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 <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, &__get_cpu_var(lazy_list)) && 99 tick_nohz_tick_stopped()) 100 arch_irq_work_raise(); 101 } else { 102 if (llist_add(&work->llnode, &__get_cpu_var(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 = &__get_cpu_var(raised_list); 117 lazy = &__get_cpu_var(lazy_list); 118 if (llist_empty(raised) && llist_empty(lazy)) 119 return false; 120 121 /* All work should have been flushed before going offline */ 122 WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); 123 124 return true; 125 } 126 127 static void irq_work_run_list(struct llist_head *list) 128 { 129 unsigned long flags; 130 struct irq_work *work; 131 struct llist_node *llnode; 132 133 BUG_ON(!irqs_disabled()); 134 135 if (llist_empty(list)) 136 return; 137 138 llnode = llist_del_all(list); 139 while (llnode != NULL) { 140 work = llist_entry(llnode, struct irq_work, llnode); 141 142 llnode = llist_next(llnode); 143 144 /* 145 * Clear the PENDING bit, after this point the @work 146 * can be re-used. 147 * Make it immediately visible so that other CPUs trying 148 * to claim that work don't rely on us to handle their data 149 * while we are in the middle of the func. 150 */ 151 flags = work->flags & ~IRQ_WORK_PENDING; 152 xchg(&work->flags, flags); 153 154 work->func(work); 155 /* 156 * Clear the BUSY bit and return to the free state if 157 * no-one else claimed it meanwhile. 158 */ 159 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY); 160 } 161 } 162 163 /* 164 * hotplug calls this through: 165 * hotplug_cfd() -> flush_smp_call_function_queue() 166 */ 167 void irq_work_run(void) 168 { 169 irq_work_run_list(&__get_cpu_var(raised_list)); 170 irq_work_run_list(&__get_cpu_var(lazy_list)); 171 } 172 EXPORT_SYMBOL_GPL(irq_work_run); 173 174 /* 175 * Synchronize against the irq_work @entry, ensures the entry is not 176 * currently in use. 177 */ 178 void irq_work_sync(struct irq_work *work) 179 { 180 WARN_ON_ONCE(irqs_disabled()); 181 182 while (work->flags & IRQ_WORK_BUSY) 183 cpu_relax(); 184 } 185 EXPORT_SYMBOL_GPL(irq_work_sync); 186