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