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 /* Enqueue on current CPU, work must already be claimed and preempt disabled */ 60 static void __irq_work_queue_local(struct irq_work *work) 61 { 62 /* If the work is "lazy", handle it from next tick if any */ 63 if (work->flags & IRQ_WORK_LAZY) { 64 if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) && 65 tick_nohz_tick_stopped()) 66 arch_irq_work_raise(); 67 } else { 68 if (llist_add(&work->llnode, this_cpu_ptr(&raised_list))) 69 arch_irq_work_raise(); 70 } 71 } 72 73 /* Enqueue the irq work @work on the current CPU */ 74 bool irq_work_queue(struct irq_work *work) 75 { 76 /* Only queue if not already pending */ 77 if (!irq_work_claim(work)) 78 return false; 79 80 /* Queue the entry and raise the IPI if needed. */ 81 preempt_disable(); 82 __irq_work_queue_local(work); 83 preempt_enable(); 84 85 return true; 86 } 87 EXPORT_SYMBOL_GPL(irq_work_queue); 88 89 /* 90 * Enqueue the irq_work @work on @cpu unless it's already pending 91 * somewhere. 92 * 93 * Can be re-enqueued while the callback is still in progress. 94 */ 95 bool irq_work_queue_on(struct irq_work *work, int cpu) 96 { 97 #ifndef CONFIG_SMP 98 return irq_work_queue(work); 99 100 #else /* CONFIG_SMP: */ 101 /* All work should have been flushed before going offline */ 102 WARN_ON_ONCE(cpu_is_offline(cpu)); 103 104 /* Only queue if not already pending */ 105 if (!irq_work_claim(work)) 106 return false; 107 108 preempt_disable(); 109 if (cpu != smp_processor_id()) { 110 /* Arch remote IPI send/receive backend aren't NMI safe */ 111 WARN_ON_ONCE(in_nmi()); 112 if (llist_add(&work->llnode, &per_cpu(raised_list, cpu))) 113 arch_send_call_function_single_ipi(cpu); 114 } else { 115 __irq_work_queue_local(work); 116 } 117 preempt_enable(); 118 119 return true; 120 #endif /* CONFIG_SMP */ 121 } 122 123 124 bool irq_work_needs_cpu(void) 125 { 126 struct llist_head *raised, *lazy; 127 128 raised = this_cpu_ptr(&raised_list); 129 lazy = this_cpu_ptr(&lazy_list); 130 131 if (llist_empty(raised) || arch_irq_work_has_interrupt()) 132 if (llist_empty(lazy)) 133 return false; 134 135 /* All work should have been flushed before going offline */ 136 WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); 137 138 return true; 139 } 140 141 static void irq_work_run_list(struct llist_head *list) 142 { 143 struct irq_work *work, *tmp; 144 struct llist_node *llnode; 145 unsigned long flags; 146 147 BUG_ON(!irqs_disabled()); 148 149 if (llist_empty(list)) 150 return; 151 152 llnode = llist_del_all(list); 153 llist_for_each_entry_safe(work, tmp, llnode, llnode) { 154 /* 155 * Clear the PENDING bit, after this point the @work 156 * can be re-used. 157 * Make it immediately visible so that other CPUs trying 158 * to claim that work don't rely on us to handle their data 159 * while we are in the middle of the func. 160 */ 161 flags = work->flags & ~IRQ_WORK_PENDING; 162 xchg(&work->flags, flags); 163 164 work->func(work); 165 /* 166 * Clear the BUSY bit and return to the free state if 167 * no-one else claimed it meanwhile. 168 */ 169 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY); 170 } 171 } 172 173 /* 174 * hotplug calls this through: 175 * hotplug_cfd() -> flush_smp_call_function_queue() 176 */ 177 void irq_work_run(void) 178 { 179 irq_work_run_list(this_cpu_ptr(&raised_list)); 180 irq_work_run_list(this_cpu_ptr(&lazy_list)); 181 } 182 EXPORT_SYMBOL_GPL(irq_work_run); 183 184 void irq_work_tick(void) 185 { 186 struct llist_head *raised = this_cpu_ptr(&raised_list); 187 188 if (!llist_empty(raised) && !arch_irq_work_has_interrupt()) 189 irq_work_run_list(raised); 190 irq_work_run_list(this_cpu_ptr(&lazy_list)); 191 } 192 193 /* 194 * Synchronize against the irq_work @entry, ensures the entry is not 195 * currently in use. 196 */ 197 void irq_work_sync(struct irq_work *work) 198 { 199 lockdep_assert_irqs_enabled(); 200 201 while (work->flags & IRQ_WORK_BUSY) 202 cpu_relax(); 203 } 204 EXPORT_SYMBOL_GPL(irq_work_sync); 205