text: /*
   * Read-Copy Update mechanism for mutual exclusion
   *
   * 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 (C) IBM Corporation, 2001
   *
   * Authors: Dipankar Sarma <dipankar@in.ibm.com>
   *	    Manfred Spraul <manfred@colorfullife.com>
   * 
   * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
   * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
   * Papers:
   * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
   * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
   *
   * For detailed explanation of Read-Copy Update mechanism see -
   * 		http://lse.sourceforge.net/locking/rcupdate.html
   *
   */
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/spinlock.h>
  #include <linux/smp.h>
  #include <linux/rcupdate.h>
  #include <linux/interrupt.h>
  #include <linux/sched.h>
  #include <asm/atomic.h>
  #include <linux/bitops.h>
  #include <linux/module.h>
  #include <linux/completion.h>
  #include <linux/moduleparam.h>
  #include <linux/percpu.h>
  #include <linux/notifier.h>
  #include <linux/rcupdate.h>
  #include <linux/cpu.h>
  #include <linux/mutex.h>
  
  /* Definition for rcupdate control block. */
  static struct rcu_ctrlblk rcu_ctrlblk = {
  	.cur = -300,
  	.completed = -300,
  	.lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
  	.cpumask = CPU_MASK_NONE,
  };
  static struct rcu_ctrlblk rcu_bh_ctrlblk = {
  	.cur = -300,
  	.completed = -300,
  	.lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
  	.cpumask = CPU_MASK_NONE,
  };
  
  DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
  DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
  
  /* Fake initialization required by compiler */
  static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
  static int blimit = 10;
  static int qhimark = 10000;
  static int qlowmark = 100;
  
  static atomic_t rcu_barrier_cpu_count;
  static DEFINE_MUTEX(rcu_barrier_mutex);
  static struct completion rcu_barrier_completion;
  
  #ifdef CONFIG_SMP
  static void force_quiescent_state(struct rcu_data *rdp,
  			struct rcu_ctrlblk *rcp)
  {
  	int cpu;
  	cpumask_t cpumask;
  	set_need_resched();
  	if (unlikely(!rcp->signaled)) {
  		rcp->signaled = 1;
  		/*
  		 * Don't send IPI to itself. With irqs disabled,
  		 * rdp->cpu is the current cpu.
  		 */
  		cpumask = rcp->cpumask;
  		cpu_clear(rdp->cpu, cpumask);
  		for_each_cpu_mask(cpu, cpumask)
  			smp_send_reschedule(cpu);
  	}
  }
  #else
  static inline void force_quiescent_state(struct rcu_data *rdp,
  			struct rcu_ctrlblk *rcp)
  {
  	set_need_resched();
  }
  #endif
  
  /**
   * call_rcu - Queue an RCU callback for invocation after a grace period.
   * @head: structure to be used for queueing the RCU updates.
   * @func: actual update function to be invoked after the grace period
   *
   * The update function will be invoked some time after a full grace
   * period elapses, 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 fastcall call_rcu(struct rcu_head *head,
  				void (*func)(struct rcu_head *rcu))
  {
  	unsigned long flags;
  	struct rcu_data *rdp;
  
  	head->func = func;
  	head->next = NULL;
  	local_irq_save(flags);
  	rdp = &__get_cpu_var(rcu_data);
  	*rdp->nxttail = head;
  	rdp->nxttail = &head->next;
  	if (unlikely(++rdp->qlen > qhimark)) {
  		rdp->blimit = INT_MAX;
  		force_quiescent_state(rdp, &rcu_ctrlblk);
  	}
  	local_irq_restore(flags);
  }
  
  /**
   * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
   * @head: structure to be used for queueing the RCU updates.
   * @func: actual update function to be invoked after the grace period
   *
   * The update function will be invoked some time after a full grace
   * period elapses, in other words after all currently executing RCU
   * read-side critical sections have completed. call_rcu_bh() assumes
   * that the read-side critical sections end on completion of a softirq
   * handler. This means that read-side critical sections in process
   * context must not be interrupted by softirqs. This interface is to be
   * used when most of the read-side critical sections are in softirq context.
   * RCU read-side critical sections are delimited by rcu_read_lock() and
   * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
   * and rcu_read_unlock_bh(), if in process context. These may be nested.
   */
  void fastcall call_rcu_bh(struct rcu_head *head,
  				void (*func)(struct rcu_head *rcu))
  {
  	unsigned long flags;
  	struct rcu_data *rdp;
  
  	head->func = func;
  	head->next = NULL;
  	local_irq_save(flags);
  	rdp = &__get_cpu_var(rcu_bh_data);
  	*rdp->nxttail = head;
  	rdp->nxttail = &head->next;
  
  	if (unlikely(++rdp->qlen > qhimark)) {
  		rdp->blimit = INT_MAX;
  		force_quiescent_state(rdp, &rcu_bh_ctrlblk);
  	}
  
  	local_irq_restore(flags);
  }
  
  /*
   * Return the number of RCU batches processed thus far.  Useful
   * for debug and statistics.
   */
  long rcu_batches_completed(void)
  {
  	return rcu_ctrlblk.completed;
  }
  
  /*
   * Return the number of RCU batches processed thus far.  Useful
   * for debug and statistics.
   */
  long rcu_batches_completed_bh(void)
  {
  	return rcu_bh_ctrlblk.completed;
  }
  
  static void rcu_barrier_callback(struct rcu_head *notused)
  {
  	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
  		complete(&rcu_barrier_completion);
  }
  
  /*
   * Called with preemption disabled, and from cross-cpu IRQ context.
   */
  static void rcu_barrier_func(void *notused)
  {
  	int cpu = smp_processor_id();
  	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
  	struct rcu_head *head;
  
  	head = &rdp->barrier;
  	atomic_inc(&rcu_barrier_cpu_count);
  	call_rcu(head, rcu_barrier_callback);
  }
  
  /**
   * rcu_barrier - Wait until all the in-flight RCUs are complete.
   */
  void rcu_barrier(void)
  {
  	BUG_ON(in_interrupt());
  	/* Take cpucontrol mutex to protect against CPU hotplug */
  	mutex_lock(&rcu_barrier_mutex);
  	init_completion(&rcu_barrier_completion);
  	atomic_set(&rcu_barrier_cpu_count, 0);
  	on_each_cpu(rcu_barrier_func, NULL, 0, 1);
  	wait_for_completion(&rcu_barrier_completion);
  	mutex_unlock(&rcu_barrier_mutex);
  }
  EXPORT_SYMBOL_GPL(rcu_barrier);
  
  /*
   * Invoke the completed RCU callbacks. They are expected to be in
   * a per-cpu list.
   */
  static void rcu_do_batch(struct rcu_data *rdp)
  {
  	struct rcu_head *next, *list;
  	int count = 0;
  
  	list = rdp->donelist;
  	while (list) {
  		next = list->next;
  		prefetch(next);
  		list->func(list);
  		list = next;
  		if (++count >= rdp->blimit)
  			break;
  	}
  	rdp->donelist = list;
  
  	local_irq_disable();
  	rdp->qlen -= count;
  	local_irq_enable();
  	if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
  		rdp->blimit = blimit;
  
  	if (!rdp->donelist)
  		rdp->donetail = &rdp->donelist;
  	else
  		tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
  }
  
  /*
   * Grace period handling:
   * The grace period handling consists out of two steps:
   * - A new grace period is started.
   *   This is done by rcu_start_batch. The start is not broadcasted to
   *   all cpus, they must pick this up by comparing rcp->cur with
   *   rdp->quiescbatch. All cpus are recorded  in the
   *   rcu_ctrlblk.cpumask bitmap.
   * - All cpus must go through a quiescent state.
   *   Since the start of the grace period is not broadcasted, at least two
   *   calls to rcu_check_quiescent_state are required:
   *   The first call just notices that a new grace period is running. The
   *   following calls check if there was a quiescent state since the beginning
   *   of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
   *   the bitmap is empty, then the grace period is completed.
   *   rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
   *   period (if necessary).
   */
  /*
   * Register a new batch of callbacks, and start it up if there is currently no
   * active batch and the batch to be registered has not already occurred.
   * Caller must hold rcu_ctrlblk.lock.
   */
  static void rcu_start_batch(struct rcu_ctrlblk *rcp)
  {
  	if (rcp->next_pending &&
  			rcp->completed == rcp->cur) {
  		rcp->next_pending = 0;
  		/*
  		 * next_pending == 0 must be visible in
  		 * __rcu_process_callbacks() before it can see new value of cur.
  		 */
  		smp_wmb();
  		rcp->cur++;
  
  		/*
  		 * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
  		 * Barrier  Otherwise it can cause tickless idle CPUs to be
  		 * included in rcp->cpumask, which will extend graceperiods
  		 * unnecessarily.
  		 */
  		smp_mb();
  		cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
  
  		rcp->signaled = 0;
  	}
  }
  
  /*
   * cpu went through a quiescent state since the beginning of the grace period.
   * Clear it from the cpu mask and complete the grace period if it was the last
   * cpu. Start another grace period if someone has further entries pending
   */
  static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
  {
  	cpu_clear(cpu, rcp->cpumask);
  	if (cpus_empty(rcp->cpumask)) {
  		/* batch completed ! */
  		rcp->completed = rcp->cur;
  		rcu_start_batch(rcp);
  	}
  }
  
  /*
   * Check if the cpu has gone through a quiescent state (say context
   * switch). If so and if it already hasn't done so in this RCU
   * quiescent cycle, then indicate that it has done so.
   */
  static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
  					struct rcu_data *rdp)
  {
  	if (rdp->quiescbatch != rcp->cur) {
  		/* start new grace period: */
  		rdp->qs_pending = 1;
  		rdp->passed_quiesc = 0;
  		rdp->quiescbatch = rcp->cur;
  		return;
  	}
  
  	/* Grace period already completed for this cpu?
  	 * qs_pending is checked instead of the actual bitmap to avoid
  	 * cacheline trashing.
  	 */
  	if (!rdp->qs_pending)
  		return;
  
  	/* 
  	 * Was there a quiescent state since the beginning of the grace
  	 * period? If no, then exit and wait for the next call.
  	 */
  	if (!rdp->passed_quiesc)
  		return;
  	rdp->qs_pending = 0;
  
  	spin_lock(&rcp->lock);
  	/*
  	 * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
  	 * during cpu startup. Ignore the quiescent state.
  	 */
  	if (likely(rdp->quiescbatch == rcp->cur))
  		cpu_quiet(rdp->cpu, rcp);
  
  	spin_unlock(&rcp->lock);
  }
  
  
  #ifdef CONFIG_HOTPLUG_CPU
  
  /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
   * locking requirements, the list it's pulling from has to belong to a cpu
   * which is dead and hence not processing interrupts.
   */
  static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
  				struct rcu_head **tail)
  {
  	local_irq_disable();
  	*this_rdp->nxttail = list;
  	if (list)
  		this_rdp->nxttail = tail;
  	local_irq_enable();
  }
  
  static void __rcu_offline_cpu(struct rcu_data *this_rdp,
  				struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
  {
  	/* if the cpu going offline owns the grace period
  	 * we can block indefinitely waiting for it, so flush
  	 * it here
  	 */
  	spin_lock_bh(&rcp->lock);
  	if (rcp->cur != rcp->completed)
  		cpu_quiet(rdp->cpu, rcp);
  	spin_unlock_bh(&rcp->lock);
  	rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
  	rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
  	rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
  }
  
  static void rcu_offline_cpu(int cpu)
  {
  	struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
  	struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
  
  	__rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
  					&per_cpu(rcu_data, cpu));
  	__rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
  					&per_cpu(rcu_bh_data, cpu));
  	put_cpu_var(rcu_data);
  	put_cpu_var(rcu_bh_data);
  	tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
  }
  
  #else
  
  static void rcu_offline_cpu(int cpu)
  {
  }
  
  #endif
  
  /*
   * This does the RCU processing work from tasklet context. 
   */
  static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
  					struct rcu_data *rdp)
  {
  	if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
  		*rdp->donetail = rdp->curlist;
  		rdp->donetail = rdp->curtail;
  		rdp->curlist = NULL;
  		rdp->curtail = &rdp->curlist;
  	}
  
  	if (rdp->nxtlist && !rdp->curlist) {
  		local_irq_disable();
  		rdp->curlist = rdp->nxtlist;
  		rdp->curtail = rdp->nxttail;
  		rdp->nxtlist = NULL;
  		rdp->nxttail = &rdp->nxtlist;
  		local_irq_enable();
  
  		/*
  		 * start the next batch of callbacks
  		 */
  
  		/* determine batch number */
  		rdp->batch = rcp->cur + 1;
  		/* see the comment and corresponding wmb() in
  		 * the rcu_start_batch()
  		 */
  		smp_rmb();
  
  		if (!rcp->next_pending) {
  			/* and start it/schedule start if it's a new batch */
  			spin_lock(&rcp->lock);
  			rcp->next_pending = 1;
  			rcu_start_batch(rcp);
  			spin_unlock(&rcp->lock);
  		}
  	}
  
  	rcu_check_quiescent_state(rcp, rdp);
  	if (rdp->donelist)
  		rcu_do_batch(rdp);
  }
  
  static void rcu_process_callbacks(unsigned long unused)
  {
  	__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
  	__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
  }
  
  static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
  {
  	/* This cpu has pending rcu entries and the grace period
  	 * for them has completed.
  	 */
  	if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
  		return 1;
  
  	/* This cpu has no pending entries, but there are new entries */
  	if (!rdp->curlist && rdp->nxtlist)
  		return 1;
  
  	/* This cpu has finished callbacks to invoke */
  	if (rdp->donelist)
  		return 1;
  
  	/* The rcu core waits for a quiescent state from the cpu */
  	if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
  		return 1;
  
  	/* nothing to do */
  	return 0;
  }
  
  /*
   * Check to see if there is any immediate RCU-related work to be done
   * by the current CPU, returning 1 if so.  This function is part of the
   * RCU implementation; it is -not- an exported member of the RCU API.
   */
  int rcu_pending(int cpu)
  {
  	return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
  		__rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
  }
  
  /*
   * Check to see if any future RCU-related work will need to be done
   * by the current CPU, even if none need be done immediately, returning
   * 1 if so.  This function is part of the RCU implementation; it is -not-
   * an exported member of the RCU API.
   */
  int rcu_needs_cpu(int cpu)
  {
  	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
  	struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
  
  	return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
  }
  
  void rcu_check_callbacks(int cpu, int user)
  {
  	if (user || 
  	    (idle_cpu(cpu) && !in_softirq() && 
  				hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
  		rcu_qsctr_inc(cpu);
  		rcu_bh_qsctr_inc(cpu);
  	} else if (!in_softirq())
  		rcu_bh_qsctr_inc(cpu);
  	tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
  }
  
  static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
  						struct rcu_data *rdp)
  {
  	memset(rdp, 0, sizeof(*rdp));
  	rdp->curtail = &rdp->curlist;
  	rdp->nxttail = &rdp->nxtlist;
  	rdp->donetail = &rdp->donelist;
  	rdp->quiescbatch = rcp->completed;
  	rdp->qs_pending = 0;
  	rdp->cpu = cpu;
  	rdp->blimit = blimit;
  }
  
  static void __devinit rcu_online_cpu(int cpu)
  {
  	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
  	struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
  
  	rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
  	rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
  	tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
  }
  
  static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
  				unsigned long action, void *hcpu)
  {
  	long cpu = (long)hcpu;
  	switch (action) {
  	case CPU_UP_PREPARE:
  		rcu_online_cpu(cpu);
  		break;
  	case CPU_DEAD:
  		rcu_offline_cpu(cpu);
  		break;
  	default:
  		break;
  	}
  	return NOTIFY_OK;
  }
  
  static struct notifier_block __cpuinitdata rcu_nb = {
  	.notifier_call	= rcu_cpu_notify,
  };
  
  /*
   * Initializes rcu mechanism.  Assumed to be called early.
   * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
   * Note that rcu_qsctr and friends are implicitly
   * initialized due to the choice of ``0'' for RCU_CTR_INVALID.
   */
  void __init rcu_init(void)
  {
  	rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
  			(void *)(long)smp_processor_id());
  	/* Register notifier for non-boot CPUs */
  	register_cpu_notifier(&rcu_nb);
  }
  
  struct rcu_synchronize {
  	struct rcu_head head;
  	struct completion completion;
  };
  
  /* Because of FASTCALL declaration of complete, we use this wrapper */
  static void wakeme_after_rcu(struct rcu_head  *head)
  {
  	struct rcu_synchronize *rcu;
  
  	rcu = container_of(head, struct rcu_synchronize, head);
  	complete(&rcu->completion);
  }
  
  /**
   * 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.
   *
   * If your read-side code is not protected by rcu_read_lock(), do -not-
   * use synchronize_rcu().
   */
  void synchronize_rcu(void)
  {
  	struct rcu_synchronize rcu;
  
  	init_completion(&rcu.completion);
  	/* Will wake me after RCU finished */
  	call_rcu(&rcu.head, wakeme_after_rcu);
  
  	/* Wait for it */
  	wait_for_completion(&rcu.completion);
  }
  
  module_param(blimit, int, 0);
  module_param(qhimark, int, 0);
  module_param(qlowmark, int, 0);
  EXPORT_SYMBOL_GPL(rcu_batches_completed);
  EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
  EXPORT_SYMBOL_GPL(call_rcu);
  EXPORT_SYMBOL_GPL(call_rcu_bh);
  EXPORT_SYMBOL_GPL(synchronize_rcu);
  