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Linux/kernel/irq_work.c

  1 /*
  2  * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
  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 <linux/smp.h>
 20 #include <asm/processor.h>
 21 
 22 
 23 static DEFINE_PER_CPU(struct llist_head, raised_list);
 24 static DEFINE_PER_CPU(struct llist_head, lazy_list);
 25 
 26 /*
 27  * Claim the entry so that no one else will poke at it.
 28  */
 29 static bool irq_work_claim(struct irq_work *work)
 30 {
 31         unsigned long flags, oflags, nflags;
 32 
 33         /*
 34          * Start with our best wish as a premise but only trust any
 35          * flag value after cmpxchg() result.
 36          */
 37         flags = work->flags & ~IRQ_WORK_PENDING;
 38         for (;;) {
 39                 nflags = flags | IRQ_WORK_FLAGS;
 40                 oflags = cmpxchg(&work->flags, flags, nflags);
 41                 if (oflags == flags)
 42                         break;
 43                 if (oflags & IRQ_WORK_PENDING)
 44                         return false;
 45                 flags = oflags;
 46                 cpu_relax();
 47         }
 48 
 49         return true;
 50 }
 51 
 52 void __weak arch_irq_work_raise(void)
 53 {
 54         /*
 55          * Lame architectures will get the timer tick callback
 56          */
 57 }
 58 
 59 #ifdef CONFIG_SMP
 60 /*
 61  * Enqueue the irq_work @work on @cpu unless it's already pending
 62  * somewhere.
 63  *
 64  * Can be re-enqueued while the callback is still in progress.
 65  */
 66 bool irq_work_queue_on(struct irq_work *work, int cpu)
 67 {
 68         /* All work should have been flushed before going offline */
 69         WARN_ON_ONCE(cpu_is_offline(cpu));
 70 
 71         /* Arch remote IPI send/receive backend aren't NMI safe */
 72         WARN_ON_ONCE(in_nmi());
 73 
 74         /* Only queue if not already pending */
 75         if (!irq_work_claim(work))
 76                 return false;
 77 
 78         if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
 79                 arch_send_call_function_single_ipi(cpu);
 80 
 81         return true;
 82 }
 83 EXPORT_SYMBOL_GPL(irq_work_queue_on);
 84 #endif
 85 
 86 /* Enqueue the irq work @work on the current CPU */
 87 bool irq_work_queue(struct irq_work *work)
 88 {
 89         /* Only queue if not already pending */
 90         if (!irq_work_claim(work))
 91                 return false;
 92 
 93         /* Queue the entry and raise the IPI if needed. */
 94         preempt_disable();
 95 
 96         /* If the work is "lazy", handle it from next tick if any */
 97         if (work->flags & IRQ_WORK_LAZY) {
 98                 if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
 99                     tick_nohz_tick_stopped())
100                         arch_irq_work_raise();
101         } else {
102                 if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
103                         arch_irq_work_raise();
104         }
105 
106         preempt_enable();
107 
108         return true;
109 }
110 EXPORT_SYMBOL_GPL(irq_work_queue);
111 
112 bool irq_work_needs_cpu(void)
113 {
114         struct llist_head *raised, *lazy;
115 
116         raised = this_cpu_ptr(&raised_list);
117         lazy = this_cpu_ptr(&lazy_list);
118 
119         if (llist_empty(raised) || arch_irq_work_has_interrupt())
120                 if (llist_empty(lazy))
121                         return false;
122 
123         /* All work should have been flushed before going offline */
124         WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
125 
126         return true;
127 }
128 
129 static void irq_work_run_list(struct llist_head *list)
130 {
131         unsigned long flags;
132         struct irq_work *work;
133         struct llist_node *llnode;
134 
135         BUG_ON(!irqs_disabled());
136 
137         if (llist_empty(list))
138                 return;
139 
140         llnode = llist_del_all(list);
141         while (llnode != NULL) {
142                 work = llist_entry(llnode, struct irq_work, llnode);
143 
144                 llnode = llist_next(llnode);
145 
146                 /*
147                  * Clear the PENDING bit, after this point the @work
148                  * can be re-used.
149                  * Make it immediately visible so that other CPUs trying
150                  * to claim that work don't rely on us to handle their data
151                  * while we are in the middle of the func.
152                  */
153                 flags = work->flags & ~IRQ_WORK_PENDING;
154                 xchg(&work->flags, flags);
155 
156                 work->func(work);
157                 /*
158                  * Clear the BUSY bit and return to the free state if
159                  * no-one else claimed it meanwhile.
160                  */
161                 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
162         }
163 }
164 
165 /*
166  * hotplug calls this through:
167  *  hotplug_cfd() -> flush_smp_call_function_queue()
168  */
169 void irq_work_run(void)
170 {
171         irq_work_run_list(this_cpu_ptr(&raised_list));
172         irq_work_run_list(this_cpu_ptr(&lazy_list));
173 }
174 EXPORT_SYMBOL_GPL(irq_work_run);
175 
176 void irq_work_tick(void)
177 {
178         struct llist_head *raised = this_cpu_ptr(&raised_list);
179 
180         if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
181                 irq_work_run_list(raised);
182         irq_work_run_list(this_cpu_ptr(&lazy_list));
183 }
184 
185 /*
186  * Synchronize against the irq_work @entry, ensures the entry is not
187  * currently in use.
188  */
189 void irq_work_sync(struct irq_work *work)
190 {
191         WARN_ON_ONCE(irqs_disabled());
192 
193         while (work->flags & IRQ_WORK_BUSY)
194                 cpu_relax();
195 }
196 EXPORT_SYMBOL_GPL(irq_work_sync);
197 

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