kernel/irq_work.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
   4  *
   5  * Provides a framework for enqueueing and running callbacks from hardirq
   6  * context. The enqueueing is NMI-safe.
   7  */
   8
   9 #include <linux/bug.h>
  10 #include <linux/kernel.h>
  11 #include <linux/export.h>
  12 #include <linux/irq_work.h>
  13 #include <linux/percpu.h>
  14 #include <linux/hardirq.h>
  15 #include <linux/irqflags.h>
  16 #include <linux/sched.h>
  17 #include <linux/tick.h>
  18 #include <linux/cpu.h>
  19 #include <linux/notifier.h>
  20 #include <linux/smp.h>
  21 #include <linux/smpboot.h>
  22 #include <asm/processor.h>
  23 #include <linux/kasan.h>
  24
  25 static DEFINE_PER_CPU(struct llist_head, raised_list);
  26 static DEFINE_PER_CPU(struct llist_head, lazy_list);
  27 static DEFINE_PER_CPU(struct task_struct *, irq_workd);
  28
  29 static void wake_irq_workd(void)
  30 {
  31         struct task_struct *tsk = __this_cpu_read(irq_workd);
  32
  33         if (!llist_empty(this_cpu_ptr(&lazy_list)) && tsk)
  34                 wake_up_process(tsk);
  35 }
  36
  37 #ifdef CONFIG_SMP
  38 static void irq_work_wake(struct irq_work *entry)
  39 {
  40         wake_irq_workd();
  41 }
  42
  43 static DEFINE_PER_CPU(struct irq_work, irq_work_wakeup) =
  44         IRQ_WORK_INIT_HARD(irq_work_wake);
  45 #endif
  46
  47 static int irq_workd_should_run(unsigned int cpu)
  48 {
  49         return !llist_empty(this_cpu_ptr(&lazy_list));
  50 }
  51
  52 /*
  53  * Claim the entry so that no one else will poke at it.
  54  */
  55 static bool irq_work_claim(struct irq_work *work)
  56 {
  57         int oflags;
  58
  59         oflags = atomic_fetch_or(IRQ_WORK_CLAIMED | CSD_TYPE_IRQ_WORK, &work->node.a_flags);
  60         /*
  61          * If the work is already pending, no need to raise the IPI.
  62          * The pairing smp_mb() in irq_work_single() makes sure
  63          * everything we did before is visible.
  64          */
  65         if (oflags & IRQ_WORK_PENDING)
  66                 return false;
  67         return true;
  68 }
  69
  70 void __weak arch_irq_work_raise(void)
  71 {
  72         /*
  73          * Lame architectures will get the timer tick callback
  74          */
  75 }
  76
  77 /* Enqueue on current CPU, work must already be claimed and preempt disabled */
  78 static void __irq_work_queue_local(struct irq_work *work)
  79 {
  80         struct llist_head *list;
  81         bool rt_lazy_work = false;
  82         bool lazy_work = false;
  83         int work_flags;
  84
  85         work_flags = atomic_read(&work->node.a_flags);
  86         if (work_flags & IRQ_WORK_LAZY)
  87                 lazy_work = true;
  88         else if (IS_ENABLED(CONFIG_PREEMPT_RT) &&
  89                  !(work_flags & IRQ_WORK_HARD_IRQ))
  90                 rt_lazy_work = true;
  91
  92         if (lazy_work || rt_lazy_work)
  93                 list = this_cpu_ptr(&lazy_list);
  94         else
  95                 list = this_cpu_ptr(&raised_list);
  96
  97         if (!llist_add(&work->node.llist, list))
  98                 return;
  99
 100         /* If the work is "lazy", handle it from next tick if any */
 101         if (!lazy_work || tick_nohz_tick_stopped())
 102                 arch_irq_work_raise();
 103 }
 104
 105 /* Enqueue the irq work @work on the current CPU */
 106 bool irq_work_queue(struct irq_work *work)
 107 {
 108         /* Only queue if not already pending */
 109         if (!irq_work_claim(work))
 110                 return false;
 111
 112         /* Queue the entry and raise the IPI if needed. */
 113         preempt_disable();
 114         __irq_work_queue_local(work);
 115         preempt_enable();
 116
 117         return true;
 118 }
 119 EXPORT_SYMBOL_GPL(irq_work_queue);
 120
 121 /*
 122  * Enqueue the irq_work @work on @cpu unless it's already pending
 123  * somewhere.
 124  *
 125  * Can be re-enqueued while the callback is still in progress.
 126  */
 127 bool irq_work_queue_on(struct irq_work *work, int cpu)
 128 {
 129 #ifndef CONFIG_SMP
 130         return irq_work_queue(work);
 131
 132 #else /* CONFIG_SMP: */
 133         /* All work should have been flushed before going offline */
 134         WARN_ON_ONCE(cpu_is_offline(cpu));
 135
 136         /* Only queue if not already pending */
 137         if (!irq_work_claim(work))
 138                 return false;
 139
 140         kasan_record_aux_stack_noalloc(work);
 141
 142         preempt_disable();
 143         if (cpu != smp_processor_id()) {
 144                 /* Arch remote IPI send/receive backend aren't NMI safe */
 145                 WARN_ON_ONCE(in_nmi());
 146
 147                 /*
 148                  * On PREEMPT_RT the items which are not marked as
 149                  * IRQ_WORK_HARD_IRQ are added to the lazy list and a HARD work
 150                  * item is used on the remote CPU to wake the thread.
 151                  */
 152                 if (IS_ENABLED(CONFIG_PREEMPT_RT) &&
 153                     !(atomic_read(&work->node.a_flags) & IRQ_WORK_HARD_IRQ)) {
 154
 155                         if (!llist_add(&work->node.llist, &per_cpu(lazy_list, cpu)))
 156                                 goto out;
 157
 158                         work = &per_cpu(irq_work_wakeup, cpu);
 159                         if (!irq_work_claim(work))
 160                                 goto out;
 161                 }
 162
 163                 __smp_call_single_queue(cpu, &work->node.llist);
 164         } else {
 165                 __irq_work_queue_local(work);
 166         }
 167 out:
 168         preempt_enable();
 169
 170         return true;
 171 #endif /* CONFIG_SMP */
 172 }
 173
 174 bool irq_work_needs_cpu(void)
 175 {
 176         struct llist_head *raised, *lazy;
 177
 178         raised = this_cpu_ptr(&raised_list);
 179         lazy = this_cpu_ptr(&lazy_list);
 180
 181         if (llist_empty(raised) || arch_irq_work_has_interrupt())
 182                 if (llist_empty(lazy))
 183                         return false;
 184
 185         /* All work should have been flushed before going offline */
 186         WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
 187
 188         return true;
 189 }
 190
 191 void irq_work_single(void *arg)
 192 {
 193         struct irq_work *work = arg;
 194         int flags;
 195
 196         /*
 197          * Clear the PENDING bit, after this point the @work can be re-used.
 198          * The PENDING bit acts as a lock, and we own it, so we can clear it
 199          * without atomic ops.
 200          */
 201         flags = atomic_read(&work->node.a_flags);
 202         flags &= ~IRQ_WORK_PENDING;
 203         atomic_set(&work->node.a_flags, flags);
 204
 205         /*
 206          * See irq_work_claim().
 207          */
 208         smp_mb();
 209
 210         lockdep_irq_work_enter(flags);
 211         work->func(work);
 212         lockdep_irq_work_exit(flags);
 213
 214         /*
 215          * Clear the BUSY bit, if set, and return to the free state if no-one
 216          * else claimed it meanwhile.
 217          */
 218         (void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY);
 219
 220         if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
 221             !arch_irq_work_has_interrupt())
 222                 rcuwait_wake_up(&work->irqwait);
 223 }
 224
 225 static void irq_work_run_list(struct llist_head *list)
 226 {
 227         struct irq_work *work, *tmp;
 228         struct llist_node *llnode;
 229
 230         /*
 231          * On PREEMPT_RT IRQ-work which is not marked as HARD will be processed
 232          * in a per-CPU thread in preemptible context. Only the items which are
 233          * marked as IRQ_WORK_HARD_IRQ will be processed in hardirq context.
 234          */
 235         BUG_ON(!irqs_disabled() && !IS_ENABLED(CONFIG_PREEMPT_RT));
 236
 237         if (llist_empty(list))
 238                 return;
 239
 240         llnode = llist_del_all(list);
 241         llist_for_each_entry_safe(work, tmp, llnode, node.llist)
 242                 irq_work_single(work);
 243 }
 244
 245 /*
 246  * hotplug calls this through:
 247  *  hotplug_cfd() -> flush_smp_call_function_queue()
 248  */
 249 void irq_work_run(void)
 250 {
 251         irq_work_run_list(this_cpu_ptr(&raised_list));
 252         if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 253                 irq_work_run_list(this_cpu_ptr(&lazy_list));
 254         else
 255                 wake_irq_workd();
 256 }
 257 EXPORT_SYMBOL_GPL(irq_work_run);
 258
 259 void irq_work_tick(void)
 260 {
 261         struct llist_head *raised = this_cpu_ptr(&raised_list);
 262
 263         if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
 264                 irq_work_run_list(raised);
 265
 266         if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 267                 irq_work_run_list(this_cpu_ptr(&lazy_list));
 268         else
 269                 wake_irq_workd();
 270 }
 271
 272 /*
 273  * Synchronize against the irq_work @entry, ensures the entry is not
 274  * currently in use.
 275  */
 276 void irq_work_sync(struct irq_work *work)
 277 {
 278         lockdep_assert_irqs_enabled();
 279         might_sleep();
 280
 281         if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
 282             !arch_irq_work_has_interrupt()) {
 283                 rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work),
 284                                    TASK_UNINTERRUPTIBLE);
 285                 return;
 286         }
 287
 288         while (irq_work_is_busy(work))
 289                 cpu_relax();
 290 }
 291 EXPORT_SYMBOL_GPL(irq_work_sync);
 292
 293 static void run_irq_workd(unsigned int cpu)
 294 {
 295         irq_work_run_list(this_cpu_ptr(&lazy_list));
 296 }
 297
 298 static void irq_workd_setup(unsigned int cpu)
 299 {
 300         sched_set_fifo_low(current);
 301 }
 302
 303 static struct smp_hotplug_thread irqwork_threads = {
 304         .store                  = &irq_workd,
 305         .setup                  = irq_workd_setup,
 306         .thread_should_run      = irq_workd_should_run,
 307         .thread_fn              = run_irq_workd,
 308         .thread_comm            = "irq_work/%u",
 309 };
 310
 311 static __init int irq_work_init_threads(void)
 312 {
 313         if (IS_ENABLED(CONFIG_PREEMPT_RT))
 314                 BUG_ON(smpboot_register_percpu_thread(&irqwork_threads));
 315         return 0;
 316 }
 317 early_initcall(irq_work_init_threads);