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Linux/kernel/irq_work.c

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  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 <linux/irqflags.h>
 15 #include <linux/sched.h>
 16 #include <linux/tick.h>
 17 #include <linux/cpu.h>
 18 #include <linux/notifier.h>
 19 #include <asm/processor.h>
 20 
 21 
 22 static DEFINE_PER_CPU(struct llist_head, irq_work_list);
 23 static DEFINE_PER_CPU(int, irq_work_raised);
 24 
 25 /*
 26  * Claim the entry so that no one else will poke at it.
 27  */
 28 static bool irq_work_claim(struct irq_work *work)
 29 {
 30         unsigned long flags, oflags, nflags;
 31 
 32         /*
 33          * Start with our best wish as a premise but only trust any
 34          * flag value after cmpxchg() result.
 35          */
 36         flags = work->flags & ~IRQ_WORK_PENDING;
 37         for (;;) {
 38                 nflags = flags | IRQ_WORK_FLAGS;
 39                 oflags = cmpxchg(&work->flags, flags, nflags);
 40                 if (oflags == flags)
 41                         break;
 42                 if (oflags & IRQ_WORK_PENDING)
 43                         return false;
 44                 flags = oflags;
 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  * Enqueue the irq_work @entry unless it's already pending
 60  * somewhere.
 61  *
 62  * Can be re-enqueued while the callback is still in progress.
 63  */
 64 bool irq_work_queue(struct irq_work *work)
 65 {
 66         /* Only queue if not already pending */
 67         if (!irq_work_claim(work))
 68                 return false;
 69 
 70         /* Queue the entry and raise the IPI if needed. */
 71         preempt_disable();
 72 
 73         llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
 74 
 75         /*
 76          * If the work is not "lazy" or the tick is stopped, raise the irq
 77          * work interrupt (if supported by the arch), otherwise, just wait
 78          * for the next tick.
 79          */
 80         if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) {
 81                 if (!this_cpu_cmpxchg(irq_work_raised, 0, 1))
 82                         arch_irq_work_raise();
 83         }
 84 
 85         preempt_enable();
 86 
 87         return true;
 88 }
 89 EXPORT_SYMBOL_GPL(irq_work_queue);
 90 
 91 bool irq_work_needs_cpu(void)
 92 {
 93         struct llist_head *this_list;
 94 
 95         this_list = &__get_cpu_var(irq_work_list);
 96         if (llist_empty(this_list))
 97                 return false;
 98 
 99         /* All work should have been flushed before going offline */
100         WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
101 
102         return true;
103 }
104 
105 static void __irq_work_run(void)
106 {
107         unsigned long flags;
108         struct irq_work *work;
109         struct llist_head *this_list;
110         struct llist_node *llnode;
111 
112 
113         /*
114          * Reset the "raised" state right before we check the list because
115          * an NMI may enqueue after we find the list empty from the runner.
116          */
117         __this_cpu_write(irq_work_raised, 0);
118         barrier();
119 
120         this_list = &__get_cpu_var(irq_work_list);
121         if (llist_empty(this_list))
122                 return;
123 
124         BUG_ON(!irqs_disabled());
125 
126         llnode = llist_del_all(this_list);
127         while (llnode != NULL) {
128                 work = llist_entry(llnode, struct irq_work, llnode);
129 
130                 llnode = llist_next(llnode);
131 
132                 /*
133                  * Clear the PENDING bit, after this point the @work
134                  * can be re-used.
135                  * Make it immediately visible so that other CPUs trying
136                  * to claim that work don't rely on us to handle their data
137                  * while we are in the middle of the func.
138                  */
139                 flags = work->flags & ~IRQ_WORK_PENDING;
140                 xchg(&work->flags, flags);
141 
142                 work->func(work);
143                 /*
144                  * Clear the BUSY bit and return to the free state if
145                  * no-one else claimed it meanwhile.
146                  */
147                 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
148         }
149 }
150 
151 /*
152  * Run the irq_work entries on this cpu. Requires to be ran from hardirq
153  * context with local IRQs disabled.
154  */
155 void irq_work_run(void)
156 {
157         BUG_ON(!in_irq());
158         __irq_work_run();
159 }
160 EXPORT_SYMBOL_GPL(irq_work_run);
161 
162 /*
163  * Synchronize against the irq_work @entry, ensures the entry is not
164  * currently in use.
165  */
166 void irq_work_sync(struct irq_work *work)
167 {
168         WARN_ON_ONCE(irqs_disabled());
169 
170         while (work->flags & IRQ_WORK_BUSY)
171                 cpu_relax();
172 }
173 EXPORT_SYMBOL_GPL(irq_work_sync);
174 
175 #ifdef CONFIG_HOTPLUG_CPU
176 static int irq_work_cpu_notify(struct notifier_block *self,
177                                unsigned long action, void *hcpu)
178 {
179         long cpu = (long)hcpu;
180 
181         switch (action) {
182         case CPU_DYING:
183                 /* Called from stop_machine */
184                 if (WARN_ON_ONCE(cpu != smp_processor_id()))
185                         break;
186                 __irq_work_run();
187                 break;
188         default:
189                 break;
190         }
191         return NOTIFY_OK;
192 }
193 
194 static struct notifier_block cpu_notify;
195 
196 static __init int irq_work_init_cpu_notifier(void)
197 {
198         cpu_notify.notifier_call = irq_work_cpu_notify;
199         cpu_notify.priority = 0;
200         register_cpu_notifier(&cpu_notify);
201         return 0;
202 }
203 device_initcall(irq_work_init_cpu_notifier);
204 
205 #endif /* CONFIG_HOTPLUG_CPU */
206 

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