kernel/irq_work.c

   1 /*
   2  * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   3  *
   4  * Provides a framework for enqueueing and running callbacks from hardirq
   5  * context. The enqueueing is NMI-safe.
   6  */
   7
   8 #include <linux/bug.h>
   9 #include <linux/kernel.h>
  10 #include <linux/export.h>
  11 #include <linux/irq_work.h>
  12 #include <linux/percpu.h>
  13 #include <linux/hardirq.h>
  14 #include <asm/processor.h>
  15
  16 /*
  17  * An entry can be in one of four states:
  18  *
  19  * free      NULL, 0 -> {claimed}       : free to be used
  20  * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
  21  * pending   next, 3 -> {busy}          : queued, pending callback
  22  * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
  23  */
  24
  25 #define IRQ_WORK_PENDING        1UL
  26 #define IRQ_WORK_BUSY           2UL
  27 #define IRQ_WORK_FLAGS          3UL
  28
  29 static DEFINE_PER_CPU(struct llist_head, irq_work_list);
  30
  31 /*
  32  * Claim the entry so that no one else will poke at it.
  33  */
  34 static bool irq_work_claim(struct irq_work *work)
  35 {
  36         unsigned long flags, nflags;
  37
  38         for (;;) {
  39                 flags = work->flags;
  40                 if (flags & IRQ_WORK_PENDING)
  41                         return false;
  42                 nflags = flags | IRQ_WORK_FLAGS;
  43                 if (cmpxchg(&work->flags, flags, nflags) == flags)
  44                         break;
  45                 cpu_relax();
  46         }
  47
  48         return true;
  49 }
  50
  51 void __weak arch_irq_work_raise(void)
  52 {
  53         /*
  54          * Lame architectures will get the timer tick callback
  55          */
  56 }
  57
  58 /*
  59  * Queue the entry and raise the IPI if needed.
  60  */
  61 static void __irq_work_queue(struct irq_work *work)
  62 {
  63         bool empty;
  64
  65         preempt_disable();
  66
  67         empty = llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
  68         /* The list was empty, raise self-interrupt to start processing. */
  69         if (empty)
  70                 arch_irq_work_raise();
  71
  72         preempt_enable();
  73 }
  74
  75 /*
  76  * Enqueue the irq_work @entry, returns true on success, failure when the
  77  * @entry was already enqueued by someone else.
  78  *
  79  * Can be re-enqueued while the callback is still in progress.
  80  */
  81 bool irq_work_queue(struct irq_work *work)
  82 {
  83         if (!irq_work_claim(work)) {
  84                 /*
  85                  * Already enqueued, can't do!
  86                  */
  87                 return false;
  88         }
  89
  90         __irq_work_queue(work);
  91         return true;
  92 }
  93 EXPORT_SYMBOL_GPL(irq_work_queue);
  94
  95 /*
  96  * Run the irq_work entries on this cpu. Requires to be ran from hardirq
  97  * context with local IRQs disabled.
  98  */
  99 void irq_work_run(void)
 100 {
 101         struct irq_work *work;
 102         struct llist_head *this_list;
 103         struct llist_node *llnode;
 104
 105         this_list = &__get_cpu_var(irq_work_list);
 106         if (llist_empty(this_list))
 107                 return;
 108
 109         BUG_ON(!in_irq());
 110         BUG_ON(!irqs_disabled());
 111
 112         llnode = llist_del_all(this_list);
 113         while (llnode != NULL) {
 114                 work = llist_entry(llnode, struct irq_work, llnode);
 115
 116                 llnode = llist_next(llnode);
 117
 118                 /*
 119                  * Clear the PENDING bit, after this point the @work
 120                  * can be re-used.
 121                  */
 122                 work->flags = IRQ_WORK_BUSY;
 123                 work->func(work);
 124                 /*
 125                  * Clear the BUSY bit and return to the free state if
 126                  * no-one else claimed it meanwhile.
 127                  */
 128                 (void)cmpxchg(&work->flags, IRQ_WORK_BUSY, 0);
 129         }
 130 }
 131 EXPORT_SYMBOL_GPL(irq_work_run);
 132
 133 /*
 134  * Synchronize against the irq_work @entry, ensures the entry is not
 135  * currently in use.
 136  */
 137 void irq_work_sync(struct irq_work *work)
 138 {
 139         WARN_ON_ONCE(irqs_disabled());
 140
 141         while (work->flags & IRQ_WORK_BUSY)
 142                 cpu_relax();
 143 }
 144 EXPORT_SYMBOL_GPL(irq_work_sync);