/*
   * 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 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/interrupt.h>
  #include <linux/sched.h>

  #include <linux/atomic.h>

  #include <linux/bitops.h>

  #include <linux/percpu.h>
  #include <linux/notifier.h>

  #include <linux/cpu.h>

  #include <linux/mutex.h>

  #include <linux/export.h>

  #include <linux/hardirq.h>

  #include <linux/delay.h>

  #include <linux/module.h>

  #define CREATE_TRACE_POINTS
  #include <trace/events/rcu.h>
  
  #include "rcu.h"

  module_param(rcu_expedited, int, 0);

  #ifdef CONFIG_PREEMPT_RCU
  
  /*

   * Preemptible RCU implementation for rcu_read_lock().
   * Just increment ->rcu_read_lock_nesting, shared state will be updated
   * if we block.
   */
  void __rcu_read_lock(void)
  {
  	current->rcu_read_lock_nesting++;
  	barrier();  /* critical section after entry code. */
  }
  EXPORT_SYMBOL_GPL(__rcu_read_lock);
  
  /*
   * Preemptible RCU implementation for rcu_read_unlock().
   * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
   * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
   * invoke rcu_read_unlock_special() to clean up after a context switch
   * in an RCU read-side critical section and other special cases.
   */
  void __rcu_read_unlock(void)
  {
  	struct task_struct *t = current;
  
  	if (t->rcu_read_lock_nesting != 1) {
  		--t->rcu_read_lock_nesting;
  	} else {
  		barrier();  /* critical section before exit code. */
  		t->rcu_read_lock_nesting = INT_MIN;

  #ifdef CONFIG_PROVE_RCU_DELAY
  		udelay(10); /* Make preemption more probable. */
  #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */

  		barrier();  /* assign before ->rcu_read_unlock_special load */
  		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  			rcu_read_unlock_special(t);
  		barrier();  /* ->rcu_read_unlock_special load before assign */
  		t->rcu_read_lock_nesting = 0;
  	}
  #ifdef CONFIG_PROVE_LOCKING
  	{
  		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
  
  		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
  	}
  #endif /* #ifdef CONFIG_PROVE_LOCKING */
  }
  EXPORT_SYMBOL_GPL(__rcu_read_unlock);

  #endif /* #ifdef CONFIG_PREEMPT_RCU */

  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  static struct lock_class_key rcu_lock_key;
  struct lockdep_map rcu_lock_map =
  	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  EXPORT_SYMBOL_GPL(rcu_lock_map);

  
  static struct lock_class_key rcu_bh_lock_key;
  struct lockdep_map rcu_bh_lock_map =
  	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  
  static struct lock_class_key rcu_sched_lock_key;
  struct lockdep_map rcu_sched_lock_map =
  	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  EXPORT_SYMBOL_GPL(rcu_sched_lock_map);

  int debug_lockdep_rcu_enabled(void)
  {
  	return rcu_scheduler_active && debug_locks &&
  	       current->lockdep_recursion == 0;
  }
  EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);

  /**

   * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?

   *
   * Check for bottom half being disabled, which covers both the
   * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
   * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)

   * will show the situation.  This is useful for debug checks in functions
   * that require that they be called within an RCU read-side critical
   * section.

   *
   * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.

   *
   * Note that rcu_read_lock() is disallowed if the CPU is either idle or
   * offline from an RCU perspective, so check for those as well.

   */
  int rcu_read_lock_bh_held(void)
  {
  	if (!debug_lockdep_rcu_enabled())
  		return 1;

  	if (rcu_is_cpu_idle())
  		return 0;

  	if (!rcu_lockdep_current_cpu_online())
  		return 0;

  	return in_softirq() || irqs_disabled();

  }
  EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
  
  #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

  struct rcu_synchronize {
  	struct rcu_head head;
  	struct completion completion;
  };

  /*

   * Awaken the corresponding synchronize_rcu() instance now that a
   * grace period has elapsed.
   */

  static void wakeme_after_rcu(struct rcu_head  *head)

  {

  	struct rcu_synchronize *rcu;
  
  	rcu = container_of(head, struct rcu_synchronize, head);
  	complete(&rcu->completion);

  }

  void wait_rcu_gp(call_rcu_func_t crf)
  {
  	struct rcu_synchronize rcu;
  
  	init_rcu_head_on_stack(&rcu.head);
  	init_completion(&rcu.completion);
  	/* Will wake me after RCU finished. */
  	crf(&rcu.head, wakeme_after_rcu);
  	/* Wait for it. */
  	wait_for_completion(&rcu.completion);
  	destroy_rcu_head_on_stack(&rcu.head);
  }
  EXPORT_SYMBOL_GPL(wait_rcu_gp);

  #ifdef CONFIG_PROVE_RCU
  /*
   * wrapper function to avoid #include problems.
   */
  int rcu_my_thread_group_empty(void)
  {
  	return thread_group_empty(current);
  }
  EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
  #endif /* #ifdef CONFIG_PROVE_RCU */

  
  #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
  static inline void debug_init_rcu_head(struct rcu_head *head)
  {
  	debug_object_init(head, &rcuhead_debug_descr);
  }
  
  static inline void debug_rcu_head_free(struct rcu_head *head)
  {
  	debug_object_free(head, &rcuhead_debug_descr);
  }
  
  /*
   * fixup_init is called when:
   * - an active object is initialized
   */
  static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
  {
  	struct rcu_head *head = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		/*
  		 * Ensure that queued callbacks are all executed.
  		 * If we detect that we are nested in a RCU read-side critical
  		 * section, we should simply fail, otherwise we would deadlock.

  		 * In !PREEMPT configurations, there is no way to tell if we are
  		 * in a RCU read-side critical section or not, so we never
  		 * attempt any fixup and just print a warning.

  		 */

  #ifndef CONFIG_PREEMPT

  		WARN_ON_ONCE(1);

  		return 0;
  #endif

  		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
  		    irqs_disabled()) {

  			WARN_ON_ONCE(1);

  			return 0;
  		}
  		rcu_barrier();
  		rcu_barrier_sched();
  		rcu_barrier_bh();
  		debug_object_init(head, &rcuhead_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  /*
   * fixup_activate is called when:
   * - an active object is activated
   * - an unknown object is activated (might be a statically initialized object)
   * Activation is performed internally by call_rcu().
   */
  static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
  {
  	struct rcu_head *head = addr;
  
  	switch (state) {
  
  	case ODEBUG_STATE_NOTAVAILABLE:
  		/*
  		 * This is not really a fixup. We just make sure that it is
  		 * tracked in the object tracker.
  		 */
  		debug_object_init(head, &rcuhead_debug_descr);
  		debug_object_activate(head, &rcuhead_debug_descr);
  		return 0;
  
  	case ODEBUG_STATE_ACTIVE:
  		/*
  		 * Ensure that queued callbacks are all executed.
  		 * If we detect that we are nested in a RCU read-side critical
  		 * section, we should simply fail, otherwise we would deadlock.

  		 * In !PREEMPT configurations, there is no way to tell if we are
  		 * in a RCU read-side critical section or not, so we never
  		 * attempt any fixup and just print a warning.

  		 */

  #ifndef CONFIG_PREEMPT

  		WARN_ON_ONCE(1);

  		return 0;
  #endif

  		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
  		    irqs_disabled()) {

  			WARN_ON_ONCE(1);

  			return 0;
  		}
  		rcu_barrier();
  		rcu_barrier_sched();
  		rcu_barrier_bh();
  		debug_object_activate(head, &rcuhead_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  /*
   * fixup_free is called when:
   * - an active object is freed
   */
  static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
  {
  	struct rcu_head *head = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		/*
  		 * Ensure that queued callbacks are all executed.
  		 * If we detect that we are nested in a RCU read-side critical
  		 * section, we should simply fail, otherwise we would deadlock.

  		 * In !PREEMPT configurations, there is no way to tell if we are
  		 * in a RCU read-side critical section or not, so we never
  		 * attempt any fixup and just print a warning.

  		 */

  #ifndef CONFIG_PREEMPT

  		WARN_ON_ONCE(1);

  		return 0;
  #endif

  		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
  		    irqs_disabled()) {

  			WARN_ON_ONCE(1);

  			return 0;
  		}
  		rcu_barrier();
  		rcu_barrier_sched();
  		rcu_barrier_bh();
  		debug_object_free(head, &rcuhead_debug_descr);
  		return 1;

  	default:
  		return 0;
  	}
  }
  
  /**
   * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
   * @head: pointer to rcu_head structure to be initialized
   *
   * This function informs debugobjects of a new rcu_head structure that
   * has been allocated as an auto variable on the stack.  This function
   * is not required for rcu_head structures that are statically defined or
   * that are dynamically allocated on the heap.  This function has no
   * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
   */
  void init_rcu_head_on_stack(struct rcu_head *head)
  {
  	debug_object_init_on_stack(head, &rcuhead_debug_descr);
  }
  EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
  
  /**
   * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
   * @head: pointer to rcu_head structure to be initialized
   *
   * This function informs debugobjects that an on-stack rcu_head structure
   * is about to go out of scope.  As with init_rcu_head_on_stack(), this
   * function is not required for rcu_head structures that are statically
   * defined or that are dynamically allocated on the heap.  Also as with
   * init_rcu_head_on_stack(), this function has no effect for
   * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
   */
  void destroy_rcu_head_on_stack(struct rcu_head *head)
  {
  	debug_object_free(head, &rcuhead_debug_descr);
  }
  EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
  
  struct debug_obj_descr rcuhead_debug_descr = {
  	.name = "rcu_head",
  	.fixup_init = rcuhead_fixup_init,
  	.fixup_activate = rcuhead_fixup_activate,
  	.fixup_free = rcuhead_fixup_free,
  };
  EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
  #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

  
  #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)

  void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,
  			       unsigned long secs,
  			       unsigned long c_old, unsigned long c)

  {

  	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);

  }
  EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
  #else

  #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
  	do { } while (0)

  #endif

  
  #ifdef CONFIG_RCU_STALL_COMMON
  
  #ifdef CONFIG_PROVE_RCU
  #define RCU_STALL_DELAY_DELTA	       (5 * HZ)
  #else
  #define RCU_STALL_DELAY_DELTA	       0
  #endif
  
  int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
  int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
  
  module_param(rcu_cpu_stall_suppress, int, 0644);
  module_param(rcu_cpu_stall_timeout, int, 0644);
  
  int rcu_jiffies_till_stall_check(void)
  {
  	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
  
  	/*
  	 * Limit check must be consistent with the Kconfig limits
  	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
  	 */
  	if (till_stall_check < 3) {
  		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
  		till_stall_check = 3;
  	} else if (till_stall_check > 300) {
  		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
  		till_stall_check = 300;
  	}
  	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
  }
  
  static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
  {
  	rcu_cpu_stall_suppress = 1;
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block rcu_panic_block = {
  	.notifier_call = rcu_panic,
  };
  
  static int __init check_cpu_stall_init(void)
  {
  	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
  	return 0;
  }
  early_initcall(check_cpu_stall_init);
  
  #endif /* #ifdef CONFIG_RCU_STALL_COMMON */