Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull the v3.5 RCU tree from Paul E. McKenney:

 1)	A set of improvements and fixes to the RCU_FAST_NO_HZ feature
	(with more on the way for 3.6).  Posted to LKML:
	https://lkml.org/lkml/2012/4/23/324 (commits 1-3 and 5),
	https://lkml.org/lkml/2012/4/16/611 (commit 4),
	https://lkml.org/lkml/2012/4/30/390 (commit 6), and
	https://lkml.org/lkml/2012/5/4/410 (commit 7, combined with
	the other commits for the convenience of the tester).

 2)	Changes to make rcu_barrier() avoid disrupting execution of CPUs
	that have no RCU callbacks.  Posted to LKML:
	https://lkml.org/lkml/2012/4/23/322.

 3)	A couple of commits that improve the efficiency of the interaction
	between preemptible RCU and the scheduler, these two being all
	that survived an abortive attempt to allow preemptible RCU's
	__rcu_read_lock() to be inlined.  The full set was posted to
	LKML at https://lkml.org/lkml/2012/4/14/143, and the first and
	third patches of that set remain.

 4)	Lai Jiangshan's algorithmic implementation of SRCU, which includes
	call_srcu() and srcu_barrier().  A major feature of this new
	implementation is that synchronize_srcu() no longer disturbs
	the execution of other CPUs.  This work is based on earlier
	implementations by Peter Zijlstra and Paul E. McKenney.  Posted to
	LKML: https://lkml.org/lkml/2012/2/22/82.

 5)	A number of miscellaneous bug fixes and improvements which were
	posted to LKML at: https://lkml.org/lkml/2012/4/23/353 with
	subsequent updates posted to LKML.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 244 insertions, 88 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d0c5baf1ab1..0da7b88d92d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -75,6 +75,8 @@ static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
 	.gpnum = -300, \
 	.completed = -300, \
 	.onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.onofflock), \
+	.orphan_nxttail = &structname##_state.orphan_nxtlist, \
+	.orphan_donetail = &structname##_state.orphan_donelist, \
 	.fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.fqslock), \
 	.n_force_qs = 0, \
 	.n_force_qs_ngp = 0, \
@@ -145,6 +147,13 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
 unsigned long rcutorture_testseq;
 unsigned long rcutorture_vernum;
 
+/* State information for rcu_barrier() and friends. */
+
+static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
+static atomic_t rcu_barrier_cpu_count;
+static DEFINE_MUTEX(rcu_barrier_mutex);
+static struct completion rcu_barrier_completion;
+
 /*
  * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
  * permit this function to be invoked without holding the root rcu_node
@@ -192,7 +201,6 @@ void rcu_note_context_switch(int cpu)
 {
 	trace_rcu_utilization("Start context switch");
 	rcu_sched_qs(cpu);
-	rcu_preempt_note_context_switch(cpu);
 	trace_rcu_utilization("End context switch");
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
@@ -1311,95 +1319,133 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
 #ifdef CONFIG_HOTPLUG_CPU
 
 /*
- * Move a dying CPU's RCU callbacks to online CPU's callback list.
- * Also record a quiescent state for this CPU for the current grace period.
- * Synchronization and interrupt disabling are not required because
- * this function executes in stop_machine() context.  Therefore, cleanup
- * operations that might block must be done later from the CPU_DEAD
- * notifier.
- *
- * Note that the outgoing CPU's bit has already been cleared in the
- * cpu_online_mask.  This allows us to randomly pick a callback
- * destination from the bits set in that mask.
+ * Send the specified CPU's RCU callbacks to the orphanage.  The
+ * specified CPU must be offline, and the caller must hold the
+ * ->onofflock.
  */
-static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
+static void
+rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
+			  struct rcu_node *rnp, struct rcu_data *rdp)
 {
 	int i;
-	unsigned long mask;
-	int receive_cpu = cpumask_any(cpu_online_mask);
-	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
-	struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
-	RCU_TRACE(struct rcu_node *rnp = rdp->mynode); /* For dying CPU. */
 
-	/* First, adjust the counts. */
+	/*
+	 * Orphan the callbacks.  First adjust the counts.  This is safe
+	 * because ->onofflock excludes _rcu_barrier()'s adoption of
+	 * the callbacks, thus no memory barrier is required.
+	 */
 	if (rdp->nxtlist != NULL) {
-		receive_rdp->qlen_lazy += rdp->qlen_lazy;
-		receive_rdp->qlen += rdp->qlen;
+		rsp->qlen_lazy += rdp->qlen_lazy;
+		rsp->qlen += rdp->qlen;
+		rdp->n_cbs_orphaned += rdp->qlen;
 		rdp->qlen_lazy = 0;
 		rdp->qlen = 0;
 	}
 
 	/*
-	 * Next, move ready-to-invoke callbacks to be invoked on some
-	 * other CPU.  These will not be required to pass through another
-	 * grace period:  They are done, regardless of CPU.
+	 * Next, move those callbacks still needing a grace period to
+	 * the orphanage, where some other CPU will pick them up.
+	 * Some of the callbacks might have gone partway through a grace
+	 * period, but that is too bad.  They get to start over because we
+	 * cannot assume that grace periods are synchronized across CPUs.
+	 * We don't bother updating the ->nxttail[] array yet, instead
+	 * we just reset the whole thing later on.
 	 */
-	if (rdp->nxtlist != NULL &&
-	    rdp->nxttail[RCU_DONE_TAIL] != &rdp->nxtlist) {
-		struct rcu_head *oldhead;
-		struct rcu_head **oldtail;
-		struct rcu_head **newtail;
-
-		oldhead = rdp->nxtlist;
-		oldtail = receive_rdp->nxttail[RCU_DONE_TAIL];
-		rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
-		*rdp->nxttail[RCU_DONE_TAIL] = *oldtail;
-		*receive_rdp->nxttail[RCU_DONE_TAIL] = oldhead;
-		newtail = rdp->nxttail[RCU_DONE_TAIL];
-		for (i = RCU_DONE_TAIL; i < RCU_NEXT_SIZE; i++) {
-			if (receive_rdp->nxttail[i] == oldtail)
-				receive_rdp->nxttail[i] = newtail;
-			if (rdp->nxttail[i] == newtail)
-				rdp->nxttail[i] = &rdp->nxtlist;
-		}
+	if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
+		*rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
+		rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
+		*rdp->nxttail[RCU_DONE_TAIL] = NULL;
 	}
 
 	/*
-	 * Finally, put the rest of the callbacks at the end of the list.
-	 * The ones that made it partway through get to start over:  We
-	 * cannot assume that grace periods are synchronized across CPUs.
-	 * (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but
-	 * this does not seem compelling.  Not yet, anyway.)
+	 * Then move the ready-to-invoke callbacks to the orphanage,
+	 * where some other CPU will pick them up.  These will not be
+	 * required to pass though another grace period: They are done.
 	 */
 	if (rdp->nxtlist != NULL) {
-		*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
-		receive_rdp->nxttail[RCU_NEXT_TAIL] =
-				rdp->nxttail[RCU_NEXT_TAIL];
-		receive_rdp->n_cbs_adopted += rdp->qlen;
-		rdp->n_cbs_orphaned += rdp->qlen;
-
-		rdp->nxtlist = NULL;
-		for (i = 0; i < RCU_NEXT_SIZE; i++)
-			rdp->nxttail[i] = &rdp->nxtlist;
+		*rsp->orphan_donetail = rdp->nxtlist;
+		rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
 	}
 
+	/* Finally, initialize the rcu_data structure's list to empty.  */
+	rdp->nxtlist = NULL;
+	for (i = 0; i < RCU_NEXT_SIZE; i++)
+		rdp->nxttail[i] = &rdp->nxtlist;
+}
+
+/*
+ * Adopt the RCU callbacks from the specified rcu_state structure's
+ * orphanage.  The caller must hold the ->onofflock.
+ */
+static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
+{
+	int i;
+	struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
+
 	/*
-	 * Record a quiescent state for the dying CPU.  This is safe
-	 * only because we have already cleared out the callbacks.
-	 * (Otherwise, the RCU core might try to schedule the invocation
-	 * of callbacks on this now-offline CPU, which would be bad.)
+	 * If there is an rcu_barrier() operation in progress, then
+	 * only the task doing that operation is permitted to adopt
+	 * callbacks.  To do otherwise breaks rcu_barrier() and friends
+	 * by causing them to fail to wait for the callbacks in the
+	 * orphanage.
 	 */
-	mask = rdp->grpmask;	/* rnp->grplo is constant. */
+	if (rsp->rcu_barrier_in_progress &&
+	    rsp->rcu_barrier_in_progress != current)
+		return;
+
+	/* Do the accounting first. */
+	rdp->qlen_lazy += rsp->qlen_lazy;
+	rdp->qlen += rsp->qlen;
+	rdp->n_cbs_adopted += rsp->qlen;
+	rsp->qlen_lazy = 0;
+	rsp->qlen = 0;
+
+	/*
+	 * We do not need a memory barrier here because the only way we
+	 * can get here if there is an rcu_barrier() in flight is if
+	 * we are the task doing the rcu_barrier().
+	 */
+
+	/* First adopt the ready-to-invoke callbacks. */
+	if (rsp->orphan_donelist != NULL) {
+		*rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
+		*rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
+		for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
+			if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
+				rdp->nxttail[i] = rsp->orphan_donetail;
+		rsp->orphan_donelist = NULL;
+		rsp->orphan_donetail = &rsp->orphan_donelist;
+	}
+
+	/* And then adopt the callbacks that still need a grace period. */
+	if (rsp->orphan_nxtlist != NULL) {
+		*rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
+		rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
+		rsp->orphan_nxtlist = NULL;
+		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+	}
+}
+
+/*
+ * Trace the fact that this CPU is going offline.
+ */
+static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
+{
+	RCU_TRACE(unsigned long mask);
+	RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
+	RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
+
+	RCU_TRACE(mask = rdp->grpmask);
 	trace_rcu_grace_period(rsp->name,
 			       rnp->gpnum + 1 - !!(rnp->qsmask & mask),
 			       "cpuofl");
-	rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
-	/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
 }
 
 /*
  * The CPU has been completely removed, and some other CPU is reporting
- * this fact from process context.  Do the remainder of the cleanup.
+ * this fact from process context.  Do the remainder of the cleanup,
+ * including orphaning the outgoing CPU's RCU callbacks, and also
+ * adopting them, if there is no _rcu_barrier() instance running.
  * There can only be one CPU hotplug operation at a time, so no other
  * CPU can be attempting to update rcu_cpu_kthread_task.
  */
@@ -1409,17 +1455,21 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 	unsigned long mask;
 	int need_report = 0;
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
-	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rnp. */
+	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
 	/* Adjust any no-longer-needed kthreads. */
 	rcu_stop_cpu_kthread(cpu);
 	rcu_node_kthread_setaffinity(rnp, -1);
 
-	/* Remove the dying CPU from the bitmasks in the rcu_node hierarchy. */
+	/* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
 
 	/* Exclude any attempts to start a new grace period. */
 	raw_spin_lock_irqsave(&rsp->onofflock, flags);
 
+	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
+	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
+	rcu_adopt_orphan_cbs(rsp);
+
 	/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
 	mask = rdp->grpmask;	/* rnp->grplo is constant. */
 	do {
@@ -1456,6 +1506,10 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
 
+static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
+{
+}
+
 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
 {
 }
@@ -1524,9 +1578,6 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 			    rcu_is_callbacks_kthread());
 
 	/* Update count, and requeue any remaining callbacks. */
-	rdp->qlen_lazy -= count_lazy;
-	rdp->qlen -= count;
-	rdp->n_cbs_invoked += count;
 	if (list != NULL) {
 		*tail = rdp->nxtlist;
 		rdp->nxtlist = list;
@@ -1536,6 +1587,10 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 			else
 				break;
 	}
+	smp_mb(); /* List handling before counting for rcu_barrier(). */
+	rdp->qlen_lazy -= count_lazy;
+	rdp->qlen -= count;
+	rdp->n_cbs_invoked += count;
 
 	/* Reinstate batch limit if we have worked down the excess. */
 	if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
@@ -1823,11 +1878,14 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
 	rdp = this_cpu_ptr(rsp->rda);
 
 	/* Add the callback to our list. */
-	*rdp->nxttail[RCU_NEXT_TAIL] = head;
-	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
 	rdp->qlen++;
 	if (lazy)
 		rdp->qlen_lazy++;
+	else
+		rcu_idle_count_callbacks_posted();
+	smp_mb();  /* Count before adding callback for rcu_barrier(). */
+	*rdp->nxttail[RCU_NEXT_TAIL] = head;
+	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
 
 	if (__is_kfree_rcu_offset((unsigned long)func))
 		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
@@ -1893,6 +1951,38 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 }
 EXPORT_SYMBOL_GPL(call_rcu_bh);
 
+/*
+ * Because a context switch is a grace period for RCU-sched and RCU-bh,
+ * any blocking grace-period wait automatically implies a grace period
+ * if there is only one CPU online at any point time during execution
+ * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
+ * occasionally incorrectly indicate that there are multiple CPUs online
+ * when there was in fact only one the whole time, as this just adds
+ * some overhead: RCU still operates correctly.
+ *
+ * Of course, sampling num_online_cpus() with preemption enabled can
+ * give erroneous results if there are concurrent CPU-hotplug operations.
+ * For example, given a demonic sequence of preemptions in num_online_cpus()
+ * and CPU-hotplug operations, there could be two or more CPUs online at
+ * all times, but num_online_cpus() might well return one (or even zero).
+ *
+ * However, all such demonic sequences require at least one CPU-offline
+ * operation.  Furthermore, rcu_blocking_is_gp() giving the wrong answer
+ * is only a problem if there is an RCU read-side critical section executing
+ * throughout.  But RCU-sched and RCU-bh read-side critical sections
+ * disable either preemption or bh, which prevents a CPU from going offline.
+ * Therefore, the only way that rcu_blocking_is_gp() can incorrectly return
+ * that there is only one CPU when in fact there was more than one throughout
+ * is when there were no RCU readers in the system.  If there are no
+ * RCU readers, the grace period by definition can be of zero length,
+ * regardless of the number of online CPUs.
+ */
+static inline int rcu_blocking_is_gp(void)
+{
+	might_sleep();  /* Check for RCU read-side critical section. */
+	return num_online_cpus() <= 1;
+}
+
 /**
  * synchronize_sched - wait until an rcu-sched grace period has elapsed.
  *
@@ -2166,11 +2256,10 @@ static int rcu_cpu_has_callbacks(int cpu)
 	       rcu_preempt_cpu_has_callbacks(cpu);
 }
 
-static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
-static atomic_t rcu_barrier_cpu_count;
-static DEFINE_MUTEX(rcu_barrier_mutex);
-static struct completion rcu_barrier_completion;
-
+/*
+ * RCU callback function for _rcu_barrier().  If we are last, wake
+ * up the task executing _rcu_barrier().
+ */
 static void rcu_barrier_callback(struct rcu_head *notused)
 {
 	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
@@ -2200,27 +2289,94 @@ static void _rcu_barrier(struct rcu_state *rsp,
 			 void (*call_rcu_func)(struct rcu_head *head,
 					       void (*func)(struct rcu_head *head)))
 {
-	BUG_ON(in_interrupt());
+	int cpu;
+	unsigned long flags;
+	struct rcu_data *rdp;
+	struct rcu_head rh;
+
+	init_rcu_head_on_stack(&rh);
+
 	/* Take mutex to serialize concurrent rcu_barrier() requests. */
 	mutex_lock(&rcu_barrier_mutex);
-	init_completion(&rcu_barrier_completion);
+
+	smp_mb();  /* Prevent any prior operations from leaking in. */
+
 	/*
-	 * Initialize rcu_barrier_cpu_count to 1, then invoke
-	 * rcu_barrier_func() on each CPU, so that each CPU also has
-	 * incremented rcu_barrier_cpu_count.  Only then is it safe to
-	 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
-	 * might complete its grace period before all of the other CPUs
-	 * did their increment, causing this function to return too
-	 * early.  Note that on_each_cpu() disables irqs, which prevents
-	 * any CPUs from coming online or going offline until each online
-	 * CPU has queued its RCU-barrier callback.
+	 * Initialize the count to one rather than to zero in order to
+	 * avoid a too-soon return to zero in case of a short grace period
+	 * (or preemption of this task).  Also flag this task as doing
+	 * an rcu_barrier().  This will prevent anyone else from adopting
+	 * orphaned callbacks, which could cause otherwise failure if a
+	 * CPU went offline and quickly came back online.  To see this,
+	 * consider the following sequence of events:
+	 *
+	 * 1.	We cause CPU 0 to post an rcu_barrier_callback() callback.
+	 * 2.	CPU 1 goes offline, orphaning its callbacks.
+	 * 3.	CPU 0 adopts CPU 1's orphaned callbacks.
+	 * 4.	CPU 1 comes back online.
+	 * 5.	We cause CPU 1 to post an rcu_barrier_callback() callback.
+	 * 6.	Both rcu_barrier_callback() callbacks are invoked, awakening
+	 *	us -- but before CPU 1's orphaned callbacks are invoked!!!
 	 */
+	init_completion(&rcu_barrier_completion);
 	atomic_set(&rcu_barrier_cpu_count, 1);
-	on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
+	raw_spin_lock_irqsave(&rsp->onofflock, flags);
+	rsp->rcu_barrier_in_progress = current;
+	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
+
+	/*
+	 * Force every CPU with callbacks to register a new callback
+	 * that will tell us when all the preceding callbacks have
+	 * been invoked.  If an offline CPU has callbacks, wait for
+	 * it to either come back online or to finish orphaning those
+	 * callbacks.
+	 */
+	for_each_possible_cpu(cpu) {
+		preempt_disable();
+		rdp = per_cpu_ptr(rsp->rda, cpu);
+		if (cpu_is_offline(cpu)) {
+			preempt_enable();
+			while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen))
+				schedule_timeout_interruptible(1);
+		} else if (ACCESS_ONCE(rdp->qlen)) {
+			smp_call_function_single(cpu, rcu_barrier_func,
+						 (void *)call_rcu_func, 1);
+			preempt_enable();
+		} else {
+			preempt_enable();
+		}
+	}
+
+	/*
+	 * Now that all online CPUs have rcu_barrier_callback() callbacks
+	 * posted, we can adopt all of the orphaned callbacks and place
+	 * an rcu_barrier_callback() callback after them.  When that is done,
+	 * we are guaranteed to have an rcu_barrier_callback() callback
+	 * following every callback that could possibly have been
+	 * registered before _rcu_barrier() was called.
+	 */
+	raw_spin_lock_irqsave(&rsp->onofflock, flags);
+	rcu_adopt_orphan_cbs(rsp);
+	rsp->rcu_barrier_in_progress = NULL;
+	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
+	atomic_inc(&rcu_barrier_cpu_count);
+	smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */
+	call_rcu_func(&rh, rcu_barrier_callback);
+
+	/*
+	 * Now that we have an rcu_barrier_callback() callback on each
+	 * CPU, and thus each counted, remove the initial count.
+	 */
 	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 		complete(&rcu_barrier_completion);
+
+	/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
 	wait_for_completion(&rcu_barrier_completion);
+
+	/* Other rcu_barrier() invocations can now safely proceed. */
 	mutex_unlock(&rcu_barrier_mutex);
+
+	destroy_rcu_head_on_stack(&rh);
 }
 
 /**
@@ -2417,7 +2573,7 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
 
 	for (i = NUM_RCU_LVLS - 1; i > 0; i--)
 		rsp->levelspread[i] = CONFIG_RCU_FANOUT;
-	rsp->levelspread[0] = RCU_FANOUT_LEAF;
+	rsp->levelspread[0] = CONFIG_RCU_FANOUT_LEAF;
 }
 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
 static void __init rcu_init_levelspread(struct rcu_state *rsp)