Merge branch 'perf/core' into perf/uprobes

Merge in latest upstream (and the latest perf development tree),
to prepare for tooling changes, and also to pick up v3.4 MM
changes that the uprobes code needs to take care of.

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

1 files changed, 276 insertions, 174 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 8bb35d73e1f..c023464816b 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -25,7 +25,6 @@
  */
 
 #include <linux/delay.h>
-#include <linux/stop_machine.h>
 
 #define RCU_KTHREAD_PRIO 1
 
@@ -63,7 +62,10 @@ static void __init rcu_bootup_announce_oddness(void)
 	printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
 #endif
 #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
-	printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n");
+	printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
+#endif
+#if defined(CONFIG_RCU_CPU_STALL_INFO)
+	printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
 #endif
 #if NUM_RCU_LVL_4 != 0
 	printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
@@ -490,6 +492,31 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp)
 
 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
 
+#ifdef CONFIG_RCU_CPU_STALL_INFO
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+	printk(KERN_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)
+{
+	printk(KERN_CONT "\n");
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+}
+
+static void rcu_print_task_stall_end(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
 /*
  * Scan the current list of tasks blocked within RCU read-side critical
  * sections, printing out the tid of each.
@@ -501,12 +528,14 @@ static int rcu_print_task_stall(struct rcu_node *rnp)
 
 	if (!rcu_preempt_blocked_readers_cgp(rnp))
 		return 0;
+	rcu_print_task_stall_begin(rnp);
 	t = list_entry(rnp->gp_tasks,
 		       struct task_struct, rcu_node_entry);
 	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
-		printk(" P%d", t->pid);
+		printk(KERN_CONT " P%d", t->pid);
 		ndetected++;
 	}
+	rcu_print_task_stall_end();
 	return ndetected;
 }
 
@@ -581,7 +610,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
 	 * absolutely necessary, but this is a good performance/complexity
 	 * tradeoff.
 	 */
-	if (rcu_preempt_blocked_readers_cgp(rnp))
+	if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
 		retval |= RCU_OFL_TASKS_NORM_GP;
 	if (rcu_preempted_readers_exp(rnp))
 		retval |= RCU_OFL_TASKS_EXP_GP;
@@ -618,16 +647,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
 	return retval;
 }
 
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 /*
  * Do CPU-offline processing for preemptible RCU.
  */
-static void rcu_preempt_offline_cpu(int cpu)
+static void rcu_preempt_cleanup_dead_cpu(int cpu)
 {
-	__rcu_offline_cpu(cpu, &rcu_preempt_state);
+	rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
 }
 
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
 /*
  * Check for a quiescent state from the current CPU.  When a task blocks,
  * the task is recorded in the corresponding CPU's rcu_node structure,
@@ -671,10 +700,24 @@ static void rcu_preempt_do_callbacks(void)
  */
 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 {
-	__call_rcu(head, func, &rcu_preempt_state);
+	__call_rcu(head, func, &rcu_preempt_state, 0);
 }
 EXPORT_SYMBOL_GPL(call_rcu);
 
+/*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks.  Until then, this
+ * function may only be called from __kfree_rcu().
+ */
+void kfree_call_rcu(struct rcu_head *head,
+		    void (*func)(struct rcu_head *rcu))
+{
+	__call_rcu(head, func, &rcu_preempt_state, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
 /**
  * synchronize_rcu - wait until a grace period has elapsed.
  *
@@ -688,6 +731,10 @@ EXPORT_SYMBOL_GPL(call_rcu);
  */
 void synchronize_rcu(void)
 {
+	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+			   !lock_is_held(&rcu_lock_map) &&
+			   !lock_is_held(&rcu_sched_lock_map),
+			   "Illegal synchronize_rcu() in RCU read-side critical section");
 	if (!rcu_scheduler_active)
 		return;
 	wait_rcu_gp(call_rcu);
@@ -788,10 +835,22 @@ sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
 		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
 }
 
-/*
- * Wait for an rcu-preempt grace period, but expedite it.  The basic idea
- * is to invoke synchronize_sched_expedited() to push all the tasks to
- * the ->blkd_tasks lists and wait for this list to drain.
+/**
+ * synchronize_rcu_expedited - Brute-force RCU grace period
+ *
+ * Wait for an RCU-preempt grace period, but expedite it.  The basic
+ * idea is to invoke synchronize_sched_expedited() to push all the tasks to
+ * the ->blkd_tasks lists and wait for this list to drain.  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_rcu_expedited() in a loop,
+ * please restructure your code to batch your updates, and then Use a
+ * single synchronize_rcu() instead.
+ *
+ * Note that it is illegal to call this function while holding any lock
+ * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
+ * to call this function from a CPU-hotplug notifier.  Failing to observe
+ * these restriction will result in deadlock.
  */
 void synchronize_rcu_expedited(void)
 {
@@ -869,9 +928,9 @@ static int rcu_preempt_pending(int cpu)
 }
 
 /*
- * Does preemptible RCU need the CPU to stay out of dynticks mode?
+ * Does preemptible RCU have callbacks on this CPU?
  */
-static int rcu_preempt_needs_cpu(int cpu)
+static int rcu_preempt_cpu_has_callbacks(int cpu)
 {
 	return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
 }
@@ -894,11 +953,12 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 }
 
 /*
- * Move preemptible RCU's callbacks from dying CPU to other online CPU.
+ * Move preemptible RCU's callbacks from dying CPU to other online CPU
+ * and record a quiescent state.
  */
-static void rcu_preempt_send_cbs_to_online(void)
+static void rcu_preempt_cleanup_dying_cpu(void)
 {
-	rcu_send_cbs_to_online(&rcu_preempt_state);
+	rcu_cleanup_dying_cpu(&rcu_preempt_state);
 }
 
 /*
@@ -1034,16 +1094,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
 	return 0;
 }
 
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 /*
  * Because preemptible RCU does not exist, it never needs CPU-offline
  * processing.
  */
-static void rcu_preempt_offline_cpu(int cpu)
+static void rcu_preempt_cleanup_dead_cpu(int cpu)
 {
 }
 
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
 /*
  * Because preemptible RCU does not exist, it never has any callbacks
  * to check.
@@ -1061,6 +1121,22 @@ static void rcu_preempt_process_callbacks(void)
 }
 
 /*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks.  Until then, this
+ * function may only be called from __kfree_rcu().
+ *
+ * Because there is no preemptible RCU, we use RCU-sched instead.
+ */
+void kfree_call_rcu(struct rcu_head *head,
+		    void (*func)(struct rcu_head *rcu))
+{
+	__call_rcu(head, func, &rcu_sched_state, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
+/*
  * Wait for an rcu-preempt grace period, but make it happen quickly.
  * But because preemptible RCU does not exist, map to rcu-sched.
  */
@@ -1093,9 +1169,9 @@ static int rcu_preempt_pending(int cpu)
 }
 
 /*
- * Because preemptible RCU does not exist, it never needs any CPU.
+ * Because preemptible RCU does not exist, it never has callbacks
  */
-static int rcu_preempt_needs_cpu(int cpu)
+static int rcu_preempt_cpu_has_callbacks(int cpu)
 {
 	return 0;
 }
@@ -1119,9 +1195,9 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 }
 
 /*
- * Because there is no preemptible RCU, there are no callbacks to move.
+ * Because there is no preemptible RCU, there is no cleanup to do.
  */
-static void rcu_preempt_send_cbs_to_online(void)
+static void rcu_preempt_cleanup_dying_cpu(void)
 {
 }
 
@@ -1823,132 +1899,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
-#ifndef CONFIG_SMP
-
-void synchronize_sched_expedited(void)
-{
-	cond_resched();
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
-#else /* #ifndef CONFIG_SMP */
-
-static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
-static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
-
-static int synchronize_sched_expedited_cpu_stop(void *data)
-{
-	/*
-	 * There must be a full memory barrier on each affected CPU
-	 * between the time that try_stop_cpus() is called and the
-	 * time that it returns.
-	 *
-	 * In the current initial implementation of cpu_stop, the
-	 * above condition is already met when the control reaches
-	 * this point and the following smp_mb() is not strictly
-	 * necessary.  Do smp_mb() anyway for documentation and
-	 * robustness against future implementation changes.
-	 */
-	smp_mb(); /* See above comment block. */
-	return 0;
-}
-
-/*
- * Wait for an rcu-sched grace period to elapse, but use "big hammer"
- * approach to force grace period to end quickly.  This consumes
- * significant time on all CPUs, and is thus not recommended for
- * any sort of common-case code.
- *
- * Note that it is illegal to call this function while holding any
- * lock that is acquired by a CPU-hotplug notifier.  Failing to
- * observe this restriction will result in deadlock.
- *
- * This implementation can be thought of as an application of ticket
- * locking to RCU, with sync_sched_expedited_started and
- * sync_sched_expedited_done taking on the roles of the halves
- * of the ticket-lock word.  Each task atomically increments
- * sync_sched_expedited_started upon entry, snapshotting the old value,
- * then attempts to stop all the CPUs.  If this succeeds, then each
- * CPU will have executed a context switch, resulting in an RCU-sched
- * grace period.  We are then done, so we use atomic_cmpxchg() to
- * update sync_sched_expedited_done to match our snapshot -- but
- * only if someone else has not already advanced past our snapshot.
- *
- * On the other hand, if try_stop_cpus() fails, we check the value
- * of sync_sched_expedited_done.  If it has advanced past our
- * initial snapshot, then someone else must have forced a grace period
- * some time after we took our snapshot.  In this case, our work is
- * done for us, and we can simply return.  Otherwise, we try again,
- * but keep our initial snapshot for purposes of checking for someone
- * doing our work for us.
- *
- * If we fail too many times in a row, we fall back to synchronize_sched().
- */
-void synchronize_sched_expedited(void)
-{
-	int firstsnap, s, snap, trycount = 0;
-
-	/* Note that atomic_inc_return() implies full memory barrier. */
-	firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
-	get_online_cpus();
-
-	/*
-	 * Each pass through the following loop attempts to force a
-	 * context switch on each CPU.
-	 */
-	while (try_stop_cpus(cpu_online_mask,
-			     synchronize_sched_expedited_cpu_stop,
-			     NULL) == -EAGAIN) {
-		put_online_cpus();
-
-		/* No joy, try again later.  Or just synchronize_sched(). */
-		if (trycount++ < 10)
-			udelay(trycount * num_online_cpus());
-		else {
-			synchronize_sched();
-			return;
-		}
-
-		/* Check to see if someone else did our work for us. */
-		s = atomic_read(&sync_sched_expedited_done);
-		if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
-			smp_mb(); /* ensure test happens before caller kfree */
-			return;
-		}
-
-		/*
-		 * Refetching sync_sched_expedited_started allows later
-		 * callers to piggyback on our grace period.  We subtract
-		 * 1 to get the same token that the last incrementer got.
-		 * We retry after they started, so our grace period works
-		 * for them, and they started after our first try, so their
-		 * grace period works for us.
-		 */
-		get_online_cpus();
-		snap = atomic_read(&sync_sched_expedited_started);
-		smp_mb(); /* ensure read is before try_stop_cpus(). */
-	}
-
-	/*
-	 * Everyone up to our most recent fetch is covered by our grace
-	 * period.  Update the counter, but only if our work is still
-	 * relevant -- which it won't be if someone who started later
-	 * than we did beat us to the punch.
-	 */
-	do {
-		s = atomic_read(&sync_sched_expedited_done);
-		if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
-			smp_mb(); /* ensure test happens before caller kfree */
-			break;
-		}
-	} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
-
-	put_online_cpus();
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
-#endif /* #else #ifndef CONFIG_SMP */
-
 #if !defined(CONFIG_RCU_FAST_NO_HZ)
 
 /*
@@ -1981,7 +1931,7 @@ static void rcu_cleanup_after_idle(int cpu)
 }
 
 /*
- * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=y,
+ * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
  * is nothing.
  */
 static void rcu_prepare_for_idle(int cpu)
@@ -2015,6 +1965,9 @@ static void rcu_prepare_for_idle(int cpu)
  *	number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
  *	system.  And if you are -that- concerned about energy efficiency,
  *	just power the system down and be done with it!
+ * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
+ *	permitted to sleep in dyntick-idle mode with only lazy RCU
+ *	callbacks pending.  Setting this too high can OOM your system.
  *
  * The values below work well in practice.  If future workloads require
  * adjustment, they can be converted into kernel config parameters, though
@@ -2023,11 +1976,13 @@ static void rcu_prepare_for_idle(int cpu)
 #define RCU_IDLE_FLUSHES 5		/* Number of dyntick-idle tries. */
 #define RCU_IDLE_OPT_FLUSHES 3		/* Optional dyntick-idle tries. */
 #define RCU_IDLE_GP_DELAY 6		/* Roughly one grace period. */
+#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
 
 static DEFINE_PER_CPU(int, rcu_dyntick_drain);
 static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
 static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer);
-static ktime_t rcu_idle_gp_wait;
+static ktime_t rcu_idle_gp_wait;	/* If some non-lazy callbacks. */
+static ktime_t rcu_idle_lazy_gp_wait;	/* If only lazy callbacks. */
 
 /*
  * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
@@ -2048,6 +2003,48 @@ int rcu_needs_cpu(int cpu)
 }
 
 /*
+ * Does the specified flavor of RCU have non-lazy callbacks pending on
+ * the specified CPU?  Both RCU flavor and CPU are specified by the
+ * rcu_data structure.
+ */
+static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
+{
+	return rdp->qlen != rdp->qlen_lazy;
+}
+
+#ifdef CONFIG_TREE_PREEMPT_RCU
+
+/*
+ * Are there non-lazy RCU-preempt callbacks?  (There cannot be if there
+ * is no RCU-preempt in the kernel.)
+ */
+static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
+{
+	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
+
+	return __rcu_cpu_has_nonlazy_callbacks(rdp);
+}
+
+#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
+{
+	return 0;
+}
+
+#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+/*
+ * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
+ */
+static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
+{
+	return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
+	       __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
+	       rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
+}
+
+/*
  * Timer handler used to force CPU to start pushing its remaining RCU
  * callbacks in the case where it entered dyntick-idle mode with callbacks
  * pending.  The hander doesn't really need to do anything because the
@@ -2074,6 +2071,8 @@ static void rcu_prepare_for_idle_init(int cpu)
 		unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY);
 
 		rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000);
+		upj = jiffies_to_usecs(RCU_IDLE_LAZY_GP_DELAY);
+		rcu_idle_lazy_gp_wait = ns_to_ktime(upj * (u64)1000);
 		firsttime = 0;
 	}
 }
@@ -2109,10 +2108,6 @@ static void rcu_cleanup_after_idle(int cpu)
  */
 static void rcu_prepare_for_idle(int cpu)
 {
-	unsigned long flags;
-
-	local_irq_save(flags);
-
 	/*
 	 * If there are no callbacks on this CPU, enter dyntick-idle mode.
 	 * Also reset state to avoid prejudicing later attempts.
@@ -2120,7 +2115,6 @@ static void rcu_prepare_for_idle(int cpu)
 	if (!rcu_cpu_has_callbacks(cpu)) {
 		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
 		per_cpu(rcu_dyntick_drain, cpu) = 0;
-		local_irq_restore(flags);
 		trace_rcu_prep_idle("No callbacks");
 		return;
 	}
@@ -2130,7 +2124,6 @@ static void rcu_prepare_for_idle(int cpu)
 	 * refrained from disabling the scheduling-clock tick.
 	 */
 	if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) {
-		local_irq_restore(flags);
 		trace_rcu_prep_idle("In holdoff");
 		return;
 	}
@@ -2140,18 +2133,22 @@ static void rcu_prepare_for_idle(int cpu)
 		/* First time through, initialize the counter. */
 		per_cpu(rcu_dyntick_drain, cpu) = RCU_IDLE_FLUSHES;
 	} else if (per_cpu(rcu_dyntick_drain, cpu) <= RCU_IDLE_OPT_FLUSHES &&
-		   !rcu_pending(cpu)) {
+		   !rcu_pending(cpu) &&
+		   !local_softirq_pending()) {
 		/* Can we go dyntick-idle despite still having callbacks? */
 		trace_rcu_prep_idle("Dyntick with callbacks");
 		per_cpu(rcu_dyntick_drain, cpu) = 0;
-		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
-		hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
-			      rcu_idle_gp_wait, HRTIMER_MODE_REL);
+		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
+		if (rcu_cpu_has_nonlazy_callbacks(cpu))
+			hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
+				      rcu_idle_gp_wait, HRTIMER_MODE_REL);
+		else
+			hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
+				      rcu_idle_lazy_gp_wait, HRTIMER_MODE_REL);
 		return; /* Nothing more to do immediately. */
 	} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
 		/* We have hit the limit, so time to give up. */
 		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
-		local_irq_restore(flags);
 		trace_rcu_prep_idle("Begin holdoff");
 		invoke_rcu_core();  /* Force the CPU out of dyntick-idle. */
 		return;
@@ -2163,23 +2160,17 @@ static void rcu_prepare_for_idle(int cpu)
 	 */
 #ifdef CONFIG_TREE_PREEMPT_RCU
 	if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
-		local_irq_restore(flags);
 		rcu_preempt_qs(cpu);
 		force_quiescent_state(&rcu_preempt_state, 0);
-		local_irq_save(flags);
 	}
 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 	if (per_cpu(rcu_sched_data, cpu).nxtlist) {
-		local_irq_restore(flags);
 		rcu_sched_qs(cpu);
 		force_quiescent_state(&rcu_sched_state, 0);
-		local_irq_save(flags);
 	}
 	if (per_cpu(rcu_bh_data, cpu).nxtlist) {
-		local_irq_restore(flags);
 		rcu_bh_qs(cpu);
 		force_quiescent_state(&rcu_bh_state, 0);
-		local_irq_save(flags);
 	}
 
 	/*
@@ -2187,13 +2178,124 @@ static void rcu_prepare_for_idle(int cpu)
 	 * So try forcing the callbacks through the grace period.
 	 */
 	if (rcu_cpu_has_callbacks(cpu)) {
-		local_irq_restore(flags);
 		trace_rcu_prep_idle("More callbacks");
 		invoke_rcu_core();
-	} else {
-		local_irq_restore(flags);
+	} else
 		trace_rcu_prep_idle("Callbacks drained");
-	}
 }
 
 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+#ifdef CONFIG_RCU_CPU_STALL_INFO
+
+#ifdef CONFIG_RCU_FAST_NO_HZ
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+	struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);
+
+	sprintf(cp, "drain=%d %c timer=%lld",
+		per_cpu(rcu_dyntick_drain, cpu),
+		per_cpu(rcu_dyntick_holdoff, cpu) == jiffies ? 'H' : '.',
+		hrtimer_active(hrtp)
+			? ktime_to_us(hrtimer_get_remaining(hrtp))
+			: -1);
+}
+
+#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+/* Initiate the stall-info list. */
+static void print_cpu_stall_info_begin(void)
+{
+	printk(KERN_CONT "\n");
+}
+
+/*
+ * Print out diagnostic information for the specified stalled CPU.
+ *
+ * If the specified CPU is aware of the current RCU grace period
+ * (flavor specified by rsp), 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(struct rcu_state *rsp, int cpu)
+{
+	char fast_no_hz[72];
+	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+	struct rcu_dynticks *rdtp = rdp->dynticks;
+	char *ticks_title;
+	unsigned long ticks_value;
+
+	if (rsp->gpnum == rdp->gpnum) {
+		ticks_title = "ticks this GP";
+		ticks_value = rdp->ticks_this_gp;
+	} else {
+		ticks_title = "GPs behind";
+		ticks_value = rsp->gpnum - rdp->gpnum;
+	}
+	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
+	printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
+	       cpu, ticks_value, ticks_title,
+	       atomic_read(&rdtp->dynticks) & 0xfff,
+	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
+	       fast_no_hz);
+}
+
+/* Terminate the stall-info list. */
+static void print_cpu_stall_info_end(void)
+{
+	printk(KERN_ERR "\t");
+}
+
+/* Zero ->ticks_this_gp for all flavors of RCU. */
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+	rdp->ticks_this_gp = 0;
+}
+
+/* Increment ->ticks_this_gp for all flavors of RCU. */
+static void increment_cpu_stall_ticks(void)
+{
+	__get_cpu_var(rcu_sched_data).ticks_this_gp++;
+	__get_cpu_var(rcu_bh_data).ticks_this_gp++;
+#ifdef CONFIG_TREE_PREEMPT_RCU
+	__get_cpu_var(rcu_preempt_data).ticks_this_gp++;
+#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+static void print_cpu_stall_info_begin(void)
+{
+	printk(KERN_CONT " {");
+}
+
+static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
+{
+	printk(KERN_CONT " %d", cpu);
+}
+
+static void print_cpu_stall_info_end(void)
+{
+	printk(KERN_CONT "} ");
+}
+
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+}
+
+static void increment_cpu_stall_ticks(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */