/*
   * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   *
   * Copyright IBM Corporation, 2008
   *
   * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
   *
   * For detailed explanation of Read-Copy Update mechanism see -

   *		Documentation/RCU

   */

  #include <linux/completion.h>
  #include <linux/interrupt.h>

  #include <linux/notifier.h>

  #include <linux/rcupdate.h>
  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/mutex.h>

  #include <linux/sched.h>
  #include <linux/types.h>
  #include <linux/init.h>

  #include <linux/time.h>

  #include <linux/cpu.h>

  #include <linux/prefetch.h>

  #ifdef CONFIG_RCU_TRACE

  #include <trace/events/rcu.h>

  #endif /* #else #ifdef CONFIG_RCU_TRACE */
  
  #include "rcu.h"

  /* 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,
  		       void (*func)(struct rcu_head *rcu),
  		       struct rcu_ctrlblk *rcp);
  
  #include "rcutiny_plugin.h"

  static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;

  /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */

  static void rcu_idle_enter_common(long long oldval)

  {
  	if (rcu_dynticks_nesting) {

  		RCU_TRACE(trace_rcu_dyntick("--=",
  					    oldval, rcu_dynticks_nesting));

  		return;
  	}

  	RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));

  	if (!is_idle_task(current)) {

  		struct task_struct *idle = idle_task(smp_processor_id());

  		RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",

  					    oldval, rcu_dynticks_nesting));

  		ftrace_dump(DUMP_ALL);

  		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
  			  current->pid, current->comm,
  			  idle->pid, idle->comm); /* must be idle task! */

  	}
  	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
  }
  
  /*
   * Enter idle, which is an extended quiescent state if we have fully
   * entered that mode (i.e., if the new value of dynticks_nesting is zero).
   */
  void rcu_idle_enter(void)
  {
  	unsigned long flags;

  	long long oldval;

  
  	local_irq_save(flags);

  	oldval = rcu_dynticks_nesting;

  	rcu_dynticks_nesting = 0;

  	rcu_idle_enter_common(oldval);

  	local_irq_restore(flags);
  }
  
  /*
   * Exit an interrupt handler towards idle.
   */
  void rcu_irq_exit(void)
  {
  	unsigned long flags;

  	long long oldval;

  
  	local_irq_save(flags);

  	oldval = rcu_dynticks_nesting;

  	rcu_dynticks_nesting--;
  	WARN_ON_ONCE(rcu_dynticks_nesting < 0);

  	rcu_idle_enter_common(oldval);

  	local_irq_restore(flags);
  }
  
  /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
  static void rcu_idle_exit_common(long long oldval)
  {
  	if (oldval) {

  		RCU_TRACE(trace_rcu_dyntick("++=",
  					    oldval, rcu_dynticks_nesting));

  		return;
  	}

  	RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));

  	if (!is_idle_task(current)) {

  		struct task_struct *idle = idle_task(smp_processor_id());

  		RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",

  			  oldval, rcu_dynticks_nesting));

  		ftrace_dump(DUMP_ALL);

  		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
  			  current->pid, current->comm,
  			  idle->pid, idle->comm); /* must be idle task! */

  	}
  }

  
  /*

   * Exit idle, so that we are no longer in an extended quiescent state.

   */

  void rcu_idle_exit(void)

  {

  	unsigned long flags;
  	long long oldval;
  
  	local_irq_save(flags);
  	oldval = rcu_dynticks_nesting;
  	WARN_ON_ONCE(oldval != 0);

  	rcu_dynticks_nesting = DYNTICK_TASK_NESTING;

  	rcu_idle_exit_common(oldval);
  	local_irq_restore(flags);

  }
  
  /*

   * Enter an interrupt handler, moving away from idle.

   */

  void rcu_irq_enter(void)

  {

  	unsigned long flags;
  	long long oldval;
  
  	local_irq_save(flags);
  	oldval = rcu_dynticks_nesting;

  	rcu_dynticks_nesting++;

  	WARN_ON_ONCE(rcu_dynticks_nesting == 0);
  	rcu_idle_exit_common(oldval);
  	local_irq_restore(flags);

  }

  #ifdef CONFIG_PROVE_RCU
  
  /*
   * Test whether RCU thinks that the current CPU is idle.
   */
  int rcu_is_cpu_idle(void)
  {
  	return !rcu_dynticks_nesting;
  }

  EXPORT_SYMBOL(rcu_is_cpu_idle);

  
  #endif /* #ifdef CONFIG_PROVE_RCU */
  
  /*
   * Test whether the current CPU was interrupted from idle.  Nested
   * interrupts don't count, we must be running at the first interrupt
   * level.
   */
  int rcu_is_cpu_rrupt_from_idle(void)
  {
  	return rcu_dynticks_nesting <= 0;
  }

  
  /*

   * Helper function for rcu_sched_qs() and rcu_bh_qs().
   * Also irqs are disabled to avoid confusion due to interrupt handlers

   * invoking call_rcu().

   */
  static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  {

  	if (rcp->rcucblist != NULL &&
  	    rcp->donetail != rcp->curtail) {
  		rcp->donetail = rcp->curtail;

  		return 1;
  	}

  	return 0;
  }
  
  /*
   * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
   * are at it, given that any rcu quiescent state is also an rcu_bh
   * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
   */
  void rcu_sched_qs(int cpu)
  {

  	unsigned long flags;
  
  	local_irq_save(flags);

  	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
  	    rcu_qsctr_help(&rcu_bh_ctrlblk))

  		invoke_rcu_callbacks();

  	local_irq_restore(flags);

  }
  
  /*
   * Record an rcu_bh quiescent state.
   */
  void rcu_bh_qs(int cpu)
  {

  	unsigned long flags;
  
  	local_irq_save(flags);

  	if (rcu_qsctr_help(&rcu_bh_ctrlblk))

  		invoke_rcu_callbacks();

  	local_irq_restore(flags);

  }
  
  /*
   * Check to see if the scheduling-clock interrupt came from an extended

   * quiescent state, and, if so, tell RCU about it.  This function must
   * be called from hardirq context.  It is normally called from the
   * scheduling-clock interrupt.

   */
  void rcu_check_callbacks(int cpu, int user)
  {

  	if (user || rcu_is_cpu_rrupt_from_idle())

  		rcu_sched_qs(cpu);
  	else if (!in_softirq())
  		rcu_bh_qs(cpu);

  	rcu_preempt_check_callbacks();

  }
  
  /*

   * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
   * whose grace period has elapsed.

   */

  static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)

  {

  	char *rn = NULL;

  	struct rcu_head *next, *list;

  	unsigned long flags;

  	RCU_TRACE(int cb_count = 0);

  
  	/* If no RCU callbacks ready to invoke, just return. */

  	if (&rcp->rcucblist == rcp->donetail) {

  		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));

  		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
  					      ACCESS_ONCE(rcp->rcucblist),
  					      need_resched(),
  					      is_idle_task(current),
  					      rcu_is_callbacks_kthread()));

  		return;

  	}

  
  	/* Move the ready-to-invoke callbacks to a local list. */
  	local_irq_save(flags);

  	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));

  	list = rcp->rcucblist;
  	rcp->rcucblist = *rcp->donetail;
  	*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);
  
  	/* Invoke the callbacks on the local list. */

  	RCU_TRACE(rn = rcp->name);

  	while (list) {
  		next = list->next;
  		prefetch(next);

  		debug_rcu_head_unqueue(list);

  		local_bh_disable();

  		__rcu_reclaim(rn, list);

  		local_bh_enable();

  		list = next;

  		RCU_TRACE(cb_count++);

  	}

  	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()));

  }

  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();

  }
  
  /*

   * Wait for a grace period to elapse.  But it is illegal to invoke
   * synchronize_sched() from within an RCU read-side critical section.
   * Therefore, any legal call to synchronize_sched() is a quiescent
   * state, and so on a UP system, synchronize_sched() need do nothing.
   * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
   * benefits of doing might_sleep() to reduce latency.)
   *
   * Cool, huh?  (Due to Josh Triplett.)
   *

   * But we want to make this a static inline later.  The cond_resched()
   * currently makes this problematic.

   */
  void synchronize_sched(void)
  {
  	cond_resched();
  }
  EXPORT_SYMBOL_GPL(synchronize_sched);

  /*
   * Helper function for call_rcu() and call_rcu_bh().
   */
  static void __call_rcu(struct rcu_head *head,
  		       void (*func)(struct rcu_head *rcu),
  		       struct rcu_ctrlblk *rcp)
  {
  	unsigned long flags;

  	debug_rcu_head_queue(head);

  	head->func = func;
  	head->next = NULL;

  	local_irq_save(flags);
  	*rcp->curtail = head;
  	rcp->curtail = &head->next;

  	RCU_TRACE(rcp->qlen++);

  	local_irq_restore(flags);
  }
  
  /*

   * Post an RCU callback to be invoked after the end of an RCU-sched grace

   * period.  But since we have but one CPU, that would be after any
   * quiescent state.
   */

  void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))

  {

  	__call_rcu(head, func, &rcu_sched_ctrlblk);

  }

  EXPORT_SYMBOL_GPL(call_rcu_sched);

  
  /*
   * Post an RCU bottom-half callback to be invoked after any subsequent
   * quiescent state.
   */

  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);