kernel/softirq.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *      linux/kernel/softirq.c
   4  *
   5  *      Copyright (C) 1992 Linus Torvalds
   6  *
   7  *      Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
   8  */
   9
  10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  11
  12 #include <linux/export.h>
  13 #include <linux/kernel_stat.h>
  14 #include <linux/interrupt.h>
  15 #include <linux/init.h>
  16 #include <linux/local_lock.h>
  17 #include <linux/mm.h>
  18 #include <linux/notifier.h>
  19 #include <linux/percpu.h>
  20 #include <linux/cpu.h>
  21 #include <linux/freezer.h>
  22 #include <linux/kthread.h>
  23 #include <linux/rcupdate.h>
  24 #include <linux/ftrace.h>
  25 #include <linux/smp.h>
  26 #include <linux/smpboot.h>
  27 #include <linux/tick.h>
  28 #include <linux/irq.h>
  29 #include <linux/wait_bit.h>
  30 #include <linux/workqueue.h>
  31
  32 #include <asm/softirq_stack.h>
  33
  34 #define CREATE_TRACE_POINTS
  35 #include <trace/events/irq.h>
  36
  37 /*
  38    - No shared variables, all the data are CPU local.
  39    - If a softirq needs serialization, let it serialize itself
  40      by its own spinlocks.
  41    - Even if softirq is serialized, only local cpu is marked for
  42      execution. Hence, we get something sort of weak cpu binding.
  43      Though it is still not clear, will it result in better locality
  44      or will not.
  45
  46    Examples:
  47    - NET RX softirq. It is multithreaded and does not require
  48      any global serialization.
  49    - NET TX softirq. It kicks software netdevice queues, hence
  50      it is logically serialized per device, but this serialization
  51      is invisible to common code.
  52    - Tasklets: serialized wrt itself.
  53  */
  54
  55 #ifndef __ARCH_IRQ_STAT
  56 DEFINE_PER_CPU_ALIGNED(irq_cpustat_t, irq_stat);
  57 EXPORT_PER_CPU_SYMBOL(irq_stat);
  58 #endif
  59
  60 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
  61
  62 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
  63
  64 const char * const softirq_to_name[NR_SOFTIRQS] = {
  65         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
  66         "TASKLET", "SCHED", "HRTIMER", "RCU"
  67 };
  68
  69 /*
  70  * we cannot loop indefinitely here to avoid userspace starvation,
  71  * but we also don't want to introduce a worst case 1/HZ latency
  72  * to the pending events, so lets the scheduler to balance
  73  * the softirq load for us.
  74  */
  75 static void wakeup_softirqd(void)
  76 {
  77         /* Interrupts are disabled: no need to stop preemption */
  78         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  79
  80         if (tsk)
  81                 wake_up_process(tsk);
  82 }
  83
  84 #ifdef CONFIG_TRACE_IRQFLAGS
  85 DEFINE_PER_CPU(int, hardirqs_enabled);
  86 DEFINE_PER_CPU(int, hardirq_context);
  87 EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
  88 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
  89 #endif
  90
  91 /*
  92  * SOFTIRQ_OFFSET usage:
  93  *
  94  * On !RT kernels 'count' is the preempt counter, on RT kernels this applies
  95  * to a per CPU counter and to task::softirqs_disabled_cnt.
  96  *
  97  * - count is changed by SOFTIRQ_OFFSET on entering or leaving softirq
  98  *   processing.
  99  *
 100  * - count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
 101  *   on local_bh_disable or local_bh_enable.
 102  *
 103  * This lets us distinguish between whether we are currently processing
 104  * softirq and whether we just have bh disabled.
 105  */
 106 #ifdef CONFIG_PREEMPT_RT
 107
 108 /*
 109  * RT accounts for BH disabled sections in task::softirqs_disabled_cnt and
 110  * also in per CPU softirq_ctrl::cnt. This is necessary to allow tasks in a
 111  * softirq disabled section to be preempted.
 112  *
 113  * The per task counter is used for softirq_count(), in_softirq() and
 114  * in_serving_softirqs() because these counts are only valid when the task
 115  * holding softirq_ctrl::lock is running.
 116  *
 117  * The per CPU counter prevents pointless wakeups of ksoftirqd in case that
 118  * the task which is in a softirq disabled section is preempted or blocks.
 119  */
 120 struct softirq_ctrl {
 121         local_lock_t    lock;
 122         int             cnt;
 123 };
 124
 125 static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl) = {
 126         .lock   = INIT_LOCAL_LOCK(softirq_ctrl.lock),
 127 };
 128
 129 /**
 130  * local_bh_blocked() - Check for idle whether BH processing is blocked
 131  *
 132  * Returns false if the per CPU softirq::cnt is 0 otherwise true.
 133  *
 134  * This is invoked from the idle task to guard against false positive
 135  * softirq pending warnings, which would happen when the task which holds
 136  * softirq_ctrl::lock was the only running task on the CPU and blocks on
 137  * some other lock.
 138  */
 139 bool local_bh_blocked(void)
 140 {
 141         return __this_cpu_read(softirq_ctrl.cnt) != 0;
 142 }
 143
 144 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 145 {
 146         unsigned long flags;
 147         int newcnt;
 148
 149         WARN_ON_ONCE(in_hardirq());
 150
 151         /* First entry of a task into a BH disabled section? */
 152         if (!current->softirq_disable_cnt) {
 153                 if (preemptible()) {
 154                         local_lock(&softirq_ctrl.lock);
 155                         /* Required to meet the RCU bottomhalf requirements. */
 156                         rcu_read_lock();
 157                 } else {
 158                         DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt));
 159                 }
 160         }
 161
 162         /*
 163          * Track the per CPU softirq disabled state. On RT this is per CPU
 164          * state to allow preemption of bottom half disabled sections.
 165          */
 166         newcnt = __this_cpu_add_return(softirq_ctrl.cnt, cnt);
 167         /*
 168          * Reflect the result in the task state to prevent recursion on the
 169          * local lock and to make softirq_count() & al work.
 170          */
 171         current->softirq_disable_cnt = newcnt;
 172
 173         if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) {
 174                 raw_local_irq_save(flags);
 175                 lockdep_softirqs_off(ip);
 176                 raw_local_irq_restore(flags);
 177         }
 178 }
 179 EXPORT_SYMBOL(__local_bh_disable_ip);
 180
 181 static void __local_bh_enable(unsigned int cnt, bool unlock)
 182 {
 183         unsigned long flags;
 184         int newcnt;
 185
 186         DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=
 187                             this_cpu_read(softirq_ctrl.cnt));
 188
 189         if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() == cnt) {
 190                 raw_local_irq_save(flags);
 191                 lockdep_softirqs_on(_RET_IP_);
 192                 raw_local_irq_restore(flags);
 193         }
 194
 195         newcnt = __this_cpu_sub_return(softirq_ctrl.cnt, cnt);
 196         current->softirq_disable_cnt = newcnt;
 197
 198         if (!newcnt && unlock) {
 199                 rcu_read_unlock();
 200                 local_unlock(&softirq_ctrl.lock);
 201         }
 202 }
 203
 204 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 205 {
 206         bool preempt_on = preemptible();
 207         unsigned long flags;
 208         u32 pending;
 209         int curcnt;
 210
 211         WARN_ON_ONCE(in_hardirq());
 212         lockdep_assert_irqs_enabled();
 213
 214         local_irq_save(flags);
 215         curcnt = __this_cpu_read(softirq_ctrl.cnt);
 216
 217         /*
 218          * If this is not reenabling soft interrupts, no point in trying to
 219          * run pending ones.
 220          */
 221         if (curcnt != cnt)
 222                 goto out;
 223
 224         pending = local_softirq_pending();
 225         if (!pending)
 226                 goto out;
 227
 228         /*
 229          * If this was called from non preemptible context, wake up the
 230          * softirq daemon.
 231          */
 232         if (!preempt_on) {
 233                 wakeup_softirqd();
 234                 goto out;
 235         }
 236
 237         /*
 238          * Adjust softirq count to SOFTIRQ_OFFSET which makes
 239          * in_serving_softirq() become true.
 240          */
 241         cnt = SOFTIRQ_OFFSET;
 242         __local_bh_enable(cnt, false);
 243         __do_softirq();
 244
 245 out:
 246         __local_bh_enable(cnt, preempt_on);
 247         local_irq_restore(flags);
 248 }
 249 EXPORT_SYMBOL(__local_bh_enable_ip);
 250
 251 /*
 252  * Invoked from ksoftirqd_run() outside of the interrupt disabled section
 253  * to acquire the per CPU local lock for reentrancy protection.
 254  */
 255 static inline void ksoftirqd_run_begin(void)
 256 {
 257         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 258         local_irq_disable();
 259 }
 260
 261 /* Counterpart to ksoftirqd_run_begin() */
 262 static inline void ksoftirqd_run_end(void)
 263 {
 264         __local_bh_enable(SOFTIRQ_OFFSET, true);
 265         WARN_ON_ONCE(in_interrupt());
 266         local_irq_enable();
 267 }
 268
 269 static inline void softirq_handle_begin(void) { }
 270 static inline void softirq_handle_end(void) { }
 271
 272 static inline bool should_wake_ksoftirqd(void)
 273 {
 274         return !this_cpu_read(softirq_ctrl.cnt);
 275 }
 276
 277 static inline void invoke_softirq(void)
 278 {
 279         if (should_wake_ksoftirqd())
 280                 wakeup_softirqd();
 281 }
 282
 283 /*
 284  * flush_smp_call_function_queue() can raise a soft interrupt in a function
 285  * call. On RT kernels this is undesired and the only known functionality
 286  * in the block layer which does this is disabled on RT. If soft interrupts
 287  * get raised which haven't been raised before the flush, warn so it can be
 288  * investigated.
 289  */
 290 void do_softirq_post_smp_call_flush(unsigned int was_pending)
 291 {
 292         if (WARN_ON_ONCE(was_pending != local_softirq_pending()))
 293                 invoke_softirq();
 294 }
 295
 296 #else /* CONFIG_PREEMPT_RT */
 297
 298 /*
 299  * This one is for softirq.c-internal use, where hardirqs are disabled
 300  * legitimately:
 301  */
 302 #ifdef CONFIG_TRACE_IRQFLAGS
 303 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 304 {
 305         unsigned long flags;
 306
 307         WARN_ON_ONCE(in_hardirq());
 308
 309         raw_local_irq_save(flags);
 310         /*
 311          * The preempt tracer hooks into preempt_count_add and will break
 312          * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 313          * is set and before current->softirq_enabled is cleared.
 314          * We must manually increment preempt_count here and manually
 315          * call the trace_preempt_off later.
 316          */
 317         __preempt_count_add(cnt);
 318         /*
 319          * Were softirqs turned off above:
 320          */
 321         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 322                 lockdep_softirqs_off(ip);
 323         raw_local_irq_restore(flags);
 324
 325         if (preempt_count() == cnt) {
 326 #ifdef CONFIG_DEBUG_PREEMPT
 327                 current->preempt_disable_ip = get_lock_parent_ip();
 328 #endif
 329                 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
 330         }
 331 }
 332 EXPORT_SYMBOL(__local_bh_disable_ip);
 333 #endif /* CONFIG_TRACE_IRQFLAGS */
 334
 335 static void __local_bh_enable(unsigned int cnt)
 336 {
 337         lockdep_assert_irqs_disabled();
 338
 339         if (preempt_count() == cnt)
 340                 trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 341
 342         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 343                 lockdep_softirqs_on(_RET_IP_);
 344
 345         __preempt_count_sub(cnt);
 346 }
 347
 348 /*
 349  * Special-case - softirqs can safely be enabled by __do_softirq(),
 350  * without processing still-pending softirqs:
 351  */
 352 void _local_bh_enable(void)
 353 {
 354         WARN_ON_ONCE(in_hardirq());
 355         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 356 }
 357 EXPORT_SYMBOL(_local_bh_enable);
 358
 359 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 360 {
 361         WARN_ON_ONCE(in_hardirq());
 362         lockdep_assert_irqs_enabled();
 363 #ifdef CONFIG_TRACE_IRQFLAGS
 364         local_irq_disable();
 365 #endif
 366         /*
 367          * Are softirqs going to be turned on now:
 368          */
 369         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 370                 lockdep_softirqs_on(ip);
 371         /*
 372          * Keep preemption disabled until we are done with
 373          * softirq processing:
 374          */
 375         __preempt_count_sub(cnt - 1);
 376
 377         if (unlikely(!in_interrupt() && local_softirq_pending())) {
 378                 /*
 379                  * Run softirq if any pending. And do it in its own stack
 380                  * as we may be calling this deep in a task call stack already.
 381                  */
 382                 do_softirq();
 383         }
 384
 385         preempt_count_dec();
 386 #ifdef CONFIG_TRACE_IRQFLAGS
 387         local_irq_enable();
 388 #endif
 389         preempt_check_resched();
 390 }
 391 EXPORT_SYMBOL(__local_bh_enable_ip);
 392
 393 static inline void softirq_handle_begin(void)
 394 {
 395         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 396 }
 397
 398 static inline void softirq_handle_end(void)
 399 {
 400         __local_bh_enable(SOFTIRQ_OFFSET);
 401         WARN_ON_ONCE(in_interrupt());
 402 }
 403
 404 static inline void ksoftirqd_run_begin(void)
 405 {
 406         local_irq_disable();
 407 }
 408
 409 static inline void ksoftirqd_run_end(void)
 410 {
 411         local_irq_enable();
 412 }
 413
 414 static inline bool should_wake_ksoftirqd(void)
 415 {
 416         return true;
 417 }
 418
 419 static inline void invoke_softirq(void)
 420 {
 421         if (!force_irqthreads() || !__this_cpu_read(ksoftirqd)) {
 422 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 423                 /*
 424                  * We can safely execute softirq on the current stack if
 425                  * it is the irq stack, because it should be near empty
 426                  * at this stage.
 427                  */
 428                 __do_softirq();
 429 #else
 430                 /*
 431                  * Otherwise, irq_exit() is called on the task stack that can
 432                  * be potentially deep already. So call softirq in its own stack
 433                  * to prevent from any overrun.
 434                  */
 435                 do_softirq_own_stack();
 436 #endif
 437         } else {
 438                 wakeup_softirqd();
 439         }
 440 }
 441
 442 asmlinkage __visible void do_softirq(void)
 443 {
 444         __u32 pending;
 445         unsigned long flags;
 446
 447         if (in_interrupt())
 448                 return;
 449
 450         local_irq_save(flags);
 451
 452         pending = local_softirq_pending();
 453
 454         if (pending)
 455                 do_softirq_own_stack();
 456
 457         local_irq_restore(flags);
 458 }
 459
 460 #endif /* !CONFIG_PREEMPT_RT */
 461
 462 /*
 463  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 464  * but break the loop if need_resched() is set or after 2 ms.
 465  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 466  * certain cases, such as stop_machine(), jiffies may cease to
 467  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 468  * well to make sure we eventually return from this method.
 469  *
 470  * These limits have been established via experimentation.
 471  * The two things to balance is latency against fairness -
 472  * we want to handle softirqs as soon as possible, but they
 473  * should not be able to lock up the box.
 474  */
 475 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 476 #define MAX_SOFTIRQ_RESTART 10
 477
 478 #ifdef CONFIG_TRACE_IRQFLAGS
 479 /*
 480  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 481  * to keep the lockdep irq context tracking as tight as possible in order to
 482  * not miss-qualify lock contexts and miss possible deadlocks.
 483  */
 484
 485 static inline bool lockdep_softirq_start(void)
 486 {
 487         bool in_hardirq = false;
 488
 489         if (lockdep_hardirq_context()) {
 490                 in_hardirq = true;
 491                 lockdep_hardirq_exit();
 492         }
 493
 494         lockdep_softirq_enter();
 495
 496         return in_hardirq;
 497 }
 498
 499 static inline void lockdep_softirq_end(bool in_hardirq)
 500 {
 501         lockdep_softirq_exit();
 502
 503         if (in_hardirq)
 504                 lockdep_hardirq_enter();
 505 }
 506 #else
 507 static inline bool lockdep_softirq_start(void) { return false; }
 508 static inline void lockdep_softirq_end(bool in_hardirq) { }
 509 #endif
 510
 511 asmlinkage __visible void __softirq_entry __do_softirq(void)
 512 {
 513         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 514         unsigned long old_flags = current->flags;
 515         int max_restart = MAX_SOFTIRQ_RESTART;
 516         struct softirq_action *h;
 517         bool in_hardirq;
 518         __u32 pending;
 519         int softirq_bit;
 520
 521         /*
 522          * Mask out PF_MEMALLOC as the current task context is borrowed for the
 523          * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
 524          * again if the socket is related to swapping.
 525          */
 526         current->flags &= ~PF_MEMALLOC;
 527
 528         pending = local_softirq_pending();
 529
 530         softirq_handle_begin();
 531         in_hardirq = lockdep_softirq_start();
 532         account_softirq_enter(current);
 533
 534 restart:
 535         /* Reset the pending bitmask before enabling irqs */
 536         set_softirq_pending(0);
 537
 538         local_irq_enable();
 539
 540         h = softirq_vec;
 541
 542         while ((softirq_bit = ffs(pending))) {
 543                 unsigned int vec_nr;
 544                 int prev_count;
 545
 546                 h += softirq_bit - 1;
 547
 548                 vec_nr = h - softirq_vec;
 549                 prev_count = preempt_count();
 550
 551                 kstat_incr_softirqs_this_cpu(vec_nr);
 552
 553                 trace_softirq_entry(vec_nr);
 554                 h->action(h);
 555                 trace_softirq_exit(vec_nr);
 556                 if (unlikely(prev_count != preempt_count())) {
 557                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 558                                vec_nr, softirq_to_name[vec_nr], h->action,
 559                                prev_count, preempt_count());
 560                         preempt_count_set(prev_count);
 561                 }
 562                 h++;
 563                 pending >>= softirq_bit;
 564         }
 565
 566         if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
 567             __this_cpu_read(ksoftirqd) == current)
 568                 rcu_softirq_qs();
 569
 570         local_irq_disable();
 571
 572         pending = local_softirq_pending();
 573         if (pending) {
 574                 if (time_before(jiffies, end) && !need_resched() &&
 575                     --max_restart)
 576                         goto restart;
 577
 578                 wakeup_softirqd();
 579         }
 580
 581         account_softirq_exit(current);
 582         lockdep_softirq_end(in_hardirq);
 583         softirq_handle_end();
 584         current_restore_flags(old_flags, PF_MEMALLOC);
 585 }
 586
 587 /**
 588  * irq_enter_rcu - Enter an interrupt context with RCU watching
 589  */
 590 void irq_enter_rcu(void)
 591 {
 592         __irq_enter_raw();
 593
 594         if (tick_nohz_full_cpu(smp_processor_id()) ||
 595             (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET)))
 596                 tick_irq_enter();
 597
 598         account_hardirq_enter(current);
 599 }
 600
 601 /**
 602  * irq_enter - Enter an interrupt context including RCU update
 603  */
 604 void irq_enter(void)
 605 {
 606         ct_irq_enter();
 607         irq_enter_rcu();
 608 }
 609
 610 static inline void tick_irq_exit(void)
 611 {
 612 #ifdef CONFIG_NO_HZ_COMMON
 613         int cpu = smp_processor_id();
 614
 615         /* Make sure that timer wheel updates are propagated */
 616         if ((sched_core_idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 617                 if (!in_hardirq())
 618                         tick_nohz_irq_exit();
 619         }
 620 #endif
 621 }
 622
 623 static inline void __irq_exit_rcu(void)
 624 {
 625 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 626         local_irq_disable();
 627 #else
 628         lockdep_assert_irqs_disabled();
 629 #endif
 630         account_hardirq_exit(current);
 631         preempt_count_sub(HARDIRQ_OFFSET);
 632         if (!in_interrupt() && local_softirq_pending())
 633                 invoke_softirq();
 634
 635         tick_irq_exit();
 636 }
 637
 638 /**
 639  * irq_exit_rcu() - Exit an interrupt context without updating RCU
 640  *
 641  * Also processes softirqs if needed and possible.
 642  */
 643 void irq_exit_rcu(void)
 644 {
 645         __irq_exit_rcu();
 646          /* must be last! */
 647         lockdep_hardirq_exit();
 648 }
 649
 650 /**
 651  * irq_exit - Exit an interrupt context, update RCU and lockdep
 652  *
 653  * Also processes softirqs if needed and possible.
 654  */
 655 void irq_exit(void)
 656 {
 657         __irq_exit_rcu();
 658         ct_irq_exit();
 659          /* must be last! */
 660         lockdep_hardirq_exit();
 661 }
 662
 663 /*
 664  * This function must run with irqs disabled!
 665  */
 666 inline void raise_softirq_irqoff(unsigned int nr)
 667 {
 668         __raise_softirq_irqoff(nr);
 669
 670         /*
 671          * If we're in an interrupt or softirq, we're done
 672          * (this also catches softirq-disabled code). We will
 673          * actually run the softirq once we return from
 674          * the irq or softirq.
 675          *
 676          * Otherwise we wake up ksoftirqd to make sure we
 677          * schedule the softirq soon.
 678          */
 679         if (!in_interrupt() && should_wake_ksoftirqd())
 680                 wakeup_softirqd();
 681 }
 682
 683 void raise_softirq(unsigned int nr)
 684 {
 685         unsigned long flags;
 686
 687         local_irq_save(flags);
 688         raise_softirq_irqoff(nr);
 689         local_irq_restore(flags);
 690 }
 691
 692 void __raise_softirq_irqoff(unsigned int nr)
 693 {
 694         lockdep_assert_irqs_disabled();
 695         trace_softirq_raise(nr);
 696         or_softirq_pending(1UL << nr);
 697 }
 698
 699 void open_softirq(int nr, void (*action)(struct softirq_action *))
 700 {
 701         softirq_vec[nr].action = action;
 702 }
 703
 704 /*
 705  * Tasklets
 706  */
 707 struct tasklet_head {
 708         struct tasklet_struct *head;
 709         struct tasklet_struct **tail;
 710 };
 711
 712 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 713 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 714
 715 static void __tasklet_schedule_common(struct tasklet_struct *t,
 716                                       struct tasklet_head __percpu *headp,
 717                                       unsigned int softirq_nr)
 718 {
 719         struct tasklet_head *head;
 720         unsigned long flags;
 721
 722         local_irq_save(flags);
 723         head = this_cpu_ptr(headp);
 724         t->next = NULL;
 725         *head->tail = t;
 726         head->tail = &(t->next);
 727         raise_softirq_irqoff(softirq_nr);
 728         local_irq_restore(flags);
 729 }
 730
 731 void __tasklet_schedule(struct tasklet_struct *t)
 732 {
 733         __tasklet_schedule_common(t, &tasklet_vec,
 734                                   TASKLET_SOFTIRQ);
 735 }
 736 EXPORT_SYMBOL(__tasklet_schedule);
 737
 738 void __tasklet_hi_schedule(struct tasklet_struct *t)
 739 {
 740         __tasklet_schedule_common(t, &tasklet_hi_vec,
 741                                   HI_SOFTIRQ);
 742 }
 743 EXPORT_SYMBOL(__tasklet_hi_schedule);
 744
 745 static bool tasklet_clear_sched(struct tasklet_struct *t)
 746 {
 747         if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
 748                 wake_up_var(&t->state);
 749                 return true;
 750         }
 751
 752         WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
 753                   t->use_callback ? "callback" : "func",
 754                   t->use_callback ? (void *)t->callback : (void *)t->func);
 755
 756         return false;
 757 }
 758
 759 static void tasklet_action_common(struct softirq_action *a,
 760                                   struct tasklet_head *tl_head,
 761                                   unsigned int softirq_nr)
 762 {
 763         struct tasklet_struct *list;
 764
 765         local_irq_disable();
 766         list = tl_head->head;
 767         tl_head->head = NULL;
 768         tl_head->tail = &tl_head->head;
 769         local_irq_enable();
 770
 771         while (list) {
 772                 struct tasklet_struct *t = list;
 773
 774                 list = list->next;
 775
 776                 if (tasklet_trylock(t)) {
 777                         if (!atomic_read(&t->count)) {
 778                                 if (tasklet_clear_sched(t)) {
 779                                         if (t->use_callback) {
 780                                                 trace_tasklet_entry(t, t->callback);
 781                                                 t->callback(t);
 782                                                 trace_tasklet_exit(t, t->callback);
 783                                         } else {
 784                                                 trace_tasklet_entry(t, t->func);
 785                                                 t->func(t->data);
 786                                                 trace_tasklet_exit(t, t->func);
 787                                         }
 788                                 }
 789                                 tasklet_unlock(t);
 790                                 continue;
 791                         }
 792                         tasklet_unlock(t);
 793                 }
 794
 795                 local_irq_disable();
 796                 t->next = NULL;
 797                 *tl_head->tail = t;
 798                 tl_head->tail = &t->next;
 799                 __raise_softirq_irqoff(softirq_nr);
 800                 local_irq_enable();
 801         }
 802 }
 803
 804 static __latent_entropy void tasklet_action(struct softirq_action *a)
 805 {
 806         workqueue_softirq_action(false);
 807         tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
 808 }
 809
 810 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
 811 {
 812         workqueue_softirq_action(true);
 813         tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
 814 }
 815
 816 void tasklet_setup(struct tasklet_struct *t,
 817                    void (*callback)(struct tasklet_struct *))
 818 {
 819         t->next = NULL;
 820         t->state = 0;
 821         atomic_set(&t->count, 0);
 822         t->callback = callback;
 823         t->use_callback = true;
 824         t->data = 0;
 825 }
 826 EXPORT_SYMBOL(tasklet_setup);
 827
 828 void tasklet_init(struct tasklet_struct *t,
 829                   void (*func)(unsigned long), unsigned long data)
 830 {
 831         t->next = NULL;
 832         t->state = 0;
 833         atomic_set(&t->count, 0);
 834         t->func = func;
 835         t->use_callback = false;
 836         t->data = data;
 837 }
 838 EXPORT_SYMBOL(tasklet_init);
 839
 840 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 841 /*
 842  * Do not use in new code. Waiting for tasklets from atomic contexts is
 843  * error prone and should be avoided.
 844  */
 845 void tasklet_unlock_spin_wait(struct tasklet_struct *t)
 846 {
 847         while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
 848                 if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 849                         /*
 850                          * Prevent a live lock when current preempted soft
 851                          * interrupt processing or prevents ksoftirqd from
 852                          * running. If the tasklet runs on a different CPU
 853                          * then this has no effect other than doing the BH
 854                          * disable/enable dance for nothing.
 855                          */
 856                         local_bh_disable();
 857                         local_bh_enable();
 858                 } else {
 859                         cpu_relax();
 860                 }
 861         }
 862 }
 863 EXPORT_SYMBOL(tasklet_unlock_spin_wait);
 864 #endif
 865
 866 void tasklet_kill(struct tasklet_struct *t)
 867 {
 868         if (in_interrupt())
 869                 pr_notice("Attempt to kill tasklet from interrupt\n");
 870
 871         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
 872                 wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
 873
 874         tasklet_unlock_wait(t);
 875         tasklet_clear_sched(t);
 876 }
 877 EXPORT_SYMBOL(tasklet_kill);
 878
 879 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 880 void tasklet_unlock(struct tasklet_struct *t)
 881 {
 882         smp_mb__before_atomic();
 883         clear_bit(TASKLET_STATE_RUN, &t->state);
 884         smp_mb__after_atomic();
 885         wake_up_var(&t->state);
 886 }
 887 EXPORT_SYMBOL_GPL(tasklet_unlock);
 888
 889 void tasklet_unlock_wait(struct tasklet_struct *t)
 890 {
 891         wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));
 892 }
 893 EXPORT_SYMBOL_GPL(tasklet_unlock_wait);
 894 #endif
 895
 896 void __init softirq_init(void)
 897 {
 898         int cpu;
 899
 900         for_each_possible_cpu(cpu) {
 901                 per_cpu(tasklet_vec, cpu).tail =
 902                         &per_cpu(tasklet_vec, cpu).head;
 903                 per_cpu(tasklet_hi_vec, cpu).tail =
 904                         &per_cpu(tasklet_hi_vec, cpu).head;
 905         }
 906
 907         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 908         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 909 }
 910
 911 static int ksoftirqd_should_run(unsigned int cpu)
 912 {
 913         return local_softirq_pending();
 914 }
 915
 916 static void run_ksoftirqd(unsigned int cpu)
 917 {
 918         ksoftirqd_run_begin();
 919         if (local_softirq_pending()) {
 920                 /*
 921                  * We can safely run softirq on inline stack, as we are not deep
 922                  * in the task stack here.
 923                  */
 924                 __do_softirq();
 925                 ksoftirqd_run_end();
 926                 cond_resched();
 927                 return;
 928         }
 929         ksoftirqd_run_end();
 930 }
 931
 932 #ifdef CONFIG_HOTPLUG_CPU
 933 static int takeover_tasklets(unsigned int cpu)
 934 {
 935         workqueue_softirq_dead(cpu);
 936
 937         /* CPU is dead, so no lock needed. */
 938         local_irq_disable();
 939
 940         /* Find end, append list for that CPU. */
 941         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 942                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 943                 __this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 944                 per_cpu(tasklet_vec, cpu).head = NULL;
 945                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 946         }
 947         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 948
 949         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 950                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 951                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 952                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 953                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 954         }
 955         raise_softirq_irqoff(HI_SOFTIRQ);
 956
 957         local_irq_enable();
 958         return 0;
 959 }
 960 #else
 961 #define takeover_tasklets       NULL
 962 #endif /* CONFIG_HOTPLUG_CPU */
 963
 964 static struct smp_hotplug_thread softirq_threads = {
 965         .store                  = &ksoftirqd,
 966         .thread_should_run      = ksoftirqd_should_run,
 967         .thread_fn              = run_ksoftirqd,
 968         .thread_comm            = "ksoftirqd/%u",
 969 };
 970
 971 static __init int spawn_ksoftirqd(void)
 972 {
 973         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
 974                                   takeover_tasklets);
 975         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 976
 977         return 0;
 978 }
 979 early_initcall(spawn_ksoftirqd);
 980
 981 /*
 982  * [ These __weak aliases are kept in a separate compilation unit, so that
 983  *   GCC does not inline them incorrectly. ]
 984  */
 985
 986 int __init __weak early_irq_init(void)
 987 {
 988         return 0;
 989 }
 990
 991 int __init __weak arch_probe_nr_irqs(void)
 992 {
 993         return NR_IRQS_LEGACY;
 994 }
 995
 996 int __init __weak arch_early_irq_init(void)
 997 {
 998         return 0;
 999 }
1000
1001 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
1002 {
1003         return from;
1004 }