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_CLAIMED; 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 /* 60 * Enqueue the irq_work @work on @cpu unless it's already pending 61 * somewhere. 62 * 63 * Can be re-enqueued while the callback is still in progress. 64 */ 65 bool irq_work_queue_on(struct irq_work *work, int cpu) 66 { 67 /* All work should have been flushed before going offline */ 68 WARN_ON_ONCE(cpu_is_offline(cpu)); 69 70 #ifdef CONFIG_SMP 71 72 /* Arch remote IPI send/receive backend aren't NMI safe */ 73 WARN_ON_ONCE(in_nmi()); 74 75 /* Only queue if not already pending */ 76 if (!irq_work_claim(work)) 77 return false; 78 79 if (llist_add(&work->llnode, &per_cpu(raised_list, cpu))) 80 arch_send_call_function_single_ipi(cpu); 81 82 #else /* #ifdef CONFIG_SMP */ 83 irq_work_queue(work); 84 #endif /* #else #ifdef CONFIG_SMP */ 85 86 return true; 87 } 88 89 /* Enqueue the irq work @work on the current CPU */ 90 bool irq_work_queue(struct irq_work *work) 91 { 92 /* Only queue if not already pending */ 93 if (!irq_work_claim(work)) 94 return false; 95 96 /* Queue the entry and raise the IPI if needed. */ 97 preempt_disable(); 98 99 /* If the work is "lazy", handle it from next tick if any */ 100 if (work->flags & IRQ_WORK_LAZY) { 101 if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) && 102 tick_nohz_tick_stopped()) 103 arch_irq_work_raise(); 104 } else { 105 if (llist_add(&work->llnode, this_cpu_ptr(&raised_list))) 106 arch_irq_work_raise(); 107 } 108 109 preempt_enable(); 110 111 return true; 112 } 113 EXPORT_SYMBOL_GPL(irq_work_queue); 114 115 bool irq_work_needs_cpu(void) 116 { 117 struct llist_head *raised, *lazy; 118 119 raised = this_cpu_ptr(&raised_list); 120 lazy = this_cpu_ptr(&lazy_list); 121 122 if (llist_empty(raised) || arch_irq_work_has_interrupt()) 123 if (llist_empty(lazy)) 124 return false; 125 126 /* All work should have been flushed before going offline */ 127 WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); 128 129 return true; 130 } 131 132 static void irq_work_run_list(struct llist_head *list) 133 { 134 struct irq_work *work, *tmp; 135 struct llist_node *llnode; 136 unsigned long flags; 137 138 BUG_ON(!irqs_disabled()); 139 140 if (llist_empty(list)) 141 return; 142 143 llnode = llist_del_all(list); 144 llist_for_each_entry_safe(work, tmp, llnode, llnode) { 145 /* 146 * Clear the PENDING bit, after this point the @work 147 * can be re-used. 148 * Make it immediately visible so that other CPUs trying 149 * to claim that work don't rely on us to handle their data 150 * while we are in the middle of the func. 151 */ 152 flags = work->flags & ~IRQ_WORK_PENDING; 153 xchg(&work->flags, flags); 154 155 work->func(work); 156 /* 157 * Clear the BUSY bit and return to the free state if 158 * no-one else claimed it meanwhile. 159 */ 160 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY); 161 } 162 } 163 164 /* 165 * hotplug calls this through: 166 * hotplug_cfd() -> flush_smp_call_function_queue() 167 */ 168 void irq_work_run(void) 169 { 170 irq_work_run_list(this_cpu_ptr(&raised_list)); 171 irq_work_run_list(this_cpu_ptr(&lazy_list)); 172 } 173 EXPORT_SYMBOL_GPL(irq_work_run); 174 175 void irq_work_tick(void) 176 { 177 struct llist_head *raised = this_cpu_ptr(&raised_list); 178 179 if (!llist_empty(raised) && !arch_irq_work_has_interrupt()) 180 irq_work_run_list(raised); 181 irq_work_run_list(this_cpu_ptr(&lazy_list)); 182 } 183 184 /* 185 * Synchronize against the irq_work @entry, ensures the entry is not 186 * currently in use. 187 */ 188 void irq_work_sync(struct irq_work *work) 189 { 190 lockdep_assert_irqs_enabled(); 191 192 while (work->flags & IRQ_WORK_BUSY) 193 cpu_relax(); 194 } 195 EXPORT_SYMBOL_GPL(irq_work_sync); 196