/*

   * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra

   *
   * Provides a framework for enqueueing and running callbacks from hardirq
   * context. The enqueueing is NMI-safe.
   */

  #include <linux/bug.h>

  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/irq_work.h>

  #include <linux/percpu.h>

  #include <linux/hardirq.h>

  #include <linux/irqflags.h>

  #include <linux/sched.h>
  #include <linux/tick.h>

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

  #include <linux/smp.h>

  #include <asm/processor.h>

  static DEFINE_PER_CPU(struct llist_head, raised_list);
  static DEFINE_PER_CPU(struct llist_head, lazy_list);

  
  /*
   * Claim the entry so that no one else will poke at it.
   */

  static bool irq_work_claim(struct irq_work *work)

  {

  	unsigned long flags, oflags, nflags;

  	/*
  	 * Start with our best wish as a premise but only trust any
  	 * flag value after cmpxchg() result.
  	 */
  	flags = work->flags & ~IRQ_WORK_PENDING;

  	for (;;) {

  		nflags = flags | IRQ_WORK_FLAGS;

  		oflags = cmpxchg(&work->flags, flags, nflags);
  		if (oflags == flags)

  			break;

  		if (oflags & IRQ_WORK_PENDING)
  			return false;
  		flags = oflags;

  		cpu_relax();
  	}

  
  	return true;
  }

  void __weak arch_irq_work_raise(void)
  {
  	/*
  	 * Lame architectures will get the timer tick callback
  	 */
  }

  #ifdef CONFIG_SMP

  /*

   * Enqueue the irq_work @work on @cpu unless it's already pending

   * somewhere.
   *
   * Can be re-enqueued while the callback is still in progress.

   */

  bool irq_work_queue_on(struct irq_work *work, int cpu)
  {
  	/* All work should have been flushed before going offline */
  	WARN_ON_ONCE(cpu_is_offline(cpu));
  
  	/* Arch remote IPI send/receive backend aren't NMI safe */
  	WARN_ON_ONCE(in_nmi());
  
  	/* Only queue if not already pending */
  	if (!irq_work_claim(work))
  		return false;
  
  	if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
  		arch_send_call_function_single_ipi(cpu);
  
  	return true;
  }
  EXPORT_SYMBOL_GPL(irq_work_queue_on);
  #endif
  
  /* Enqueue the irq work @work on the current CPU */

  bool irq_work_queue(struct irq_work *work)

  {

  	/* Only queue if not already pending */
  	if (!irq_work_claim(work))

  		return false;

  
  	/* Queue the entry and raise the IPI if needed. */

  	preempt_disable();

  	/* If the work is "lazy", handle it from next tick if any */
  	if (work->flags & IRQ_WORK_LAZY) {

  		if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&

  		    tick_nohz_tick_stopped())
  			arch_irq_work_raise();
  	} else {

  		if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))

  			arch_irq_work_raise();
  	}

  	preempt_enable();

  
  	return true;

  }

  EXPORT_SYMBOL_GPL(irq_work_queue);

  bool irq_work_needs_cpu(void)
  {

  	struct llist_head *raised, *lazy;

  	raised = this_cpu_ptr(&raised_list);
  	lazy = this_cpu_ptr(&lazy_list);

  
  	if (llist_empty(raised) || arch_irq_work_has_interrupt())
  		if (llist_empty(lazy))
  			return false;

  	/* All work should have been flushed before going offline */
  	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));

  	return true;
  }

  static void irq_work_run_list(struct llist_head *list)

  {

  	unsigned long flags;

  	struct irq_work *work;

  	struct llist_node *llnode;

  	BUG_ON(!irqs_disabled());

  	if (llist_empty(list))

  		return;

  	llnode = llist_del_all(list);

  	while (llnode != NULL) {
  		work = llist_entry(llnode, struct irq_work, llnode);

  		llnode = llist_next(llnode);

  
  		/*

  		 * Clear the PENDING bit, after this point the @work

  		 * can be re-used.

  		 * Make it immediately visible so that other CPUs trying
  		 * to claim that work don't rely on us to handle their data
  		 * while we are in the middle of the func.

  		 */

  		flags = work->flags & ~IRQ_WORK_PENDING;
  		xchg(&work->flags, flags);

  		work->func(work);

  		/*
  		 * Clear the BUSY bit and return to the free state if
  		 * no-one else claimed it meanwhile.
  		 */

  		(void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);

  	}
  }

  
  /*

   * hotplug calls this through:
   *  hotplug_cfd() -> flush_smp_call_function_queue()

   */
  void irq_work_run(void)
  {

  	irq_work_run_list(this_cpu_ptr(&raised_list));
  	irq_work_run_list(this_cpu_ptr(&lazy_list));

  }

  EXPORT_SYMBOL_GPL(irq_work_run);

  void irq_work_tick(void)
  {

  	struct llist_head *raised = this_cpu_ptr(&raised_list);

  
  	if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
  		irq_work_run_list(raised);

  	irq_work_run_list(this_cpu_ptr(&lazy_list));

  }

  /*
   * Synchronize against the irq_work @entry, ensures the entry is not
   * currently in use.
   */

  void irq_work_sync(struct irq_work *work)

  {
  	WARN_ON_ONCE(irqs_disabled());

  	while (work->flags & IRQ_WORK_BUSY)

  		cpu_relax();
  }
  EXPORT_SYMBOL_GPL(irq_work_sync);