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

  /*

   * 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)

  {

  	int oflags;

  	oflags = atomic_fetch_or(IRQ_WORK_CLAIMED | CSD_TYPE_IRQ_WORK, &work->flags);

  	/*

  	 * If the work is already pending, no need to raise the IPI.

  	 * The pairing atomic_fetch_andnot() in irq_work_run() makes sure

  	 * everything we did before is visible.

  	 */

  	if (oflags & IRQ_WORK_PENDING)
  		return false;

  	return true;
  }

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

  /* Enqueue on current CPU, work must already be claimed and preempt disabled */
  static void __irq_work_queue_local(struct irq_work *work)

  {

  	/* If the work is "lazy", handle it from next tick if any */

  	if (atomic_read(&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();
  	}
  }

  /* 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();
  	__irq_work_queue_local(work);
  	preempt_enable();

  	return true;
  }

  EXPORT_SYMBOL_GPL(irq_work_queue);

  /*
   * 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)

  {

  #ifndef CONFIG_SMP
  	return irq_work_queue(work);
  
  #else /* CONFIG_SMP: */
  	/* All work should have been flushed before going offline */
  	WARN_ON_ONCE(cpu_is_offline(cpu));

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

  		return false;

  	preempt_disable();

  	if (cpu != smp_processor_id()) {
  		/* Arch remote IPI send/receive backend aren't NMI safe */
  		WARN_ON_ONCE(in_nmi());

  		__smp_call_single_queue(cpu, &work->llnode);

  	} else {

  		__irq_work_queue_local(work);

  	}

  	preempt_enable();

  
  	return true;

  #endif /* CONFIG_SMP */

  }

  EXPORT_SYMBOL_GPL(irq_work_queue_on);

  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;
  }

  void irq_work_single(void *arg)
  {
  	struct irq_work *work = arg;
  	int flags;
  
  	/*
  	 * 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 = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
  
  	lockdep_irq_work_enter(work);
  	work->func(work);
  	lockdep_irq_work_exit(work);
  	/*
  	 * Clear the BUSY bit and return to the free state if
  	 * no-one else claimed it meanwhile.
  	 */
  	flags &= ~IRQ_WORK_PENDING;
  	(void)atomic_cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
  }

  static void irq_work_run_list(struct llist_head *list)

  {

  	struct irq_work *work, *tmp;

  	struct llist_node *llnode;

  	BUG_ON(!irqs_disabled());

  	if (llist_empty(list))

  		return;

  	llnode = llist_del_all(list);

  	llist_for_each_entry_safe(work, tmp, llnode, llnode)
  		irq_work_single(work);

  }

  
  /*

   * 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)

  {

  	lockdep_assert_irqs_enabled();

  	while (atomic_read(&work->flags) & IRQ_WORK_BUSY)

  		cpu_relax();
  }
  EXPORT_SYMBOL_GPL(irq_work_sync);