// SPDX-License-Identifier: GPL-2.0+

  /*
   * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
   *

   * Copyright IBM Corporation, 2008
   *

   * Author: Paul E. McKenney <paulmck@linux.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_wait.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>

  #include <linux/slab.h>

  #include <linux/mm.h>

  #include "rcu.h"

  /* Global control variables for rcupdate callback mechanism. */
  struct rcu_ctrlblk {
  	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
  	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
  	struct rcu_head **curtail;	/* ->next pointer of last CB. */
  };
  
  /* Definition for rcupdate control block. */

  static struct rcu_ctrlblk rcu_ctrlblk = {
  	.donetail	= &rcu_ctrlblk.rcucblist,
  	.curtail	= &rcu_ctrlblk.rcucblist,

  };

  void rcu_barrier(void)

  {

  	wait_rcu_gp(call_rcu);

  }

  EXPORT_SYMBOL(rcu_barrier);

  /* Record an rcu quiescent state.  */

  void rcu_qs(void)

  {

  	unsigned long flags;
  
  	local_irq_save(flags);

  	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
  		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;

  		raise_softirq_irqoff(RCU_SOFTIRQ);

  	}

  	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_sched_clock_irq(int user)

  {

  	if (user) {

  		rcu_qs();

  	} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
  		set_tsk_need_resched(current);
  		set_preempt_need_resched();
  	}

  }

  /*
   * Reclaim the specified callback, either by invoking it for non-kfree cases or
   * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
   */
  static inline bool rcu_reclaim_tiny(struct rcu_head *head)
  {
  	rcu_callback_t f;
  	unsigned long offset = (unsigned long)head->func;
  
  	rcu_lock_acquire(&rcu_callback_map);

  	if (__is_kvfree_rcu_offset(offset)) {
  		trace_rcu_invoke_kvfree_callback("", head, offset);

  		kvfree((void *)head - offset);

  		rcu_lock_release(&rcu_callback_map);
  		return true;
  	}
  
  	trace_rcu_invoke_callback("", head);
  	f = head->func;
  	WRITE_ONCE(head->func, (rcu_callback_t)0L);
  	f(head);
  	rcu_lock_release(&rcu_callback_map);
  	return false;
  }

  /* Invoke the RCU callbacks whose grace period has elapsed.  */
  static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)

  {

  	struct rcu_head *next, *list;

  	unsigned long flags;

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

  	if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {

  		/* No callbacks ready, so just leave. */
  		local_irq_restore(flags);
  		return;
  	}

  	list = rcu_ctrlblk.rcucblist;
  	rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
  	*rcu_ctrlblk.donetail = NULL;
  	if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
  		rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
  	rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;

  	local_irq_restore(flags);
  
  	/* Invoke the callbacks on the local list. */
  	while (list) {
  		next = list->next;
  		prefetch(next);

  		debug_rcu_head_unqueue(list);

  		local_bh_disable();

  		rcu_reclaim_tiny(list);

  		local_bh_enable();

  		list = next;
  	}
  }

  /*

   * Wait for a grace period to elapse.  But it is illegal to invoke

   * synchronize_rcu() from within an RCU read-side critical section.
   * Therefore, any legal call to synchronize_rcu() is a quiescent
   * state, and so on a UP system, synchronize_rcu() need do nothing.

   * (But Lai Jiangshan points out the benefits of doing might_sleep()
   * to reduce latency.)

   *
   * Cool, huh?  (Due to Josh Triplett.)

   */

  void synchronize_rcu(void)

  {

  	RCU_LOCKDEP_WARN(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");

  }

  EXPORT_SYMBOL_GPL(synchronize_rcu);

  /*

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

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

   */

  void call_rcu(struct rcu_head *head, rcu_callback_t func)

  {
  	unsigned long flags;

  	debug_rcu_head_queue(head);

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

  	local_irq_save(flags);

  	*rcu_ctrlblk.curtail = head;
  	rcu_ctrlblk.curtail = &head->next;

  	local_irq_restore(flags);

  
  	if (unlikely(is_idle_task(current))) {

  		/* force scheduling for rcu_qs() */

  		resched_cpu(0);
  	}

  }

  EXPORT_SYMBOL_GPL(call_rcu);

  void __init rcu_init(void)

  {
  	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);

  	rcu_early_boot_tests();

  	srcu_init();

  }