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