[PATCH tip/core/rcu 0/13] v2 TINY_RCU changes for 3.11

[PATCH tip/core/rcu 0/13] v2 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.

13.	Shrink TINY_RCU a bit more by making reset_cpu_stall_ticks() and
	check_cpu_stalls() inlineable.

Changes from v1: Add Reviewed-bys and add the 13th patch.

							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     |   45 -
 b/include/linux/rcutree.h     |    3 
 b/init/Kconfig                |   10 
 b/kernel/rcupdate.c           |   26 -
 b/kernel/rcutiny.c            |   21 
 b/kernel/rcutiny_plugin.h     | 1023 +-----------------------------------------
 b/kernel/rcutree_plugin.h     |   26 +
 10 files changed, 96 insertions(+), 1165 deletions(-)

[PATCH tip/core/rcu 01/13] 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>
[ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ]
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 include/linux/hardirq.h  |   2 +-
 include/linux/rcupdate.h |   2 +-
 include/linux/rcutiny.h  |  24 +-
 init/Kconfig             |  10 +-
 kernel/rcutiny_plugin.h  | 854 -----------------------------------------------
 5 files changed, 5 insertions(+), 887 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 4ccd68e..b6dc04d 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/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4e56a9c..d3c094f 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -53,16 +53,7 @@ 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 */
+#endif /* #ifdef CONFIG_TINY_RCU */
 
 static inline void synchronize_rcu_bh(void)
 {
@@ -97,18 +88,7 @@ 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 */
+#endif /* #ifdef CONFIG_TINY_RCU */
 
 static inline void rcu_note_context_switch(int cpu)
 {
diff --git a/init/Kconfig b/init/Kconfig
index 9d3a788..a21479e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -458,18 +458,10 @@ 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 02/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 03/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 04/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 05/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 06/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 b6dc04d..cfb02ee 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 d3c094f..e756251 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 07/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 08/13] 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>
[ paulmck: Moved removal of #else to "Remove TINY_PREEMPT_RCU" as
  suggested by Josh Triplett. ]
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 include/linux/rcutiny.h | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index e756251..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!!! */
@@ -49,8 +47,6 @@ static inline void rcu_barrier(void)
 	rcu_barrier_sched();  /* Only one CPU, so only one list of callbacks! */
 }
 
-#endif /* #ifdef CONFIG_TINY_RCU */
-
 static inline void synchronize_rcu_bh(void)
 {
 	synchronize_sched();
@@ -72,8 +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)
 {
 }
@@ -84,8 +78,6 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
 	return 0;
 }
 
-#endif /* #ifdef CONFIG_TINY_RCU */
-
 static inline void rcu_note_context_switch(int cpu)
 {
 	rcu_sched_qs(cpu);
-- 
1.8.1.5

[PATCH tip/core/rcu 09/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 10/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 11/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 12/13] 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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 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 cfb02ee..9275dc2 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 207844e..de701bb 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -932,6 +932,24 @@ 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;
@@ -1100,6 +1118,14 @@ 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

[PATCH tip/core/rcu 13/13] rcu: Shrink TINY_RCU by reworking CPU-stall ifdefs

[Paul E. McKenney]

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

TINY_RCU's reset_cpu_stall_ticks() and check_cpu_stalls() functions
are defined unconditionally, and are empty functions if CONFIG_RCU_TRACE
is disabled (which in turns disables detection of RCU CPU stalls).
These empty functions can add a bit of bloat to TINY_RCU, so this
commit reworks the ifdefs so that these functions are defined only
if they actually do something.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutiny.c        | 4 ++--
 kernel/rcutiny_plugin.h | 6 ++----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 4adc9e2..aa34411 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -204,7 +204,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-	reset_cpu_stall_ticks(rcp);
+	RCU_TRACE(reset_cpu_stall_ticks(rcp));
 	if (rcp->rcucblist != NULL &&
 	    rcp->donetail != rcp->curtail) {
 		rcp->donetail = rcp->curtail;
@@ -251,7 +251,7 @@ void rcu_bh_qs(int cpu)
  */
 void rcu_check_callbacks(int cpu, int user)
 {
-	check_cpu_stalls();
+	RCU_TRACE(check_cpu_stalls());
 	if (user || rcu_is_cpu_rrupt_from_idle())
 		rcu_sched_qs(cpu);
 	else if (!in_softirq())
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 65ef180..0cd385a 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -158,15 +158,11 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 		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)
@@ -174,3 +170,5 @@ static void check_cpu_stalls(void)
 	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
 	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
 }
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 13/13] rcu: Shrink TINY_RCU by reworking CPU-stall ifdefs

[Josh Triplett]

On Mon, May 20, 2013 at 07:58:20AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> TINY_RCU's reset_cpu_stall_ticks() and check_cpu_stalls() functions
> are defined unconditionally, and are empty functions if CONFIG_RCU_TRACE
> is disabled (which in turns disables detection of RCU CPU stalls).
> These empty functions can add a bit of bloat to TINY_RCU, so this
> commit reworks the ifdefs so that these functions are defined only
> if they actually do something.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Strange.  Both of these functions are static, and called in only one
place, so shouldn't the compiler inline them (and thus throw them away
completely when empty)?  Why does it not do so?

- Josh Triplett

> ---
>  kernel/rcutiny.c        | 4 ++--
>  kernel/rcutiny_plugin.h | 6 ++----
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
> index 4adc9e2..aa34411 100644
> --- a/kernel/rcutiny.c
> +++ b/kernel/rcutiny.c
> @@ -204,7 +204,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
>   */
>  static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
>  {
> -	reset_cpu_stall_ticks(rcp);
> +	RCU_TRACE(reset_cpu_stall_ticks(rcp));
>  	if (rcp->rcucblist != NULL &&
>  	    rcp->donetail != rcp->curtail) {
>  		rcp->donetail = rcp->curtail;
> @@ -251,7 +251,7 @@ void rcu_bh_qs(int cpu)
>   */
>  void rcu_check_callbacks(int cpu, int user)
>  {
> -	check_cpu_stalls();
> +	RCU_TRACE(check_cpu_stalls());
>  	if (user || rcu_is_cpu_rrupt_from_idle())
>  		rcu_sched_qs(cpu);
>  	else if (!in_softirq())
> diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
> index 65ef180..0cd385a 100644
> --- a/kernel/rcutiny_plugin.h
> +++ b/kernel/rcutiny_plugin.h
> @@ -158,15 +158,11 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
>  		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)
> @@ -174,3 +170,5 @@ static void check_cpu_stalls(void)
>  	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
>  	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
>  }
> +
> +#endif /* #ifdef CONFIG_RCU_TRACE */
> -- 
> 1.8.1.5
> 

Re: [PATCH tip/core/rcu 13/13] rcu: Shrink TINY_RCU by reworking CPU-stall ifdefs

[Paul E. McKenney]

On Tue, May 21, 2013 at 10:31:41AM -0700, Josh Triplett wrote:
> On Mon, May 20, 2013 at 07:58:20AM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > 
> > TINY_RCU's reset_cpu_stall_ticks() and check_cpu_stalls() functions
> > are defined unconditionally, and are empty functions if CONFIG_RCU_TRACE
> > is disabled (which in turns disables detection of RCU CPU stalls).
> > These empty functions can add a bit of bloat to TINY_RCU, so this
> > commit reworks the ifdefs so that these functions are defined only
> > if they actually do something.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> Strange.  Both of these functions are static, and called in only one
> place, so shouldn't the compiler inline them (and thus throw them away
> completely when empty)?  Why does it not do so?

Good point for most architectures.  But given Tiny RCU's purpose, it
should allow for stupid compilers.  And I do need to fix the commit
message to call out the other benefit, namely saving a couple of
lines of source code.

							Thanx, Paul

> - Josh Triplett
> 
> > ---
> >  kernel/rcutiny.c        | 4 ++--
> >  kernel/rcutiny_plugin.h | 6 ++----
> >  2 files changed, 4 insertions(+), 6 deletions(-)
> > 
> > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
> > index 4adc9e2..aa34411 100644
> > --- a/kernel/rcutiny.c
> > +++ b/kernel/rcutiny.c
> > @@ -204,7 +204,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
> >   */
> >  static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
> >  {
> > -	reset_cpu_stall_ticks(rcp);
> > +	RCU_TRACE(reset_cpu_stall_ticks(rcp));
> >  	if (rcp->rcucblist != NULL &&
> >  	    rcp->donetail != rcp->curtail) {
> >  		rcp->donetail = rcp->curtail;
> > @@ -251,7 +251,7 @@ void rcu_bh_qs(int cpu)
> >   */
> >  void rcu_check_callbacks(int cpu, int user)
> >  {
> > -	check_cpu_stalls();
> > +	RCU_TRACE(check_cpu_stalls());
> >  	if (user || rcu_is_cpu_rrupt_from_idle())
> >  		rcu_sched_qs(cpu);
> >  	else if (!in_softirq())
> > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
> > index 65ef180..0cd385a 100644
> > --- a/kernel/rcutiny_plugin.h
> > +++ b/kernel/rcutiny_plugin.h
> > @@ -158,15 +158,11 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
> >  		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)
> > @@ -174,3 +170,5 @@ static void check_cpu_stalls(void)
> >  	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
> >  	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
> >  }
> > +
> > +#endif /* #ifdef CONFIG_RCU_TRACE */
> > -- 
> > 1.8.1.5
> > 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

Re: [PATCH tip/core/rcu 13/13] rcu: Shrink TINY_RCU by reworking CPU-stall ifdefs

[Josh Triplett]

On Tue, May 21, 2013 at 02:09:57PM -0700, Paul E. McKenney wrote:
> On Tue, May 21, 2013 at 10:31:41AM -0700, Josh Triplett wrote:
> > On Mon, May 20, 2013 at 07:58:20AM -0700, Paul E. McKenney wrote:
> > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > > 
> > > TINY_RCU's reset_cpu_stall_ticks() and check_cpu_stalls() functions
> > > are defined unconditionally, and are empty functions if CONFIG_RCU_TRACE
> > > is disabled (which in turns disables detection of RCU CPU stalls).
> > > These empty functions can add a bit of bloat to TINY_RCU, so this
> > > commit reworks the ifdefs so that these functions are defined only
> > > if they actually do something.
> > > 
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > 
> > Strange.  Both of these functions are static, and called in only one
> > place, so shouldn't the compiler inline them (and thus throw them away
> > completely when empty)?  Why does it not do so?
> 
> Good point for most architectures.  But given Tiny RCU's purpose, it
> should allow for stupid compilers.  And I do need to fix the commit
> message to call out the other benefit, namely saving a couple of
> lines of source code.

Regarding function inlining, at least, GCC is usually equally stupid on
all architectures.  I'd be quite surprised if any architecture actually
emits code for these functions.  You could also try changing them to
"static inline", in which case GCC should *definitely* never emit code
for them when empty.

- Josh Triplett

> 							Thanx, Paul
> 
> > - Josh Triplett
> > 
> > > ---
> > >  kernel/rcutiny.c        | 4 ++--
> > >  kernel/rcutiny_plugin.h | 6 ++----
> > >  2 files changed, 4 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
> > > index 4adc9e2..aa34411 100644
> > > --- a/kernel/rcutiny.c
> > > +++ b/kernel/rcutiny.c
> > > @@ -204,7 +204,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
> > >   */
> > >  static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
> > >  {
> > > -	reset_cpu_stall_ticks(rcp);
> > > +	RCU_TRACE(reset_cpu_stall_ticks(rcp));
> > >  	if (rcp->rcucblist != NULL &&
> > >  	    rcp->donetail != rcp->curtail) {
> > >  		rcp->donetail = rcp->curtail;
> > > @@ -251,7 +251,7 @@ void rcu_bh_qs(int cpu)
> > >   */
> > >  void rcu_check_callbacks(int cpu, int user)
> > >  {
> > > -	check_cpu_stalls();
> > > +	RCU_TRACE(check_cpu_stalls());
> > >  	if (user || rcu_is_cpu_rrupt_from_idle())
> > >  		rcu_sched_qs(cpu);
> > >  	else if (!in_softirq())
> > > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
> > > index 65ef180..0cd385a 100644
> > > --- a/kernel/rcutiny_plugin.h
> > > +++ b/kernel/rcutiny_plugin.h
> > > @@ -158,15 +158,11 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
> > >  		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)
> > > @@ -174,3 +170,5 @@ static void check_cpu_stalls(void)
> > >  	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
> > >  	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
> > >  }
> > > +
> > > +#endif /* #ifdef CONFIG_RCU_TRACE */
> > > -- 
> > > 1.8.1.5
> > > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> > 
>