ_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period.  This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree.  (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
+ * structure's ->lock.
+ */
+static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+				 bool wake, unsigned long flags)
+	__releases(rnp->lock)
+{
+	unsigned long mask;
+
+	for (;;) {
+		if (!sync_rcu_preempt_exp_done(rnp)) {
+			if (!rnp->expmask)
+				rcu_initiate_boost(rnp, flags);
+			else
+				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			break;
+		}
+		if (rnp->parent == NULL) {
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			if (wake) {
+				smp_mb(); /* EGP done before wake_up(). */
+				swake_up(&rsp->expedited_wq);
+			}
+			break;
+		}
+		mask = rnp->grpmask;
+		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
+		rnp = rnp->parent;
+		raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
+		WARN_ON_ONCE(!(rnp->expmask & mask));
+		rnp->expmask &= ~mask;
+	}
+}
+
+/*
+ * Report expedited quiescent state for specified node.  This is a
+ * lock-acquisition wrapper function for __rcu_report_exp_rnp().
+ *
+ * Caller must hold the rcu_state's exp_mutex.
+ */
+static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
+					      struct rcu_node *rnp, bool wake)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	__rcu_report_exp_rnp(rsp, rnp, wake, flags);
+}
+
+/*
+ * Report expedited quiescent state for multiple CPUs, all covered by the
+ * specified leaf rcu_node structure.  Caller must hold the rcu_state's
+ * exp_mutex.
+ */
+static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
+				    unsigned long mask, bool wake)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	if (!(rnp->expmask & mask)) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	rnp->expmask &= ~mask;
+	__rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
+}
+
+/*
+ * Report expedited quiescent state for specified rcu_data (CPU).
+ */
+static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
+			       bool wake)
+{
+	rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
+}
+
+/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
+static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
+			       unsigned long s)
+{
+	if (rcu_exp_gp_seq_done(rsp, s)) {
+		trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
+		/* Ensure test happens before caller kfree(). */
+		smp_mb__before_atomic(); /* ^^^ */
+		atomic_long_inc(stat);
+		return true;
+	}
+	return false;
+}
+
+/*
+ * Funnel-lock acquisition for expedited grace periods.  Returns true
+ * if some other task completed an expedited grace period that this task
+ * can piggy-back on, and with no mutex held.  Otherwise, returns false
+ * with the mutex held, indicating that the caller must actually do the
+ * expedited grace period.
+ */
+static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
+{
+	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
+	struct rcu_node *rnp = rdp->mynode;
+	struct rcu_node *rnp_root = rcu_get_root(rsp);
+
+	/* Low-contention fastpath. */
+	if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
+	    (rnp == rnp_root ||
+	     ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
+	    !mutex_is_locked(&rsp->exp_mutex) &&
+	    mutex_trylock(&rsp->exp_mutex))
+		goto fastpath;
+
+	/*
+	 * Each pass through the following loop works its way up
+	 * the rcu_node tree, returning if others have done the work or
+	 * otherwise falls through to acquire rsp->exp_mutex.  The mapping
+	 * from CPU to rcu_node structure can be inexact, as it is just
+	 * promoting locality and is not strictly needed for correctness.
+	 */
+	for (; rnp != NULL; rnp = rnp->parent) {
+		if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
+			return true;
+
+		/* Work not done, either wait here or go up. */
+		spin_lock(&rnp->exp_lock);
+		if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
+
+			/* Someone else doing GP, so wait for them. */
+			spin_unlock(&rnp->exp_lock);
+			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
+						  rnp->grplo, rnp->grphi,
+						  TPS("wait"));
+			wait_event(rnp->exp_wq[(s >> 1) & 0x3],
+				   sync_exp_work_done(rsp,
+						      &rdp->exp_workdone2, s));
+			return true;
+		}
+		rnp->exp_seq_rq = s; /* Followers can wait on us. */
+		spin_unlock(&rnp->exp_lock);
+		trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,
+					  rnp->grphi, TPS("nxtlvl"));
+	}
+	mutex_lock(&rsp->exp_mutex);
+fastpath:
+	if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
+		mutex_unlock(&rsp->exp_mutex);
+		return true;
+	}
+	rcu_exp_gp_seq_start(rsp);
+	trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
+	return false;
+}
+
+/* Invoked on each online non-idle CPU for expedited quiescent state. */
+static void sync_sched_exp_handler(void *data)
+{
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	struct rcu_state *rsp = data;
+
+	rdp = this_cpu_ptr(rsp->rda);
+	rnp = rdp->mynode;
+	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
+	    __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
+		return;
+	if (rcu_is_cpu_rrupt_from_idle()) {
+		rcu_report_exp_rdp(&rcu_sched_state,
+				   this_cpu_ptr(&rcu_sched_data), true);
+		return;
+	}
+	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
+	resched_cpu(smp_processor_id());
+}
+
+/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
+static void sync_sched_exp_online_cleanup(int cpu)
+{
+	struct rcu_data *rdp;
+	int ret;
+	struct rcu_node *rnp;
+	struct rcu_state *rsp = &rcu_sched_state;
+
+	rdp = per_cpu_ptr(rsp->rda, cpu);
+	rnp = rdp->mynode;
+	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
+		return;
+	ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
+	WARN_ON_ONCE(ret);
+}
+
+/*
+ * Select the nodes that the upcoming expedited grace period needs
+ * to wait for.
+ */
+static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
+				     smp_call_func_t func)
+{
+	int cpu;
+	unsigned long flags;
+	unsigned long mask_ofl_test;
+	unsigned long mask_ofl_ipi;
+	int ret;
+	struct rcu_node *rnp;
+
+	sync_exp_reset_tree(rsp);
+	rcu_for_each_leaf_node(rsp, rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+
+		/* Each pass checks a CPU for identity, offline, and idle. */
+		mask_ofl_test = 0;
+		for_each_leaf_node_possible_cpu(rnp, cpu) {
+			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+			struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+
+			if (raw_smp_processor_id() == cpu ||
+			    !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
+				mask_ofl_test |= rdp->grpmask;
+		}
+		mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
+
+		/*
+		 * Need to wait for any blocked tasks as well.  Note that
+		 * additional blocking tasks will also block the expedited
+		 * GP until such time as the ->expmask bits are cleared.
+		 */
+		if (rcu_preempt_has_tasks(rnp))
+			rnp->exp_tasks = rnp->blkd_tasks.next;
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+		/* IPI the remaining CPUs for expedited quiescent state. */
+		for_each_leaf_node_possible_cpu(rnp, cpu) {
+			unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
+			if (!(mask_ofl_ipi & mask))
+				continue;
+retry_ipi:
+			ret = smp_call_function_single(cpu, func, rsp, 0);
+			if (!ret) {
+				mask_ofl_ipi &= ~mask;
+				continue;
+			}
+			/* Failed, raced with offline. */
+			raw_spin_lock_irqsave_rcu_node(rnp, flags);
+			if (cpu_online(cpu) &&
+			    (rnp->expmask & mask)) {
+				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+				schedule_timeout_uninterruptible(1);
+				if (cpu_online(cpu) &&
+				    (rnp->expmask & mask))
+					goto retry_ipi;
+				raw_spin_lock_irqsave_rcu_node(rnp, flags);
+			}
+			if (!(rnp->expmask & mask))
+				mask_ofl_ipi &= ~mask;
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		}
+		/* Report quiescent states for those that went offline. */
+		mask_ofl_test |= mask_ofl_ipi;
+		if (mask_ofl_test)
+			rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
+	}
+}
+
+static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
+{
+	int cpu;
+	unsigned long jiffies_stall;
+	unsigned long jiffies_start;
+	unsigned long mask;
+	int ndetected;
+	struct rcu_node *rnp;
+	struct rcu_node *rnp_root = rcu_get_root(rsp);
+	int ret;
+
+	jiffies_stall = rcu_jiffies_till_stall_check();
+	jiffies_start = jiffies;
+
+	for (;;) {
+		ret = swait_event_timeout(
+				rsp->expedited_wq,
+				sync_rcu_preempt_exp_done(rnp_root),
+				jiffies_stall);
+		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
+			return;
+		if (ret < 0) {
+			/* Hit a signal, disable CPU stall warnings. */
+			swait_event(rsp->expedited_wq,
+				   sync_rcu_preempt_exp_done(rnp_root));
+			return;
+		}
+		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
+		       rsp->name);
+		ndetected = 0;
+		rcu_for_each_leaf_node(rsp, rnp) {
+			ndetected += rcu_print_task_exp_stall(rnp);
+			for_each_leaf_node_possible_cpu(rnp, cpu) {
+				struct rcu_data *rdp;
+
+				mask = leaf_node_cpu_bit(rnp, cpu);
+				if (!(rnp->expmask & mask))
+					continue;
+				ndetected++;
+				rdp = per_cpu_ptr(rsp->rda, cpu);
+				pr_cont(" %d-%c%c%c", cpu,
+					"O."[!!cpu_online(cpu)],
+					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
+					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
+			}
+		}
+		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
+			jiffies - jiffies_start, rsp->expedited_sequence,
+			rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
+		if (ndetected) {
+			pr_err("blocking rcu_node structures:");
+			rcu_for_each_node_breadth_first(rsp, rnp) {
+				if (rnp == rnp_root)
+					continue; /* printed unconditionally */
+				if (sync_rcu_preempt_exp_done(rnp))
+					continue;
+				pr_cont(" l=%u:%d-%d:%#lx/%c",
+					rnp->level, rnp->grplo, rnp->grphi,
+					rnp->expmask,
+					".T"[!!rnp->exp_tasks]);
+			}
+			pr_cont("\n");
+		}
+		rcu_for_each_leaf_node(rsp, rnp) {
+			for_each_leaf_node_possible_cpu(rnp, cpu) {
+				mask = leaf_node_cpu_bit(rnp, cpu);
+				if (!(rnp->expmask & mask))
+					continue;
+				dump_cpu_task(cpu);
+			}
+		}
+		jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
+	}
+}
+
+/*
+ * Wait for the current expedited grace period to complete, and then
+ * wake up everyone who piggybacked on the just-completed expedited
+ * grace period.  Also update all the ->exp_seq_rq counters as needed
+ * in order to avoid counter-wrap problems.
+ */
+static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
+{
+	struct rcu_node *rnp;
+
+	synchronize_sched_expedited_wait(rsp);
+	rcu_exp_gp_seq_end(rsp);
+	trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
+
+	/*
+	 * Switch over to wakeup mode, allowing the next GP, but -only- the
+	 * next GP, to proceed.
+	 */
+	mutex_lock(&rsp->exp_wake_mutex);
+	mutex_unlock(&rsp->exp_mutex);
+
+	rcu_for_each_node_breadth_first(rsp, rnp) {
+		if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
+			spin_lock(&rnp->exp_lock);
+			/* Recheck, avoid hang in case someone just arrived. */
+			if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
+				rnp->exp_seq_rq = s;
+			spin_unlock(&rnp->exp_lock);
+		}
+		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);
+	}
+	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
+	mutex_unlock(&rsp->exp_wake_mutex);
+}
+
+/**
+ * synchronize_sched_expedited - Brute-force RCU-sched grace period
+ *
+ * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
+ * approach to force the grace period to end quickly.  This consumes
+ * significant time on all CPUs and is unfriendly to real-time workloads,
+ * so is thus not recommended for any sort of common-case code.  In fact,
+ * if you are using synchronize_sched_expedited() in a loop, please
+ * restructure your code to batch your updates, and then use a single
+ * synchronize_sched() instead.
+ *
+ * This implementation can be thought of as an application of sequence
+ * locking to expedited grace periods, but using the sequence counter to
+ * determine when someone else has already done the work instead of for
+ * retrying readers.
+ */
+void synchronize_sched_expedited(void)
+{
+	unsigned long s;
+	struct rcu_state *rsp = &rcu_sched_state;
+
+	/* If only one CPU, this is automatically a grace period. */
+	if (rcu_blocking_is_gp())
+		return;
+
+	/* If expedited grace periods are prohibited, fall back to normal. */
+	if (rcu_gp_is_normal()) {
+		wait_rcu_gp(call_rcu_sched);
+		return;
+	}
+
+	/* Take a snapshot of the sequence number.  */
+	s = rcu_exp_gp_seq_snap(rsp);
+	if (exp_funnel_lock(rsp, s))
+		return;  /* Someone else did our work for us. */
+
+	/* Initialize the rcu_node tree in preparation for the wait. */
+	sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
+
+	/* Wait and clean up, including waking everyone. */
+	rcu_exp_wait_wake(rsp, s);
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#ifdef CONFIG_PREEMPT_RCU
+
+/*
+ * Remote handler for smp_call_function_single().  If there is an
+ * RCU read-side critical section in effect, request that the
+ * next rcu_read_unlock() record the quiescent state up the
+ * ->expmask fields in the rcu_node tree.  Otherwise, immediately
+ * report the quiescent state.
+ */
+static void sync_rcu_exp_handler(void *info)
+{
+	struct rcu_data *rdp;
+	struct rcu_state *rsp = info;
+	struct task_struct *t = current;
+
+	/*
+	 * Within an RCU read-side critical section, request that the next
+	 * rcu_read_unlock() report.  Unless this RCU read-side critical
+	 * section has already blocked, in which case it is already set
+	 * up for the expedited grace period to wait on it.
+	 */
+	if (t->rcu_read_lock_nesting > 0 &&
+	    !t->rcu_read_unlock_special.b.blocked) {
+		t->rcu_read_unlock_special.b.exp_need_qs = true;
+		return;
+	}
+
+	/*
+	 * We are either exiting an RCU read-side critical section (negative
+	 * values of t->rcu_read_lock_nesting) or are not in one at all
+	 * (zero value of t->rcu_read_lock_nesting).  Or we are in an RCU
+	 * read-side critical section that blocked before this expedited
+	 * grace period started.  Either way, we can immediately report
+	 * the quiescent state.
+	 */
+	rdp = this_cpu_ptr(rsp->rda);
+	rcu_report_exp_rdp(rsp, rdp, true);
+}
+
+/**
+ * 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.
+ */
+void synchronize_rcu_expedited(void)
+{
+	struct rcu_state *rsp = rcu_state_p;
+	unsigned long s;
+
+	/* If expedited grace periods are prohibited, fall back to normal. */
+	if (rcu_gp_is_normal()) {
+		wait_rcu_gp(call_rcu);
+		return;
+	}
+
+	s = rcu_exp_gp_seq_snap(rsp);
+	if (exp_funnel_lock(rsp, s))
+		return;  /* Someone else did our work for us. */
+
+	/* Initialize the rcu_node tree in preparation for the wait. */
+	sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler);
+
+	/* Wait for ->blkd_tasks lists to drain, then wake everyone up. */
+	rcu_exp_wait_wake(rsp, s);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/*
+ * Wait for an rcu-preempt grace period, but make it happen quickly.
+ * But because preemptible RCU does not exist, map to rcu-sched.
+ */
+void synchronize_rcu_expedited(void)
+{
+	synchronize_sched_expedited();
+}
+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 ff1cd4e1188d..0082fce402a0 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -79,8 +79,6 @@ static void __init rcu_bootup_announce_oddness(void)
 		pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
 	if (IS_ENABLED(CONFIG_PROVE_RCU))
 		pr_info("\tRCU lockdep checking is enabled.\n");
-	if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE))
-		pr_info("\tRCU torture testing starts during boot.\n");
 	if (RCU_NUM_LVLS >= 4)
 		pr_info("\tFour(or more)-level hierarchy is enabled.\n");
 	if (RCU_FANOUT_LEAF != 16)
@@ -681,84 +679,6 @@ void synchronize_rcu(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu);
 
-/*
- * Remote handler for smp_call_function_single().  If there is an
- * RCU read-side critical section in effect, request that the
- * next rcu_read_unlock() record the quiescent state up the
- * ->expmask fields in the rcu_node tree.  Otherwise, immediately
- * report the quiescent state.
- */
-static void sync_rcu_exp_handler(void *info)
-{
-	struct rcu_data *rdp;
-	struct rcu_state *rsp = info;
-	struct task_struct *t = current;
-
-	/*
-	 * Within an RCU read-side critical section, request that the next
-	 * rcu_read_unlock() report.  Unless this RCU read-side critical
-	 * section has already blocked, in which case it is already set
-	 * up for the expedited grace period to wait on it.
-	 */
-	if (t->rcu_read_lock_nesting > 0 &&
-	    !t->rcu_read_unlock_special.b.blocked) {
-		t->rcu_read_unlock_special.b.exp_need_qs = true;
-		return;
-	}
-
-	/*
-	 * We are either exiting an RCU read-side critical section (negative
-	 * values of t->rcu_read_lock_nesting) or are not in one at all
-	 * (zero value of t->rcu_read_lock_nesting).  Or we are in an RCU
-	 * read-side critical section that blocked before this expedited
-	 * grace period started.  Either way, we can immediately report
-	 * the quiescent state.
-	 */
-	rdp = this_cpu_ptr(rsp->rda);
-	rcu_report_exp_rdp(rsp, rdp, true);
-}
-
-/**
- * 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.
- */
-void synchronize_rcu_expedited(void)
-{
-	struct rcu_state *rsp = rcu_state_p;
-	unsigned long s;
-
-	/* If expedited grace periods are prohibited, fall back to normal. */
-	if (rcu_gp_is_normal()) {
-		wait_rcu_gp(call_rcu);
-		return;
-	}
-
-	s = rcu_exp_gp_seq_snap(rsp);
-	if (exp_funnel_lock(rsp, s))
-		return;  /* Someone else did our work for us. */
-
-	/* Initialize the rcu_node tree in preparation for the wait. */
-	sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler);
-
-	/* Wait for ->blkd_tasks lists to drain, then wake everyone up. */
-	rcu_exp_wait_wake(rsp, s);
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
 /**
  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
  *
@@ -883,16 +803,6 @@ static void rcu_preempt_check_callbacks(void)
 }
 
 /*
- * Wait for an rcu-preempt grace period, but make it happen quickly.
- * But because preemptible RCU does not exist, map to rcu-sched.
- */
-void synchronize_rcu_expedited(void)
-{
-	synchronize_sched_expedited();
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
-/*
  * Because preemptible RCU does not exist, rcu_barrier() is just
  * another name for rcu_barrier_sched().
  */
@@ -1254,8 +1164,9 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 		return;
 	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
 		return;
-	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
-		if ((mask & 0x1) && cpu != outgoingcpu)
+	for_each_leaf_node_possible_cpu(rnp, cpu)
+		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
+		    cpu != outgoingcpu)
 			cpumask_set_cpu(cpu, cm);
 	if (cpumask_weight(cm) == 0)
 		cpumask_setall(cm);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 3e888cd5a594..f0d8322bc3ec 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -528,6 +528,7 @@ static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
 module_param(rcu_task_stall_timeout, int, 0644);
 
 static void rcu_spawn_tasks_kthread(void);
+static struct task_struct *rcu_tasks_kthread_ptr;
 
 /*
  * Post an RCU-tasks callback.  First call must be from process context
@@ -537,6 +538,7 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
 {
 	unsigned long flags;
 	bool needwake;
+	bool havetask = READ_ONCE(rcu_tasks_kthread_ptr);
 
 	rhp->next = NULL;
 	rhp->func = func;
@@ -545,7 +547,9 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
 	*rcu_tasks_cbs_tail = rhp;
 	rcu_tasks_cbs_tail = &rhp->next;
 	raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
-	if (needwake) {
+	/* We can't create the thread unless interrupts are enabled. */
+	if ((needwake && havetask) ||
+	    (!havetask && !irqs_disabled_flags(flags))) {
 		rcu_spawn_tasks_kthread();
 		wake_up(&rcu_tasks_cbs_wq);
 	}
@@ -790,7 +794,6 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 static void rcu_spawn_tasks_kthread(void)
 {
 	static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
-	static struct task_struct *rcu_tasks_kthread_ptr;
 	struct task_struct *t;
 
 	if (READ_ONCE(rcu_tasks_kthread_ptr)) {
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 87b2fc38398b..35f0dcb1cb4f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1205,6 +1205,17 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &one,
 	},
 #endif
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+	{
+		.procname	= "panic_on_rcu_stall",
+		.data		= &sysctl_panic_on_rcu_stall,
+		.maxlen		= sizeof(sysctl_panic_on_rcu_stall),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
+#endif
 	{ }
 };
 
diff --git a/kernel/torture.c b/kernel/torture.c
index fa0bdeee17ac..75961b3decfe 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -82,6 +82,104 @@ static int min_online = -1;
 static int max_online;
 
 /*
+ * Attempt to take a CPU offline.  Return false if the CPU is already
+ * offline or if it is not subject to CPU-hotplug operations.  The
+ * caller can detect other failures by looking at the statistics.
+ */
+bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
+		     unsigned long *sum_offl, int *min_offl, int *max_offl)
+{
+	unsigned long delta;
+	int ret;
+	unsigned long starttime;
+
+	if (!cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
+		return false;
+
+	if (verbose)
+		pr_alert("%s" TORTURE_FLAG
+			 "torture_onoff task: offlining %d\n",
+			 torture_type, cpu);
+	starttime = jiffies;
+	(*n_offl_attempts)++;
+	ret = cpu_down(cpu);
+	if (ret) {
+		if (verbose)
+			pr_alert("%s" TORTURE_FLAG
+				 "torture_onoff task: offline %d failed: errno %d\n",
+				 torture_type, cpu, ret);
+	} else {
+		if (verbose)
+			pr_alert("%s" TORTURE_FLAG
+				 "torture_onoff task: offlined %d\n",
+				 torture_type, cpu);
+		(*n_offl_successes)++;
+		delta = jiffies - starttime;
+		sum_offl += delta;
+		if (*min_offl < 0) {
+			*min_offl = delta;
+			*max_offl = delta;
+		}
+		if (*min_offl > delta)
+			*min_offl = delta;
+		if (*max_offl < delta)
+			*max_offl = delta;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(torture_offline);
+
+/*
+ * Attempt to bring a CPU online.  Return false if the CPU is already
+ * online or if it is not subject to CPU-hotplug operations.  The
+ * caller can detect other failures by looking at the statistics.
+ */
+bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes,
+		    unsigned long *sum_onl, int *min_onl, int *max_onl)
+{
+	unsigned long delta;
+	int ret;
+	unsigned long starttime;
+
+	if (cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
+		return false;
+
+	if (verbose)
+		pr_alert("%s" TORTURE_FLAG
+			 "torture_onoff task: onlining %d\n",
+			 torture_type, cpu);
+	starttime = jiffies;
+	(*n_onl_attempts)++;
+	ret = cpu_up(cpu);
+	if (ret) {
+		if (verbose)
+			pr_alert("%s" TORTURE_FLAG
+				 "torture_onoff task: online %d failed: errno %d\n",
+				 torture_type, cpu, ret);
+	} else {
+		if (verbose)
+			pr_alert("%s" TORTURE_FLAG
+				 "torture_onoff task: onlined %d\n",
+				 torture_type, cpu);
+		(*n_onl_successes)++;
+		delta = jiffies - starttime;
+		*sum_onl += delta;
+		if (*min_onl < 0) {
+			*min_onl = delta;
+			*max_onl = delta;
+		}
+		if (*min_onl > delta)
+			*min_onl = delta;
+		if (*max_onl < delta)
+			*max_onl = delta;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(torture_online);
+
+/*
  * Execute random CPU-hotplug operations at the interval specified
  * by the onoff_interval.
  */
@@ -89,16 +187,19 @@ static int
 torture_onoff(void *arg)
 {
 	int cpu;
-	unsigned long delta;
 	int maxcpu = -1;
 	DEFINE_TORTURE_RANDOM(rand);
-	int ret;
-	unsigned long starttime;
 
 	VERBOSE_TOROUT_STRING("torture_onoff task started");
 	for_each_online_cpu(cpu)
 		maxcpu = cpu;
 	WARN_ON(maxcpu < 0);
+
+	if (maxcpu == 0) {
+		VERBOSE_TOROUT_STRING("Only one CPU, so CPU-hotplug testing is disabled");
+		goto stop;
+	}
+
 	if (onoff_holdoff > 0) {
 		VERBOSE_TOROUT_STRING("torture_onoff begin holdoff");
 		schedule_timeout_interruptible(onoff_holdoff);
@@ -106,69 +207,16 @@ torture_onoff(void *arg)
 	}
 	while (!torture_must_stop()) {
 		cpu = (torture_random(&rand) >> 4) % (maxcpu + 1);
-		if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {
-			if (verbose)
-				pr_alert("%s" TORTURE_FLAG
-					 "torture_onoff task: offlining %d\n",
-					 torture_type, cpu);
-			starttime = jiffies;
-			n_offline_attempts++;
-			ret = cpu_down(cpu);
-			if (ret) {
-				if (verbose)
-					pr_alert("%s" TORTURE_FLAG
-						 "torture_onoff task: offline %d failed: errno %d\n",
-						 torture_type, cpu, ret);
-			} else {
-				if (verbose)
-					pr_alert("%s" TORTURE_FLAG
-						 "torture_onoff task: offlined %d\n",
-						 torture_type, cpu);
-				n_offline_successes++;
-				delta = jiffies - starttime;
-				sum_offline += delta;
-				if (min_offline < 0) {
-					min_offline = delta;
-					max_offline = delta;
-				}
-				if (min_offline > delta)
-					min_offline = delta;
-				if (max_offline < delta)
-					max_offline = delta;
-			}
-		} else if (cpu_is_hotpluggable(cpu)) {
-			if (verbose)
-				pr_alert("%s" TORTURE_FLAG
-					 "torture_onoff task: onlining %d\n",
-					 torture_type, cpu);
-			starttime = jiffies;
-			n_online_attempts++;
-			ret = cpu_up(cpu);
-			if (ret) {
-				if (verbose)
-					pr_alert("%s" TORTURE_FLAG
-						 "torture_onoff task: online %d failed: errno %d\n",
-						 torture_type, cpu, ret);
-			} else {
-				if (verbose)
-					pr_alert("%s" TORTURE_FLAG
-						 "torture_onoff task: onlined %d\n",
-						 torture_type, cpu);
-				n_online_successes++;
-				delta = jiffies - starttime;
-				sum_online += delta;
-				if (min_online < 0) {
-					min_online = delta;
-					max_online = delta;
-				}
-				if (min_online > delta)
-					min_online = delta;
-				if (max_online < delta)
-					max_online = delta;
-			}
-		}
+		if (!torture_offline(cpu,
+				     &n_offline_attempts, &n_offline_successes,
+				     &sum_offline, &min_offline, &max_offline))
+			torture_online(cpu,
+				       &n_online_attempts, &n_online_successes,
+				       &sum_online, &min_online, &max_online);
 		schedule_timeout_interruptible(onoff_interval);
 	}
+
+stop:
 	torture_kthread_stopping("torture_onoff");
 	return 0;
 }