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