[PATCH tip/core/rcu 0/12] TINY_RCU changes for 3.11

[PATCH tip/core/rcu 0/12] TINY_RCU changes for 3.11

[Paul E. McKenney]

Hello!

This series removes TINY_PREEMPT_RCU, as promised/threatened at
http://lwn.net/Articles/541037/ and https://lkml.org/lkml/2012/11/12/545.

1.	Remove TINY_PREEMPT_RCU.  This is a straight syntactic removal,
	with no attempt at cleanup.  The remaining patches do the cleanup.

2.	Inline the now-empty show_tiny_preempt_stats() function.

3.	Inline the now-empty rcu_preempt_check_callbacks() function.

4.	Inline the now-empty rcu_preempt_remove_callbacks() function.

5.	Inline the now-empty rcu_preempt_process_callbacks() function.

6.	Because TINY_RCU no longer has kthreads, remove the code that
	used to abstract away kthread vs. softirq invocation.

7.	Inline the now-empty check_cpu_stall_preempt() function.

8.	Remove CONFIG_TINY_RCU ifdefs from include/linux/rcutiny.h

9.	Inline the now-empty rcu_preempt_note_context_switch() function.

10.	Move code to allow consolidating ifdefs in kernel/rcutiny_plugin.h.

11.	Remove TINY_PREEMPT_RCU's tracing formats from documentation.

12.	Shrink TINY_RCU a bit by moving exit_rcu() to TREE_RCU, leaving
	TINY_RCU with a static inline empty function.

							Thanx, Paul


 b/Documentation/RCU/trace.txt |  100 ----
 b/include/linux/hardirq.h     |    2 
 b/include/linux/rcupdate.h    |    5 
 b/include/linux/rcutiny.h     |   41 -
 b/include/linux/rcutree.h     |    3 
 b/init/Kconfig                |   10 
 b/kernel/rcupdate.c           |   26 -
 b/kernel/rcutiny.c            |   17 
 b/kernel/rcutiny_plugin.h     | 1017 +-----------------------------------------
 b/kernel/rcutree_plugin.h     |   26 +
 10 files changed, 90 insertions(+), 1157 deletions(-)

[PATCH tip/core/rcu 01/12] rcu: Remove TINY_PREEMPT_RCU

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

TINY_PREEMPT_RCU adds significant code and complexity, but does not
offer commensurate benefits.  People currently using TINY_PREEMPT_RCU
can get much better memory footprint with TINY_RCU, or, if they really
need preemptible RCU, they can use TREE_PREEMPT_RCU with a relatively
minor degradation in memory footprint.  Please note that this move
has been widely publicized on LKML (https://lkml.org/lkml/2012/11/12/545)
and on LWN (http://lwn.net/Articles/541037/).

This commit therefore removes TINY_PREEMPT_RCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/hardirq.h  |   2 +-
 include/linux/rcupdate.h |   2 +-
 init/Kconfig             |  10 +-
 kernel/rcutiny_plugin.h  | 854 -----------------------------------------------
 4 files changed, 3 insertions(+), 865 deletions(-)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index c1d6555..05bcc09 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -128,7 +128,7 @@ extern void synchronize_irq(unsigned int irq);
 # define synchronize_irq(irq)	barrier()
 #endif
 
-#if defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
+#if defined(CONFIG_TINY_RCU)
 
 static inline void rcu_nmi_enter(void)
 {
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 9ed2c9a..0a8276d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -277,7 +277,7 @@ void wait_rcu_gp(call_rcu_func_t crf);
 
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 #include <linux/rcutree.h>
-#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
+#elif defined(CONFIG_TINY_RCU)
 #include <linux/rcutiny.h>
 #else
 #error "Unknown RCU implementation specified to kernel configuration"
diff --git a/init/Kconfig b/init/Kconfig
index a3a2304..406b1a5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -462,18 +462,10 @@ config TINY_RCU
 	  is not required.  This option greatly reduces the
 	  memory footprint of RCU.
 
-config TINY_PREEMPT_RCU
-	bool "Preemptible UP-only small-memory-footprint RCU"
-	depends on PREEMPT && !SMP
-	help
-	  This option selects the RCU implementation that is designed
-	  for real-time UP systems.  This option greatly reduces the
-	  memory footprint of RCU.
-
 endchoice
 
 config PREEMPT_RCU
-	def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )
+	def_bool TREE_PREEMPT_RCU
 	help
 	  This option enables preemptible-RCU code that is common between
 	  the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 8a23300..29a4dd7 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -102,763 +102,6 @@ static void check_cpu_stalls(void)
 	RCU_TRACE(check_cpu_stall_preempt());
 }
 
-#ifdef CONFIG_TINY_PREEMPT_RCU
-
-#include <linux/delay.h>
-
-/* Global control variables for preemptible RCU. */
-struct rcu_preempt_ctrlblk {
-	struct rcu_ctrlblk rcb;	/* curtail: ->next ptr of last CB for GP. */
-	struct rcu_head **nexttail;
-				/* Tasks blocked in a preemptible RCU */
-				/*  read-side critical section while an */
-				/*  preemptible-RCU grace period is in */
-				/*  progress must wait for a later grace */
-				/*  period.  This pointer points to the */
-				/*  ->next pointer of the last task that */
-				/*  must wait for a later grace period, or */
-				/*  to &->rcb.rcucblist if there is no */
-				/*  such task. */
-	struct list_head blkd_tasks;
-				/* Tasks blocked in RCU read-side critical */
-				/*  section.  Tasks are placed at the head */
-				/*  of this list and age towards the tail. */
-	struct list_head *gp_tasks;
-				/* Pointer to the first task blocking the */
-				/*  current grace period, or NULL if there */
-				/*  is no such task. */
-	struct list_head *exp_tasks;
-				/* Pointer to first task blocking the */
-				/*  current expedited grace period, or NULL */
-				/*  if there is no such task.  If there */
-				/*  is no current expedited grace period, */
-				/*  then there cannot be any such task. */
-#ifdef CONFIG_RCU_BOOST
-	struct list_head *boost_tasks;
-				/* Pointer to first task that needs to be */
-				/*  priority-boosted, or NULL if no priority */
-				/*  boosting is needed.  If there is no */
-				/*  current or expedited grace period, there */
-				/*  can be no such task. */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-	u8 gpnum;		/* Current grace period. */
-	u8 gpcpu;		/* Last grace period blocked by the CPU. */
-	u8 completed;		/* Last grace period completed. */
-				/*  If all three are equal, RCU is idle. */
-#ifdef CONFIG_RCU_BOOST
-	unsigned long boost_time; /* When to start boosting (jiffies) */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-#ifdef CONFIG_RCU_TRACE
-	unsigned long n_grace_periods;
-#ifdef CONFIG_RCU_BOOST
-	unsigned long n_tasks_boosted;
-				/* Total number of tasks boosted. */
-	unsigned long n_exp_boosts;
-				/* Number of tasks boosted for expedited GP. */
-	unsigned long n_normal_boosts;
-				/* Number of tasks boosted for normal GP. */
-	unsigned long n_balk_blkd_tasks;
-				/* Refused to boost: no blocked tasks. */
-	unsigned long n_balk_exp_gp_tasks;
-				/* Refused to boost: nothing blocking GP. */
-	unsigned long n_balk_boost_tasks;
-				/* Refused to boost: already boosting. */
-	unsigned long n_balk_notyet;
-				/* Refused to boost: not yet time. */
-	unsigned long n_balk_nos;
-				/* Refused to boost: not sure why, though. */
-				/*  This can happen due to race conditions. */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-#endif /* #ifdef CONFIG_RCU_TRACE */
-};
-
-static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
-	.rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
-	.rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
-	.nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
-	.blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
-	RCU_TRACE(.rcb.name = "rcu_preempt")
-};
-
-static int rcu_preempted_readers_exp(void);
-static void rcu_report_exp_done(void);
-
-/*
- * Return true if the CPU has not yet responded to the current grace period.
- */
-static int rcu_cpu_blocking_cur_gp(void)
-{
-	return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
-}
-
-/*
- * Check for a running RCU reader.  Because there is only one CPU,
- * there can be but one running RCU reader at a time.  ;-)
- *
- * Returns zero if there are no running readers.  Returns a positive
- * number if there is at least one reader within its RCU read-side
- * critical section.  Returns a negative number if an outermost reader
- * is in the midst of exiting from its RCU read-side critical section
- *
- * Returns zero if there are no running readers.  Returns a positive
- * number if there is at least one reader within its RCU read-side
- * critical section.  Returns a negative number if an outermost reader
- * is in the midst of exiting from its RCU read-side critical section.
- */
-static int rcu_preempt_running_reader(void)
-{
-	return current->rcu_read_lock_nesting;
-}
-
-/*
- * Check for preempted RCU readers blocking any grace period.
- * If the caller needs a reliable answer, it must disable hard irqs.
- */
-static int rcu_preempt_blocked_readers_any(void)
-{
-	return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
-}
-
-/*
- * Check for preempted RCU readers blocking the current grace period.
- * If the caller needs a reliable answer, it must disable hard irqs.
- */
-static int rcu_preempt_blocked_readers_cgp(void)
-{
-	return rcu_preempt_ctrlblk.gp_tasks != NULL;
-}
-
-/*
- * Return true if another preemptible-RCU grace period is needed.
- */
-static int rcu_preempt_needs_another_gp(void)
-{
-	return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
-}
-
-/*
- * Return true if a preemptible-RCU grace period is in progress.
- * The caller must disable hardirqs.
- */
-static int rcu_preempt_gp_in_progress(void)
-{
-	return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
-}
-
-/*
- * Advance a ->blkd_tasks-list pointer to the next entry, instead
- * returning NULL if at the end of the list.
- */
-static struct list_head *rcu_next_node_entry(struct task_struct *t)
-{
-	struct list_head *np;
-
-	np = t->rcu_node_entry.next;
-	if (np == &rcu_preempt_ctrlblk.blkd_tasks)
-		np = NULL;
-	return np;
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-#ifdef CONFIG_RCU_BOOST
-static void rcu_initiate_boost_trace(void);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Dump additional statistice for TINY_PREEMPT_RCU.
- */
-static void show_tiny_preempt_stats(struct seq_file *m)
-{
-	seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
-		   rcu_preempt_ctrlblk.rcb.qlen,
-		   rcu_preempt_ctrlblk.n_grace_periods,
-		   rcu_preempt_ctrlblk.gpnum,
-		   rcu_preempt_ctrlblk.gpcpu,
-		   rcu_preempt_ctrlblk.completed,
-		   "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
-		   "N."[!rcu_preempt_ctrlblk.gp_tasks],
-		   "E."[!rcu_preempt_ctrlblk.exp_tasks]);
-#ifdef CONFIG_RCU_BOOST
-	seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
-		   "             ",
-		   "B."[!rcu_preempt_ctrlblk.boost_tasks],
-		   rcu_preempt_ctrlblk.n_tasks_boosted,
-		   rcu_preempt_ctrlblk.n_exp_boosts,
-		   rcu_preempt_ctrlblk.n_normal_boosts,
-		   (int)(jiffies & 0xffff),
-		   (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
-	seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
-		   "             balk",
-		   rcu_preempt_ctrlblk.n_balk_blkd_tasks,
-		   rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
-		   rcu_preempt_ctrlblk.n_balk_boost_tasks,
-		   rcu_preempt_ctrlblk.n_balk_notyet,
-		   rcu_preempt_ctrlblk.n_balk_nos);
-#endif /* #ifdef CONFIG_RCU_BOOST */
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-#ifdef CONFIG_RCU_BOOST
-
-#include "rtmutex_common.h"
-
-#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
-
-/* Controls for rcu_kthread() kthread. */
-static struct task_struct *rcu_kthread_task;
-static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
-static unsigned long have_rcu_kthread_work;
-
-/*
- * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
- * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
- */
-static int rcu_boost(void)
-{
-	unsigned long flags;
-	struct rt_mutex mtx;
-	struct task_struct *t;
-	struct list_head *tb;
-
-	if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
-	    rcu_preempt_ctrlblk.exp_tasks == NULL)
-		return 0;  /* Nothing to boost. */
-
-	local_irq_save(flags);
-
-	/*
-	 * Recheck with irqs disabled: all tasks in need of boosting
-	 * might exit their RCU read-side critical sections on their own
-	 * if we are preempted just before disabling irqs.
-	 */
-	if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
-	    rcu_preempt_ctrlblk.exp_tasks == NULL) {
-		local_irq_restore(flags);
-		return 0;
-	}
-
-	/*
-	 * Preferentially boost tasks blocking expedited grace periods.
-	 * This cannot starve the normal grace periods because a second
-	 * expedited grace period must boost all blocked tasks, including
-	 * those blocking the pre-existing normal grace period.
-	 */
-	if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
-		tb = rcu_preempt_ctrlblk.exp_tasks;
-		RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
-	} else {
-		tb = rcu_preempt_ctrlblk.boost_tasks;
-		RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
-	}
-	RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
-
-	/*
-	 * We boost task t by manufacturing an rt_mutex that appears to
-	 * be held by task t.  We leave a pointer to that rt_mutex where
-	 * task t can find it, and task t will release the mutex when it
-	 * exits its outermost RCU read-side critical section.  Then
-	 * simply acquiring this artificial rt_mutex will boost task
-	 * t's priority.  (Thanks to tglx for suggesting this approach!)
-	 */
-	t = container_of(tb, struct task_struct, rcu_node_entry);
-	rt_mutex_init_proxy_locked(&mtx, t);
-	t->rcu_boost_mutex = &mtx;
-	local_irq_restore(flags);
-	rt_mutex_lock(&mtx);
-	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
-
-	return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL ||
-	       ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL;
-}
-
-/*
- * Check to see if it is now time to start boosting RCU readers blocking
- * the current grace period, and, if so, tell the rcu_kthread_task to
- * start boosting them.  If there is an expedited boost in progress,
- * we wait for it to complete.
- *
- * If there are no blocked readers blocking the current grace period,
- * return 0 to let the caller know, otherwise return 1.  Note that this
- * return value is independent of whether or not boosting was done.
- */
-static int rcu_initiate_boost(void)
-{
-	if (!rcu_preempt_blocked_readers_cgp() &&
-	    rcu_preempt_ctrlblk.exp_tasks == NULL) {
-		RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
-		return 0;
-	}
-	if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
-	    (rcu_preempt_ctrlblk.gp_tasks != NULL &&
-	     rcu_preempt_ctrlblk.boost_tasks == NULL &&
-	     ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
-		if (rcu_preempt_ctrlblk.exp_tasks == NULL)
-			rcu_preempt_ctrlblk.boost_tasks =
-				rcu_preempt_ctrlblk.gp_tasks;
-		invoke_rcu_callbacks();
-	} else {
-		RCU_TRACE(rcu_initiate_boost_trace());
-	}
-	return 1;
-}
-
-#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
-
-/*
- * Do priority-boost accounting for the start of a new grace period.
- */
-static void rcu_preempt_boost_start_gp(void)
-{
-	rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
-}
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * If there is no RCU priority boosting, we don't initiate boosting,
- * but we do indicate whether there are blocked readers blocking the
- * current grace period.
- */
-static int rcu_initiate_boost(void)
-{
-	return rcu_preempt_blocked_readers_cgp();
-}
-
-/*
- * If there is no RCU priority boosting, nothing to do at grace-period start.
- */
-static void rcu_preempt_boost_start_gp(void)
-{
-}
-
-#endif /* else #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Record a preemptible-RCU quiescent state for the specified CPU.  Note
- * that this just means that the task currently running on the CPU is
- * in a quiescent state.  There might be any number of tasks blocked
- * while in an RCU read-side critical section.
- *
- * Unlike the other rcu_*_qs() functions, callers to this function
- * must disable irqs in order to protect the assignment to
- * ->rcu_read_unlock_special.
- *
- * Because this is a single-CPU implementation, the only way a grace
- * period can end is if the CPU is in a quiescent state.  The reason is
- * that a blocked preemptible-RCU reader can exit its critical section
- * only if the CPU is running it at the time.  Therefore, when the
- * last task blocking the current grace period exits its RCU read-side
- * critical section, neither the CPU nor blocked tasks will be stopping
- * the current grace period.  (In contrast, SMP implementations
- * might have CPUs running in RCU read-side critical sections that
- * block later grace periods -- but this is not possible given only
- * one CPU.)
- */
-static void rcu_preempt_cpu_qs(void)
-{
-	/* Record both CPU and task as having responded to current GP. */
-	rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
-	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
-
-	/* If there is no GP then there is nothing more to do.  */
-	if (!rcu_preempt_gp_in_progress())
-		return;
-	/*
-	 * Check up on boosting.  If there are readers blocking the
-	 * current grace period, leave.
-	 */
-	if (rcu_initiate_boost())
-		return;
-
-	/* Advance callbacks. */
-	rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
-	rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
-	rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
-
-	/* If there are no blocked readers, next GP is done instantly. */
-	if (!rcu_preempt_blocked_readers_any())
-		rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
-
-	/* If there are done callbacks, cause them to be invoked. */
-	if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
-		invoke_rcu_callbacks();
-}
-
-/*
- * Start a new RCU grace period if warranted.  Hard irqs must be disabled.
- */
-static void rcu_preempt_start_gp(void)
-{
-	if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
-
-		/* Official start of GP. */
-		rcu_preempt_ctrlblk.gpnum++;
-		RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
-		reset_cpu_stall_ticks(&rcu_preempt_ctrlblk.rcb);
-
-		/* Any blocked RCU readers block new GP. */
-		if (rcu_preempt_blocked_readers_any())
-			rcu_preempt_ctrlblk.gp_tasks =
-				rcu_preempt_ctrlblk.blkd_tasks.next;
-
-		/* Set up for RCU priority boosting. */
-		rcu_preempt_boost_start_gp();
-
-		/* If there is no running reader, CPU is done with GP. */
-		if (!rcu_preempt_running_reader())
-			rcu_preempt_cpu_qs();
-	}
-}
-
-/*
- * We have entered the scheduler, and the current task might soon be
- * context-switched away from.  If this task is in an RCU read-side
- * critical section, we will no longer be able to rely on the CPU to
- * record that fact, so we enqueue the task on the blkd_tasks list.
- * If the task started after the current grace period began, as recorded
- * by ->gpcpu, we enqueue at the beginning of the list.  Otherwise
- * before the element referenced by ->gp_tasks (or at the tail if
- * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
- * The task will dequeue itself when it exits the outermost enclosing
- * RCU read-side critical section.  Therefore, the current grace period
- * cannot be permitted to complete until the ->gp_tasks pointer becomes
- * NULL.
- *
- * Caller must disable preemption.
- */
-void rcu_preempt_note_context_switch(void)
-{
-	struct task_struct *t = current;
-	unsigned long flags;
-
-	local_irq_save(flags); /* must exclude scheduler_tick(). */
-	if (rcu_preempt_running_reader() > 0 &&
-	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
-
-		/* Possibly blocking in an RCU read-side critical section. */
-		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
-
-		/*
-		 * If this CPU has already checked in, then this task
-		 * will hold up the next grace period rather than the
-		 * current grace period.  Queue the task accordingly.
-		 * If the task is queued for the current grace period
-		 * (i.e., this CPU has not yet passed through a quiescent
-		 * state for the current grace period), then as long
-		 * as that task remains queued, the current grace period
-		 * cannot end.
-		 */
-		list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
-		if (rcu_cpu_blocking_cur_gp())
-			rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
-	} else if (rcu_preempt_running_reader() < 0 &&
-		   t->rcu_read_unlock_special) {
-		/*
-		 * Complete exit from RCU read-side critical section on
-		 * behalf of preempted instance of __rcu_read_unlock().
-		 */
-		rcu_read_unlock_special(t);
-	}
-
-	/*
-	 * Either we were not in an RCU read-side critical section to
-	 * begin with, or we have now recorded that critical section
-	 * globally.  Either way, we can now note a quiescent state
-	 * for this CPU.  Again, if we were in an RCU read-side critical
-	 * section, and if that critical section was blocking the current
-	 * grace period, then the fact that the task has been enqueued
-	 * means that current grace period continues to be blocked.
-	 */
-	rcu_preempt_cpu_qs();
-	local_irq_restore(flags);
-}
-
-/*
- * Handle special cases during rcu_read_unlock(), such as needing to
- * notify RCU core processing or task having blocked during the RCU
- * read-side critical section.
- */
-void rcu_read_unlock_special(struct task_struct *t)
-{
-	int empty;
-	int empty_exp;
-	unsigned long flags;
-	struct list_head *np;
-#ifdef CONFIG_RCU_BOOST
-	struct rt_mutex *rbmp = NULL;
-#endif /* #ifdef CONFIG_RCU_BOOST */
-	int special;
-
-	/*
-	 * NMI handlers cannot block and cannot safely manipulate state.
-	 * They therefore cannot possibly be special, so just leave.
-	 */
-	if (in_nmi())
-		return;
-
-	local_irq_save(flags);
-
-	/*
-	 * If RCU core is waiting for this CPU to exit critical section,
-	 * let it know that we have done so.
-	 */
-	special = t->rcu_read_unlock_special;
-	if (special & RCU_READ_UNLOCK_NEED_QS)
-		rcu_preempt_cpu_qs();
-
-	/* Hardware IRQ handlers cannot block. */
-	if (in_irq() || in_serving_softirq()) {
-		local_irq_restore(flags);
-		return;
-	}
-
-	/* Clean up if blocked during RCU read-side critical section. */
-	if (special & RCU_READ_UNLOCK_BLOCKED) {
-		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
-
-		/*
-		 * Remove this task from the ->blkd_tasks list and adjust
-		 * any pointers that might have been referencing it.
-		 */
-		empty = !rcu_preempt_blocked_readers_cgp();
-		empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
-		np = rcu_next_node_entry(t);
-		list_del_init(&t->rcu_node_entry);
-		if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
-			rcu_preempt_ctrlblk.gp_tasks = np;
-		if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
-			rcu_preempt_ctrlblk.exp_tasks = np;
-#ifdef CONFIG_RCU_BOOST
-		if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
-			rcu_preempt_ctrlblk.boost_tasks = np;
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
-		/*
-		 * If this was the last task on the current list, and if
-		 * we aren't waiting on the CPU, report the quiescent state
-		 * and start a new grace period if needed.
-		 */
-		if (!empty && !rcu_preempt_blocked_readers_cgp()) {
-			rcu_preempt_cpu_qs();
-			rcu_preempt_start_gp();
-		}
-
-		/*
-		 * If this was the last task on the expedited lists,
-		 * then we need wake up the waiting task.
-		 */
-		if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
-			rcu_report_exp_done();
-	}
-#ifdef CONFIG_RCU_BOOST
-	/* Unboost self if was boosted. */
-	if (t->rcu_boost_mutex != NULL) {
-		rbmp = t->rcu_boost_mutex;
-		t->rcu_boost_mutex = NULL;
-		rt_mutex_unlock(rbmp);
-	}
-#endif /* #ifdef CONFIG_RCU_BOOST */
-	local_irq_restore(flags);
-}
-
-/*
- * Check for a quiescent state from the current CPU.  When a task blocks,
- * the task is recorded in the rcu_preempt_ctrlblk structure, which is
- * checked elsewhere.  This is called from the scheduling-clock interrupt.
- *
- * Caller must disable hard irqs.
- */
-static void rcu_preempt_check_callbacks(void)
-{
-	struct task_struct *t = current;
-
-	if (rcu_preempt_gp_in_progress() &&
-	    (!rcu_preempt_running_reader() ||
-	     !rcu_cpu_blocking_cur_gp()))
-		rcu_preempt_cpu_qs();
-	if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
-	    rcu_preempt_ctrlblk.rcb.donetail)
-		invoke_rcu_callbacks();
-	if (rcu_preempt_gp_in_progress() &&
-	    rcu_cpu_blocking_cur_gp() &&
-	    rcu_preempt_running_reader() > 0)
-		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
-}
-
-/*
- * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
- * update, so this is invoked from rcu_process_callbacks() to
- * handle that case.  Of course, it is invoked for all flavors of
- * RCU, but RCU callbacks can appear only on one of the lists, and
- * neither ->nexttail nor ->donetail can possibly be NULL, so there
- * is no need for an explicit check.
- */
-static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
-{
-	if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
-		rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
-}
-
-/*
- * Process callbacks for preemptible RCU.
- */
-static void rcu_preempt_process_callbacks(void)
-{
-	__rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
-}
-
-/*
- * Queue a preemptible -RCU callback for invocation after a grace period.
- */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
-	unsigned long flags;
-
-	debug_rcu_head_queue(head);
-	head->func = func;
-	head->next = NULL;
-
-	local_irq_save(flags);
-	*rcu_preempt_ctrlblk.nexttail = head;
-	rcu_preempt_ctrlblk.nexttail = &head->next;
-	RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
-	rcu_preempt_start_gp();  /* checks to see if GP needed. */
-	local_irq_restore(flags);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
-/*
- * synchronize_rcu - wait until a grace period has elapsed.
- *
- * Control will return to the caller some time after a full grace
- * period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed.  RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
- */
-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");
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	if (!rcu_scheduler_active)
-		return;
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-	WARN_ON_ONCE(rcu_preempt_running_reader());
-	if (!rcu_preempt_blocked_readers_any())
-		return;
-
-	/* Once we get past the fastpath checks, same code as rcu_barrier(). */
-	if (rcu_expedited)
-		synchronize_rcu_expedited();
-	else
-		rcu_barrier();
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu);
-
-static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
-static unsigned long sync_rcu_preempt_exp_count;
-static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
-
-/*
- * Return non-zero if there are any tasks in RCU read-side critical
- * sections blocking the current preemptible-RCU expedited grace period.
- * If there is no preemptible-RCU expedited grace period currently in
- * progress, returns zero unconditionally.
- */
-static int rcu_preempted_readers_exp(void)
-{
-	return rcu_preempt_ctrlblk.exp_tasks != NULL;
-}
-
-/*
- * 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.
- */
-static void rcu_report_exp_done(void)
-{
-	wake_up(&sync_rcu_preempt_exp_wq);
-}
-
-/*
- * Wait for an rcu-preempt grace period, but expedite it.  The basic idea
- * is to rely in the fact that there is but one CPU, and that it is
- * illegal for a task to invoke synchronize_rcu_expedited() while in a
- * preemptible-RCU read-side critical section.  Therefore, any such
- * critical sections must correspond to blocked tasks, which must therefore
- * be on the ->blkd_tasks list.  So just record the current head of the
- * list in the ->exp_tasks pointer, and wait for all tasks including and
- * after the task pointed to by ->exp_tasks to drain.
- */
-void synchronize_rcu_expedited(void)
-{
-	unsigned long flags;
-	struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
-	unsigned long snap;
-
-	barrier(); /* ensure prior action seen before grace period. */
-
-	WARN_ON_ONCE(rcu_preempt_running_reader());
-
-	/*
-	 * Acquire lock so that there is only one preemptible RCU grace
-	 * period in flight.  Of course, if someone does the expedited
-	 * grace period for us while we are acquiring the lock, just leave.
-	 */
-	snap = sync_rcu_preempt_exp_count + 1;
-	mutex_lock(&sync_rcu_preempt_exp_mutex);
-	if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
-		goto unlock_mb_ret; /* Others did our work for us. */
-
-	local_irq_save(flags);
-
-	/*
-	 * All RCU readers have to already be on blkd_tasks because
-	 * we cannot legally be executing in an RCU read-side critical
-	 * section.
-	 */
-
-	/* Snapshot current head of ->blkd_tasks list. */
-	rpcp->exp_tasks = rpcp->blkd_tasks.next;
-	if (rpcp->exp_tasks == &rpcp->blkd_tasks)
-		rpcp->exp_tasks = NULL;
-
-	/* Wait for tail of ->blkd_tasks list to drain. */
-	if (!rcu_preempted_readers_exp()) {
-		local_irq_restore(flags);
-	} else {
-		rcu_initiate_boost();
-		local_irq_restore(flags);
-		wait_event(sync_rcu_preempt_exp_wq,
-			   !rcu_preempted_readers_exp());
-	}
-
-	/* Clean up and exit. */
-	barrier(); /* ensure expedited GP seen before counter increment. */
-	sync_rcu_preempt_exp_count++;
-unlock_mb_ret:
-	mutex_unlock(&sync_rcu_preempt_exp_mutex);
-	barrier(); /* ensure subsequent action seen after grace period. */
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
-/*
- * Does preemptible RCU need the CPU to stay out of dynticks mode?
- */
-int rcu_preempt_needs_cpu(void)
-{
-	return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
-}
-
-#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
-
 #ifdef CONFIG_RCU_TRACE
 
 /*
@@ -895,79 +138,6 @@ static void rcu_preempt_process_callbacks(void)
 {
 }
 
-#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
-
-#ifdef CONFIG_RCU_BOOST
-
-/*
- * Wake up rcu_kthread() to process callbacks now eligible for invocation
- * or to boost readers.
- */
-static void invoke_rcu_callbacks(void)
-{
-	have_rcu_kthread_work = 1;
-	if (rcu_kthread_task != NULL)
-		wake_up(&rcu_kthread_wq);
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * Is the current CPU running the RCU-callbacks kthread?
- * Caller must have preemption disabled.
- */
-static bool rcu_is_callbacks_kthread(void)
-{
-	return rcu_kthread_task == current;
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-/*
- * This kthread invokes RCU callbacks whose grace periods have
- * elapsed.  It is awakened as needed, and takes the place of the
- * RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
- * This is a kthread, but it is never stopped, at least not until
- * the system goes down.
- */
-static int rcu_kthread(void *arg)
-{
-	unsigned long work;
-	unsigned long morework;
-	unsigned long flags;
-
-	for (;;) {
-		wait_event_interruptible(rcu_kthread_wq,
-					 have_rcu_kthread_work != 0);
-		morework = rcu_boost();
-		local_irq_save(flags);
-		work = have_rcu_kthread_work;
-		have_rcu_kthread_work = morework;
-		local_irq_restore(flags);
-		if (work)
-			rcu_process_callbacks(NULL);
-		schedule_timeout_interruptible(1); /* Leave CPU for others. */
-	}
-
-	return 0;  /* Not reached, but needed to shut gcc up. */
-}
-
-/*
- * Spawn the kthread that invokes RCU callbacks.
- */
-static int __init rcu_spawn_kthreads(void)
-{
-	struct sched_param sp;
-
-	rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
-	sp.sched_priority = RCU_BOOST_PRIO;
-	sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
-	return 0;
-}
-early_initcall(rcu_spawn_kthreads);
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
 /* Hold off callback invocation until early_initcall() time. */
 static int rcu_scheduler_fully_active __read_mostly;
 
@@ -1001,8 +171,6 @@ static int __init rcu_scheduler_really_started(void)
 }
 early_initcall(rcu_scheduler_really_started);
 
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
-
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 #include <linux/kernel_stat.h>
 
@@ -1020,25 +188,6 @@ void __init rcu_scheduler_starting(void)
 
 #ifdef CONFIG_RCU_TRACE
 
-#ifdef CONFIG_RCU_BOOST
-
-static void rcu_initiate_boost_trace(void)
-{
-	if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
-		rcu_preempt_ctrlblk.n_balk_blkd_tasks++;
-	else if (rcu_preempt_ctrlblk.gp_tasks == NULL &&
-		 rcu_preempt_ctrlblk.exp_tasks == NULL)
-		rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++;
-	else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
-		rcu_preempt_ctrlblk.n_balk_boost_tasks++;
-	else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
-		rcu_preempt_ctrlblk.n_balk_notyet++;
-	else
-		rcu_preempt_ctrlblk.n_balk_nos++;
-}
-
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
 static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
 {
 	unsigned long flags;
@@ -1105,9 +254,6 @@ MODULE_LICENSE("GPL");
 
 static void check_cpu_stall_preempt(void)
 {
-#ifdef CONFIG_TINY_PREEMPT_RCU
-	check_cpu_stall(&rcu_preempt_ctrlblk.rcb);
-#endif /* #ifdef CONFIG_TINY_PREEMPT_RCU */
 }
 
 #endif /* #ifdef CONFIG_RCU_TRACE */
-- 
1.8.1.5

[PATCH tip/core/rcu 02/12] rcu: Remove show_tiny_preempt_stats()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

With the removal of CONFIG_TINY_PREEMPT_RCU, show_tiny_preempt_stats()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny_plugin.h | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 29a4dd7..cf0bc22 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -102,18 +102,6 @@ static void check_cpu_stalls(void)
 	RCU_TRACE(check_cpu_stall_preempt());
 }
 
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * Because preemptible RCU does not exist, it is not necessary to
- * dump out its statistics.
- */
-static void show_tiny_preempt_stats(struct seq_file *m)
-{
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
 /*
  * Because preemptible RCU does not exist, it never has any callbacks
  * to check.
@@ -202,7 +190,6 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
  */
 static int show_tiny_stats(struct seq_file *m, void *unused)
 {
-	show_tiny_preempt_stats(m);
 	seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
 	seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
 	return 0;
-- 
1.8.1.5

[PATCH tip/core/rcu 03/12] rcu: Remove rcu_preempt_check_callbacks()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_check_callbacks()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny.c        | 1 -
 kernel/rcutiny_plugin.h | 8 --------
 2 files changed, 9 deletions(-)

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index a0714a5..9178282 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -257,7 +257,6 @@ void rcu_check_callbacks(int cpu, int user)
 		rcu_sched_qs(cpu);
 	else if (!in_softirq())
 		rcu_bh_qs(cpu);
-	rcu_preempt_check_callbacks();
 }
 
 /*
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index cf0bc22..404b3a3 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -104,14 +104,6 @@ static void check_cpu_stalls(void)
 
 /*
  * Because preemptible RCU does not exist, it never has any callbacks
- * to check.
- */
-static void rcu_preempt_check_callbacks(void)
-{
-}
-
-/*
- * Because preemptible RCU does not exist, it never has any callbacks
  * to remove.
  */
 static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
-- 
1.8.1.5

[PATCH tip/core/rcu 04/12] rcu: Remove rcu_preempt_remove_callbacks()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_remove_callbacks()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny.c        | 1 -
 kernel/rcutiny_plugin.h | 8 --------
 2 files changed, 9 deletions(-)

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 9178282..6f5a2a6 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -289,7 +289,6 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	*rcp->donetail = NULL;
 	if (rcp->curtail == rcp->donetail)
 		rcp->curtail = &rcp->rcucblist;
-	rcu_preempt_remove_callbacks(rcp);
 	rcp->donetail = &rcp->rcucblist;
 	local_irq_restore(flags);
 
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 404b3a3..8b835b9 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -104,14 +104,6 @@ static void check_cpu_stalls(void)
 
 /*
  * Because preemptible RCU does not exist, it never has any callbacks
- * to remove.
- */
-static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
-{
-}
-
-/*
- * Because preemptible RCU does not exist, it never has any callbacks
  * to process.
  */
 static void rcu_preempt_process_callbacks(void)
-- 
1.8.1.5

[PATCH tip/core/rcu 05/12] rcu: Remove rcu_preempt_process_callbacks()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_process_callbacks()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny.c        | 1 -
 kernel/rcutiny_plugin.h | 8 --------
 2 files changed, 9 deletions(-)

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 6f5a2a6..7fc2339 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -314,7 +314,6 @@ static void rcu_process_callbacks(struct softirq_action *unused)
 {
 	__rcu_process_callbacks(&rcu_sched_ctrlblk);
 	__rcu_process_callbacks(&rcu_bh_ctrlblk);
-	rcu_preempt_process_callbacks();
 }
 
 /*
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 8b835b9..bfe9924 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -102,14 +102,6 @@ static void check_cpu_stalls(void)
 	RCU_TRACE(check_cpu_stall_preempt());
 }
 
-/*
- * Because preemptible RCU does not exist, it never has any callbacks
- * to process.
- */
-static void rcu_preempt_process_callbacks(void)
-{
-}
-
 /* Hold off callback invocation until early_initcall() time. */
 static int rcu_scheduler_fully_active __read_mostly;
 
-- 
1.8.1.5

[PATCH tip/core/rcu 06/12] rcu: Simplify RCU_TINY RCU callback invocation

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

TINY_PREEMPT_RCU could use a kthread to handle RCU callback invocation,
which required an API to abstract kthread vs. softirq invocation.
Now that TINY_PREEMPT_RCU is no longer with us, this commit retires
this API in favor of direct use of the relevant softirq primitives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h |  1 +
 include/linux/rcutiny.h  |  4 ----
 include/linux/rcutree.h  |  1 -
 kernel/rcutiny.c         | 14 +++++++++-----
 kernel/rcutiny_plugin.h  | 33 ---------------------------------
 5 files changed, 10 insertions(+), 43 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0a8276d..1c53a9f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -216,6 +216,7 @@ static inline int rcu_preempt_depth(void)
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 /* Internal to kernel */
+extern void rcu_init(void);
 extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
 extern void rcu_check_callbacks(int cpu, int user);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4e56a9c..592fad8 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,10 +27,6 @@
 
 #include <linux/cache.h>
 
-static inline void rcu_init(void)
-{
-}
-
 static inline void rcu_barrier_bh(void)
 {
 	wait_rcu_gp(call_rcu_bh);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 952b793..3f1aa8f 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -30,7 +30,6 @@
 #ifndef __LINUX_RCUTREE_H
 #define __LINUX_RCUTREE_H
 
-extern void rcu_init(void);
 extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies);
 extern void rcu_cpu_stall_reset(void);
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 7fc2339..4adc9e2 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -44,7 +44,6 @@
 
 /* Forward declarations for rcutiny_plugin.h. */
 struct rcu_ctrlblk;
-static void invoke_rcu_callbacks(void);
 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
 static void rcu_process_callbacks(struct softirq_action *unused);
 static void __call_rcu(struct rcu_head *head,
@@ -227,7 +226,7 @@ void rcu_sched_qs(int cpu)
 	local_irq_save(flags);
 	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 	    rcu_qsctr_help(&rcu_bh_ctrlblk))
-		invoke_rcu_callbacks();
+		raise_softirq(RCU_SOFTIRQ);
 	local_irq_restore(flags);
 }
 
@@ -240,7 +239,7 @@ void rcu_bh_qs(int cpu)
 
 	local_irq_save(flags);
 	if (rcu_qsctr_help(&rcu_bh_ctrlblk))
-		invoke_rcu_callbacks();
+		raise_softirq(RCU_SOFTIRQ);
 	local_irq_restore(flags);
 }
 
@@ -277,7 +276,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 					      ACCESS_ONCE(rcp->rcucblist),
 					      need_resched(),
 					      is_idle_task(current),
-					      rcu_is_callbacks_kthread()));
+					      false));
 		return;
 	}
 
@@ -307,7 +306,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 	RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
 				      is_idle_task(current),
-				      rcu_is_callbacks_kthread()));
+				      false));
 }
 
 static void rcu_process_callbacks(struct softirq_action *unused)
@@ -379,3 +378,8 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 	__call_rcu(head, func, &rcu_bh_ctrlblk);
 }
 EXPORT_SYMBOL_GPL(call_rcu_bh);
+
+void rcu_init(void)
+{
+	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+}
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index bfe9924..36fd83c 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -102,39 +102,6 @@ static void check_cpu_stalls(void)
 	RCU_TRACE(check_cpu_stall_preempt());
 }
 
-/* Hold off callback invocation until early_initcall() time. */
-static int rcu_scheduler_fully_active __read_mostly;
-
-/*
- * Start up softirq processing of callbacks.
- */
-void invoke_rcu_callbacks(void)
-{
-	if (rcu_scheduler_fully_active)
-		raise_softirq(RCU_SOFTIRQ);
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * There is no callback kthread, so this thread is never it.
- */
-static bool rcu_is_callbacks_kthread(void)
-{
-	return false;
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-static int __init rcu_scheduler_really_started(void)
-{
-	rcu_scheduler_fully_active = 1;
-	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
-	raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
-	return 0;
-}
-early_initcall(rcu_scheduler_really_started);
-
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 #include <linux/kernel_stat.h>
 
-- 
1.8.1.5

[PATCH tip/core/rcu 07/12] rcu: Remove check_cpu_stall_preempt()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

With the removal of CONFIG_TINY_PREEMPT_RCU, check_cpu_stall_preempt()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny_plugin.h | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 36fd83c..bac3a6e 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -82,8 +82,6 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 		rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
 }
 
-static void check_cpu_stall_preempt(void);
-
 #endif /* #ifdef CONFIG_RCU_TRACE */
 
 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
@@ -99,7 +97,6 @@ static void check_cpu_stalls(void)
 {
 	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
 	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
-	RCU_TRACE(check_cpu_stall_preempt());
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -182,8 +179,4 @@ MODULE_AUTHOR("Paul E. McKenney");
 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
 MODULE_LICENSE("GPL");
 
-static void check_cpu_stall_preempt(void)
-{
-}
-
 #endif /* #ifdef CONFIG_RCU_TRACE */
-- 
1.8.1.5

[PATCH tip/core/rcu 08/12] rcu: Remove the CONFIG_TINY_RCU ifdefs in rcutiny.h

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Now that CONFIG_TINY_PREEMPT_RCU is no more, this commit removes
the CONFIG_TINY_RCU ifdefs from include/linux/rcutiny.h in favor of
unconditionally compiling the CONFIG_TINY_RCU legs of those ifdefs.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h | 28 ----------------------------
 1 file changed, 28 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 592fad8..07b5aff 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -37,8 +37,6 @@ static inline void rcu_barrier_sched(void)
 	wait_rcu_gp(call_rcu_sched);
 }
 
-#ifdef CONFIG_TINY_RCU
-
 static inline void synchronize_rcu_expedited(void)
 {
 	synchronize_sched();	/* Only one CPU, so pretty fast anyway!!! */
@@ -49,17 +47,6 @@ static inline void rcu_barrier(void)
 	rcu_barrier_sched();  /* Only one CPU, so only one list of callbacks! */
 }
 
-#else /* #ifdef CONFIG_TINY_RCU */
-
-void synchronize_rcu_expedited(void);
-
-static inline void rcu_barrier(void)
-{
-	wait_rcu_gp(call_rcu);
-}
-
-#endif /* #else #ifdef CONFIG_TINY_RCU */
-
 static inline void synchronize_rcu_bh(void)
 {
 	synchronize_sched();
@@ -81,8 +68,6 @@ static inline void kfree_call_rcu(struct rcu_head *head,
 	call_rcu(head, func);
 }
 
-#ifdef CONFIG_TINY_RCU
-
 static inline void rcu_preempt_note_context_switch(void)
 {
 }
@@ -93,19 +78,6 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
 	return 0;
 }
 
-#else /* #ifdef CONFIG_TINY_RCU */
-
-void rcu_preempt_note_context_switch(void);
-int rcu_preempt_needs_cpu(void);
-
-static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
-{
-	*delta_jiffies = ULONG_MAX;
-	return rcu_preempt_needs_cpu();
-}
-
-#endif /* #else #ifdef CONFIG_TINY_RCU */
-
 static inline void rcu_note_context_switch(int cpu)
 {
 	rcu_sched_qs(cpu);
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 08/12] rcu: Remove the CONFIG_TINY_RCU ifdefs in rcutiny.h

[Josh Triplett]

On Fri, Apr 12, 2013 at 04:48:27PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> Now that CONFIG_TINY_PREEMPT_RCU is no more, this commit removes
> the CONFIG_TINY_RCU ifdefs from include/linux/rcutiny.h in favor of
> unconditionally compiling the CONFIG_TINY_RCU legs of those ifdefs.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

The #else branches of these ifdefs ought to disappear in the first patch
of the series, since they cover the CONFIG_TINY_PREEMPT_RCU case.

- Josh Triplett

[PATCH tip/core/rcu 09/12] rcu: Remove rcu_preempt_note_context_switch()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_note_context_switch()
is now an empty function.  This commit therefore eliminates it by inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcutiny.h | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 07b5aff..51230b6 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -68,10 +68,6 @@ static inline void kfree_call_rcu(struct rcu_head *head,
 	call_rcu(head, func);
 }
 
-static inline void rcu_preempt_note_context_switch(void)
-{
-}
-
 static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
 {
 	*delta_jiffies = ULONG_MAX;
@@ -81,7 +77,6 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
 static inline void rcu_note_context_switch(int cpu)
 {
 	rcu_sched_qs(cpu);
-	rcu_preempt_note_context_switch();
 }
 
 /*
-- 
1.8.1.5

[PATCH tip/core/rcu 10/12] rcu: Consolidate rcutiny_plugin.h ifdefs

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

This commit rearranges code in order to allow ifdefs to be consolidated
in kernel/rcutiny_plugin.h, simplifying the code.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny_plugin.h | 86 +++++++++++++++++++++++--------------------------
 1 file changed, 40 insertions(+), 46 deletions(-)

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index bac3a6e..65ef180 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -53,54 +53,10 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 };
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
+#include <linux/kernel_stat.h>
+
 int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-#ifdef CONFIG_RCU_TRACE
-
-static void check_cpu_stall(struct rcu_ctrlblk *rcp)
-{
-	unsigned long j;
-	unsigned long js;
-
-	if (rcu_cpu_stall_suppress)
-		return;
-	rcp->ticks_this_gp++;
-	j = jiffies;
-	js = rcp->jiffies_stall;
-	if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
-		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
-		       rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
-		       jiffies - rcp->gp_start, rcp->qlen);
-		dump_stack();
-	}
-	if (*rcp->curtail && ULONG_CMP_GE(j, js))
-		rcp->jiffies_stall = jiffies +
-			3 * rcu_jiffies_till_stall_check() + 3;
-	else if (ULONG_CMP_GE(j, js))
-		rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
-{
-#ifdef CONFIG_RCU_TRACE
-	rcp->ticks_this_gp = 0;
-	rcp->gp_start = jiffies;
-	rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
-#endif /* #ifdef CONFIG_RCU_TRACE */
-}
-
-static void check_cpu_stalls(void)
-{
-	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
-	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
-}
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-#include <linux/kernel_stat.h>
 
 /*
  * During boot, we forgive RCU lockdep issues.  After this function is
@@ -179,4 +135,42 @@ MODULE_AUTHOR("Paul E. McKenney");
 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
 MODULE_LICENSE("GPL");
 
+static void check_cpu_stall(struct rcu_ctrlblk *rcp)
+{
+	unsigned long j;
+	unsigned long js;
+
+	if (rcu_cpu_stall_suppress)
+		return;
+	rcp->ticks_this_gp++;
+	j = jiffies;
+	js = rcp->jiffies_stall;
+	if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
+		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
+		       rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
+		       jiffies - rcp->gp_start, rcp->qlen);
+		dump_stack();
+	}
+	if (*rcp->curtail && ULONG_CMP_GE(j, js))
+		rcp->jiffies_stall = jiffies +
+			3 * rcu_jiffies_till_stall_check() + 3;
+	else if (ULONG_CMP_GE(j, js))
+		rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+}
+
 #endif /* #ifdef CONFIG_RCU_TRACE */
+
+static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
+{
+#ifdef CONFIG_RCU_TRACE
+	rcp->ticks_this_gp = 0;
+	rcp->gp_start = jiffies;
+	rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
+#endif /* #ifdef CONFIG_RCU_TRACE */
+}
+
+static void check_cpu_stalls(void)
+{
+	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
+	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
+}
-- 
1.8.1.5

[PATCH tip/core/rcu 11/12] rcu: Remove TINY_PREEMPT_RCU tracing documentation

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Because TINY_PREEMPT_RCU is no more, this commit removes its tracing
formats from the documentation.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 Documentation/RCU/trace.txt | 100 ++------------------------------------------
 1 file changed, 4 insertions(+), 96 deletions(-)

diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index c776968..f3778f8 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -530,113 +530,21 @@ o	"nos" counts the number of times we balked for other
 	reasons, e.g., the grace period ended first.
 
 
-CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats
+CONFIG_TINY_RCU debugfs Files and Formats
 
 These implementations of RCU provides a single debugfs file under the
 top-level directory RCU, namely rcu/rcudata, which displays fields in
-rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU,
-rcu_preempt_ctrlblk.
+rcu_bh_ctrlblk and rcu_sched_ctrlblk.
 
 The output of "cat rcu/rcudata" is as follows:
 
-rcu_preempt: qlen=24 gp=1097669 g197/p197/c197 tasks=...
-             ttb=. btg=no ntb=184 neb=0 nnb=183 j=01f7 bt=0274
-             normal balk: nt=1097669 gt=0 bt=371 b=0 ny=25073378 nos=0
-             exp balk: bt=0 nos=0
 rcu_sched: qlen: 0
 rcu_bh: qlen: 0
 
-This is split into rcu_preempt, rcu_sched, and rcu_bh sections, with the
-rcu_preempt section appearing only in CONFIG_TINY_PREEMPT_RCU builds.
-The last three lines of the rcu_preempt section appear only in
-CONFIG_RCU_BOOST kernel builds.  The fields are as follows:
+This is split into rcu_sched and rcu_bh sections.  The field is as
+follows:
 
 o	"qlen" is the number of RCU callbacks currently waiting either
 	for an RCU grace period or waiting to be invoked.  This is the
 	only field present for rcu_sched and rcu_bh, due to the
 	short-circuiting of grace period in those two cases.
-
-o	"gp" is the number of grace periods that have completed.
-
-o	"g197/p197/c197" displays the grace-period state, with the
-	"g" number being the number of grace periods that have started
-	(mod 256), the "p" number being the number of grace periods
-	that the CPU has responded to (also mod 256), and the "c"
-	number being the number of grace periods that have completed
-	(once again mode 256).
-
-	Why have both "gp" and "g"?  Because the data flowing into
-	"gp" is only present in a CONFIG_RCU_TRACE kernel.
-
-o	"tasks" is a set of bits.  The first bit is "T" if there are
-	currently tasks that have recently blocked within an RCU
-	read-side critical section, the second bit is "N" if any of the
-	aforementioned tasks are blocking the current RCU grace period,
-	and the third bit is "E" if any of the aforementioned tasks are
-	blocking the current expedited grace period.  Each bit is "."
-	if the corresponding condition does not hold.
-
-o	"ttb" is a single bit.  It is "B" if any of the blocked tasks
-	need to be priority boosted and "." otherwise.
-
-o	"btg" indicates whether boosting has been carried out during
-	the current grace period, with "exp" indicating that boosting
-	is in progress for an expedited grace period, "no" indicating
-	that boosting has not yet started for a normal grace period,
-	"begun" indicating that boosting has bebug for a normal grace
-	period, and "done" indicating that boosting has completed for
-	a normal grace period.
-
-o	"ntb" is the total number of tasks subjected to RCU priority boosting
-	periods since boot.
-
-o	"neb" is the number of expedited grace periods that have had
-	to resort to RCU priority boosting since boot.
-
-o	"nnb" is the number of normal grace periods that have had
-	to resort to RCU priority boosting since boot.
-
-o	"j" is the low-order 16 bits of the jiffies counter in hexadecimal.
-
-o	"bt" is the low-order 16 bits of the value that the jiffies counter
-	will have at the next time that boosting is scheduled to begin.
-
-o	In the line beginning with "normal balk", the fields are as follows:
-
-	o	"nt" is the number of times that the system balked from
-		boosting because there were no blocked tasks to boost.
-		Note that the system will balk from boosting even if the
-		grace period is overdue when the currently running task
-		is looping within an RCU read-side critical section.
-		There is no point in boosting in this case, because
-		boosting a running task won't make it run any faster.
-
-	o	"gt" is the number of times that the system balked
-		from boosting because, although there were blocked tasks,
-		none of them were preventing the current grace period
-		from completing.
-
-	o	"bt" is the number of times that the system balked
-		from boosting because boosting was already in progress.
-
-	o	"b" is the number of times that the system balked from
-		boosting because boosting had already completed for
-		the grace period in question.
-
-	o	"ny" is the number of times that the system balked from
-		boosting because it was not yet time to start boosting
-		the grace period in question.
-
-	o	"nos" is the number of times that the system balked from
-		boosting for inexplicable ("not otherwise specified")
-		reasons.  This can actually happen due to races involving
-		increments of the jiffies counter.
-
-o	In the line beginning with "exp balk", the fields are as follows:
-
-	o	"bt" is the number of times that the system balked from
-		boosting because there were no blocked tasks to boost.
-
-	o	"nos" is the number of times that the system balked from
-		 boosting for inexplicable ("not otherwise specified")
-		 reasons.
-- 
1.8.1.5

[PATCH tip/core/rcu 12/12] rcu: Shrink TINY_RCU by moving exit_rcu()

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Now that TINY_PREEMPT_RCU is no more, exit_rcu() is always an empty
function.  But if TINY_RCU is going to have an empty function, it should
be in include/linux/rcutiny.h, where it does not bloat the kernel.
This commit therefore moves exit_rcu() out of kernel/rcupdate.c to
kernel/rcutree_plugin.h, and places a static inline empty function in
include/linux/rcutiny.h in order to shrink TINY_RCU a bit.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h |  2 --
 include/linux/rcutiny.h  |  4 ++++
 include/linux/rcutree.h  |  2 ++
 kernel/rcupdate.c        | 26 +-------------------------
 kernel/rcutree_plugin.h  | 26 ++++++++++++++++++++++++++
 5 files changed, 33 insertions(+), 27 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 1c53a9f..1d0145a 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -240,8 +240,6 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
 					 struct task_struct *next) { }
 #endif /* CONFIG_RCU_USER_QS */
 
-extern void exit_rcu(void);
-
 /**
  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
  * @a: Code that RCU needs to pay attention to.
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 51230b6..e31005e 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -119,6 +119,10 @@ static inline void rcu_cpu_stall_reset(void)
 {
 }
 
+static inline void exit_rcu(void)
+{
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 extern int rcu_scheduler_active __read_mostly;
 extern void rcu_scheduler_starting(void);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 3f1aa8f..226169d 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -85,6 +85,8 @@ extern void rcu_force_quiescent_state(void);
 extern void rcu_bh_force_quiescent_state(void);
 extern void rcu_sched_force_quiescent_state(void);
 
+extern void exit_rcu(void);
+
 extern void rcu_scheduler_starting(void);
 extern int rcu_scheduler_active __read_mostly;
 
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 48ab703..0be1fa2 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -104,31 +104,7 @@ void __rcu_read_unlock(void)
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 
-/*
- * Check for a task exiting while in a preemptible-RCU read-side
- * critical section, clean up if so.  No need to issue warnings,
- * as debug_check_no_locks_held() already does this if lockdep
- * is enabled.
- */
-void exit_rcu(void)
-{
-	struct task_struct *t = current;
-
-	if (likely(list_empty(&current->rcu_node_entry)))
-		return;
-	t->rcu_read_lock_nesting = 1;
-	barrier();
-	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
-	__rcu_read_unlock();
-}
-
-#else /* #ifdef CONFIG_PREEMPT_RCU */
-
-void exit_rcu(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index e6cf7e5..086daaf 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -931,6 +931,24 @@ static void __init __rcu_init_preempt(void)
 	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
 }
 
+/*
+ * Check for a task exiting while in a preemptible-RCU read-side
+ * critical section, clean up if so.  No need to issue warnings,
+ * as debug_check_no_locks_held() already does this if lockdep
+ * is enabled.
+ */
+void exit_rcu(void)
+{
+	struct task_struct *t = current;
+
+	if (likely(list_empty(&current->rcu_node_entry)))
+		return;
+	t->rcu_read_lock_nesting = 1;
+	barrier();
+	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
+	__rcu_read_unlock();
+}
+
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 static struct rcu_state *rcu_state = &rcu_sched_state;
@@ -1099,6 +1117,14 @@ static void __init __rcu_init_preempt(void)
 {
 }
 
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 #ifdef CONFIG_RCU_BOOST
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 0/12] TINY_RCU changes for 3.11

[Josh Triplett]

On Fri, Apr 12, 2013 at 04:48:10PM -0700, Paul E. McKenney wrote:
> This series removes TINY_PREEMPT_RCU, as promised/threatened at
> http://lwn.net/Articles/541037/ and https://lkml.org/lkml/2012/11/12/545.
> 
> 1.	Remove TINY_PREEMPT_RCU.  This is a straight syntactic removal,
> 	with no attempt at cleanup.  The remaining patches do the cleanup.
> 
> 2.	Inline the now-empty show_tiny_preempt_stats() function.
> 
> 3.	Inline the now-empty rcu_preempt_check_callbacks() function.
> 
> 4.	Inline the now-empty rcu_preempt_remove_callbacks() function.
> 
> 5.	Inline the now-empty rcu_preempt_process_callbacks() function.
> 
> 6.	Because TINY_RCU no longer has kthreads, remove the code that
> 	used to abstract away kthread vs. softirq invocation.
> 
> 7.	Inline the now-empty check_cpu_stall_preempt() function.
> 
> 8.	Remove CONFIG_TINY_RCU ifdefs from include/linux/rcutiny.h
> 
> 9.	Inline the now-empty rcu_preempt_note_context_switch() function.
> 
> 10.	Move code to allow consolidating ifdefs in kernel/rcutiny_plugin.h.
> 
> 11.	Remove TINY_PREEMPT_RCU's tracing formats from documentation.
> 
> 12.	Shrink TINY_RCU a bit by moving exit_rcu() to TREE_RCU, leaving
> 	TINY_RCU with a static inline empty function.

For 2-7 and 9-12:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

I responded to patch 8 with a note about moving part of it to patch 1;
with that changed,
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
for those two as well.

Re: [PATCH tip/core/rcu 0/12] TINY_RCU changes for 3.11

[Paul E. McKenney]

On Sat, Apr 13, 2013 at 11:30:49AM -0700, Josh Triplett wrote:
> On Fri, Apr 12, 2013 at 04:48:10PM -0700, Paul E. McKenney wrote:
> > This series removes TINY_PREEMPT_RCU, as promised/threatened at
> > http://lwn.net/Articles/541037/ and https://lkml.org/lkml/2012/11/12/545.
> > 
> > 1.	Remove TINY_PREEMPT_RCU.  This is a straight syntactic removal,
> > 	with no attempt at cleanup.  The remaining patches do the cleanup.
> > 
> > 2.	Inline the now-empty show_tiny_preempt_stats() function.
> > 
> > 3.	Inline the now-empty rcu_preempt_check_callbacks() function.
> > 
> > 4.	Inline the now-empty rcu_preempt_remove_callbacks() function.
> > 
> > 5.	Inline the now-empty rcu_preempt_process_callbacks() function.
> > 
> > 6.	Because TINY_RCU no longer has kthreads, remove the code that
> > 	used to abstract away kthread vs. softirq invocation.
> > 
> > 7.	Inline the now-empty check_cpu_stall_preempt() function.
> > 
> > 8.	Remove CONFIG_TINY_RCU ifdefs from include/linux/rcutiny.h
> > 
> > 9.	Inline the now-empty rcu_preempt_note_context_switch() function.
> > 
> > 10.	Move code to allow consolidating ifdefs in kernel/rcutiny_plugin.h.
> > 
> > 11.	Remove TINY_PREEMPT_RCU's tracing formats from documentation.
> > 
> > 12.	Shrink TINY_RCU a bit by moving exit_rcu() to TREE_RCU, leaving
> > 	TINY_RCU with a static inline empty function.
> 
> For 2-7 and 9-12:
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> 
> I responded to patch 8 with a note about moving part of it to patch 1;
> with that changed,
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> for those two as well.

Thank you for the review, and good point on merging patch 8 into patch 1,
will do!

							Thanx, Paul