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 /*
  84  * If ksoftirqd is scheduled, we do not want to process pending softirqs
  85  * right now. Let ksoftirqd handle this at its own rate, to get fairness,
  86  * unless we're doing some of the synchronous softirqs.
  87  */
  88 #define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ))
  89 static bool ksoftirqd_running(unsigned long pending)
  90 {
  91         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
  92
  93         if (pending & SOFTIRQ_NOW_MASK)
  94                 return false;
  95         return tsk && task_is_running(tsk) && !__kthread_should_park(tsk);
  96 }
  97
  98 #ifdef CONFIG_TRACE_IRQFLAGS
  99 DEFINE_PER_CPU(int, hardirqs_enabled);
 100 DEFINE_PER_CPU(int, hardirq_context);
 101 EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
 102 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
 103 #endif
 104
 105 /*
 106  * SOFTIRQ_OFFSET usage:
 107  *
 108  * On !RT kernels 'count' is the preempt counter, on RT kernels this applies
 109  * to a per CPU counter and to task::softirqs_disabled_cnt.
 110  *
 111  * - count is changed by SOFTIRQ_OFFSET on entering or leaving softirq
 112  *   processing.
 113  *
 114  * - count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
 115  *   on local_bh_disable or local_bh_enable.
 116  *
 117  * This lets us distinguish between whether we are currently processing
 118  * softirq and whether we just have bh disabled.
 119  */
 120 #ifdef CONFIG_PREEMPT_RT
 121
 122 /*
 123  * RT accounts for BH disabled sections in task::softirqs_disabled_cnt and
 124  * also in per CPU softirq_ctrl::cnt. This is necessary to allow tasks in a
 125  * softirq disabled section to be preempted.
 126  *
 127  * The per task counter is used for softirq_count(), in_softirq() and
 128  * in_serving_softirqs() because these counts are only valid when the task
 129  * holding softirq_ctrl::lock is running.
 130  *
 131  * The per CPU counter prevents pointless wakeups of ksoftirqd in case that
 132  * the task which is in a softirq disabled section is preempted or blocks.
 133  */
 134 struct softirq_ctrl {
 135         local_lock_t    lock;
 136         int             cnt;
 137 };
 138
 139 static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl) = {
 140         .lock   = INIT_LOCAL_LOCK(softirq_ctrl.lock),
 141 };
 142
 143 /**
 144  * local_bh_blocked() - Check for idle whether BH processing is blocked
 145  *
 146  * Returns false if the per CPU softirq::cnt is 0 otherwise true.
 147  *
 148  * This is invoked from the idle task to guard against false positive
 149  * softirq pending warnings, which would happen when the task which holds
 150  * softirq_ctrl::lock was the only running task on the CPU and blocks on
 151  * some other lock.
 152  */
 153 bool local_bh_blocked(void)
 154 {
 155         return __this_cpu_read(softirq_ctrl.cnt) != 0;
 156 }
 157
 158 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 159 {
 160         unsigned long flags;
 161         int newcnt;
 162
 163         WARN_ON_ONCE(in_hardirq());
 164
 165         /* First entry of a task into a BH disabled section? */
 166         if (!current->softirq_disable_cnt) {
 167                 if (preemptible()) {
 168                         local_lock(&softirq_ctrl.lock);
 169                         /* Required to meet the RCU bottomhalf requirements. */
 170                         rcu_read_lock();
 171                 } else {
 172                         DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt));
 173                 }
 174         }
 175
 176         /*
 177          * Track the per CPU softirq disabled state. On RT this is per CPU
 178          * state to allow preemption of bottom half disabled sections.
 179          */
 180         newcnt = __this_cpu_add_return(softirq_ctrl.cnt, cnt);
 181         /*
 182          * Reflect the result in the task state to prevent recursion on the
 183          * local lock and to make softirq_count() & al work.
 184          */
 185         current->softirq_disable_cnt = newcnt;
 186
 187         if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) {
 188                 raw_local_irq_save(flags);
 189                 lockdep_softirqs_off(ip);
 190                 raw_local_irq_restore(flags);
 191         }
 192 }
 193 EXPORT_SYMBOL(__local_bh_disable_ip);
 194
 195 static void __local_bh_enable(unsigned int cnt, bool unlock)
 196 {
 197         unsigned long flags;
 198         int newcnt;
 199
 200         DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=
 201                             this_cpu_read(softirq_ctrl.cnt));
 202
 203         if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() == cnt) {
 204                 raw_local_irq_save(flags);
 205                 lockdep_softirqs_on(_RET_IP_);
 206                 raw_local_irq_restore(flags);
 207         }
 208
 209         newcnt = __this_cpu_sub_return(softirq_ctrl.cnt, cnt);
 210         current->softirq_disable_cnt = newcnt;
 211
 212         if (!newcnt && unlock) {
 213                 rcu_read_unlock();
 214                 local_unlock(&softirq_ctrl.lock);
 215         }
 216 }
 217
 218 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 219 {
 220         bool preempt_on = preemptible();
 221         unsigned long flags;
 222         u32 pending;
 223         int curcnt;
 224
 225         WARN_ON_ONCE(in_hardirq());
 226         lockdep_assert_irqs_enabled();
 227
 228         local_irq_save(flags);
 229         curcnt = __this_cpu_read(softirq_ctrl.cnt);
 230
 231         /*
 232          * If this is not reenabling soft interrupts, no point in trying to
 233          * run pending ones.
 234          */
 235         if (curcnt != cnt)
 236                 goto out;
 237
 238         pending = local_softirq_pending();
 239         if (!pending || ksoftirqd_running(pending))
 240                 goto out;
 241
 242         /*
 243          * If this was called from non preemptible context, wake up the
 244          * softirq daemon.
 245          */
 246         if (!preempt_on) {
 247                 wakeup_softirqd();
 248                 goto out;
 249         }
 250
 251         /*
 252          * Adjust softirq count to SOFTIRQ_OFFSET which makes
 253          * in_serving_softirq() become true.
 254          */
 255         cnt = SOFTIRQ_OFFSET;
 256         __local_bh_enable(cnt, false);
 257         __do_softirq();
 258
 259 out:
 260         __local_bh_enable(cnt, preempt_on);
 261         local_irq_restore(flags);
 262 }
 263 EXPORT_SYMBOL(__local_bh_enable_ip);
 264
 265 /*
 266  * Invoked from ksoftirqd_run() outside of the interrupt disabled section
 267  * to acquire the per CPU local lock for reentrancy protection.
 268  */
 269 static inline void ksoftirqd_run_begin(void)
 270 {
 271         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 272         local_irq_disable();
 273 }
 274
 275 /* Counterpart to ksoftirqd_run_begin() */
 276 static inline void ksoftirqd_run_end(void)
 277 {
 278         __local_bh_enable(SOFTIRQ_OFFSET, true);
 279         WARN_ON_ONCE(in_interrupt());
 280         local_irq_enable();
 281 }
 282
 283 static inline void softirq_handle_begin(void) { }
 284 static inline void softirq_handle_end(void) { }
 285
 286 static inline bool should_wake_ksoftirqd(void)
 287 {
 288         return !this_cpu_read(softirq_ctrl.cnt);
 289 }
 290
 291 static inline void invoke_softirq(void)
 292 {
 293         if (should_wake_ksoftirqd())
 294                 wakeup_softirqd();
 295 }
 296
 297 /*
 298  * flush_smp_call_function_queue() can raise a soft interrupt in a function
 299  * call. On RT kernels this is undesired and the only known functionality
 300  * in the block layer which does this is disabled on RT. If soft interrupts
 301  * get raised which haven't been raised before the flush, warn so it can be
 302  * investigated.
 303  */
 304 void do_softirq_post_smp_call_flush(unsigned int was_pending)
 305 {
 306         if (WARN_ON_ONCE(was_pending != local_softirq_pending()))
 307                 invoke_softirq();
 308 }
 309
 310 #else /* CONFIG_PREEMPT_RT */
 311
 312 /*
 313  * This one is for softirq.c-internal use, where hardirqs are disabled
 314  * legitimately:
 315  */
 316 #ifdef CONFIG_TRACE_IRQFLAGS
 317 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 318 {
 319         unsigned long flags;
 320
 321         WARN_ON_ONCE(in_hardirq());
 322
 323         raw_local_irq_save(flags);
 324         /*
 325          * The preempt tracer hooks into preempt_count_add and will break
 326          * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 327          * is set and before current->softirq_enabled is cleared.
 328          * We must manually increment preempt_count here and manually
 329          * call the trace_preempt_off later.
 330          */
 331         __preempt_count_add(cnt);
 332         /*
 333          * Were softirqs turned off above:
 334          */
 335         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 336                 lockdep_softirqs_off(ip);
 337         raw_local_irq_restore(flags);
 338
 339         if (preempt_count() == cnt) {
 340 #ifdef CONFIG_DEBUG_PREEMPT
 341                 current->preempt_disable_ip = get_lock_parent_ip();
 342 #endif
 343                 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
 344         }
 345 }
 346 EXPORT_SYMBOL(__local_bh_disable_ip);
 347 #endif /* CONFIG_TRACE_IRQFLAGS */
 348
 349 static void __local_bh_enable(unsigned int cnt)
 350 {
 351         lockdep_assert_irqs_disabled();
 352
 353         if (preempt_count() == cnt)
 354                 trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 355
 356         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 357                 lockdep_softirqs_on(_RET_IP_);
 358
 359         __preempt_count_sub(cnt);
 360 }
 361
 362 /*
 363  * Special-case - softirqs can safely be enabled by __do_softirq(),
 364  * without processing still-pending softirqs:
 365  */
 366 void _local_bh_enable(void)
 367 {
 368         WARN_ON_ONCE(in_hardirq());
 369         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 370 }
 371 EXPORT_SYMBOL(_local_bh_enable);
 372
 373 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 374 {
 375         WARN_ON_ONCE(in_hardirq());
 376         lockdep_assert_irqs_enabled();
 377 #ifdef CONFIG_TRACE_IRQFLAGS
 378         local_irq_disable();
 379 #endif
 380         /*
 381          * Are softirqs going to be turned on now:
 382          */
 383         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 384                 lockdep_softirqs_on(ip);
 385         /*
 386          * Keep preemption disabled until we are done with
 387          * softirq processing:
 388          */
 389         __preempt_count_sub(cnt - 1);
 390
 391         if (unlikely(!in_interrupt() && local_softirq_pending())) {
 392                 /*
 393                  * Run softirq if any pending. And do it in its own stack
 394                  * as we may be calling this deep in a task call stack already.
 395                  */
 396                 do_softirq();
 397         }
 398
 399         preempt_count_dec();
 400 #ifdef CONFIG_TRACE_IRQFLAGS
 401         local_irq_enable();
 402 #endif
 403         preempt_check_resched();
 404 }
 405 EXPORT_SYMBOL(__local_bh_enable_ip);
 406
 407 static inline void softirq_handle_begin(void)
 408 {
 409         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 410 }
 411
 412 static inline void softirq_handle_end(void)
 413 {
 414         __local_bh_enable(SOFTIRQ_OFFSET);
 415         WARN_ON_ONCE(in_interrupt());
 416 }
 417
 418 static inline void ksoftirqd_run_begin(void)
 419 {
 420         local_irq_disable();
 421 }
 422
 423 static inline void ksoftirqd_run_end(void)
 424 {
 425         local_irq_enable();
 426 }
 427
 428 static inline bool should_wake_ksoftirqd(void)
 429 {
 430         return true;
 431 }
 432
 433 static inline void invoke_softirq(void)
 434 {
 435         if (ksoftirqd_running(local_softirq_pending()))
 436                 return;
 437
 438         if (!force_irqthreads() || !__this_cpu_read(ksoftirqd)) {
 439 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 440                 /*
 441                  * We can safely execute softirq on the current stack if
 442                  * it is the irq stack, because it should be near empty
 443                  * at this stage.
 444                  */
 445                 __do_softirq();
 446 #else
 447                 /*
 448                  * Otherwise, irq_exit() is called on the task stack that can
 449                  * be potentially deep already. So call softirq in its own stack
 450                  * to prevent from any overrun.
 451                  */
 452                 do_softirq_own_stack();
 453 #endif
 454         } else {
 455                 wakeup_softirqd();
 456         }
 457 }
 458
 459 asmlinkage __visible void do_softirq(void)
 460 {
 461         __u32 pending;
 462         unsigned long flags;
 463
 464         if (in_interrupt())
 465                 return;
 466
 467         local_irq_save(flags);
 468
 469         pending = local_softirq_pending();
 470
 471         if (pending && !ksoftirqd_running(pending))
 472                 do_softirq_own_stack();
 473
 474         local_irq_restore(flags);
 475 }
 476
 477 #endif /* !CONFIG_PREEMPT_RT */
 478
 479 /*
 480  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 481  * but break the loop if need_resched() is set or after 2 ms.
 482  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 483  * certain cases, such as stop_machine(), jiffies may cease to
 484  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 485  * well to make sure we eventually return from this method.
 486  *
 487  * These limits have been established via experimentation.
 488  * The two things to balance is latency against fairness -
 489  * we want to handle softirqs as soon as possible, but they
 490  * should not be able to lock up the box.
 491  */
 492 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 493 #define MAX_SOFTIRQ_RESTART 10
 494
 495 #ifdef CONFIG_TRACE_IRQFLAGS
 496 /*
 497  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 498  * to keep the lockdep irq context tracking as tight as possible in order to
 499  * not miss-qualify lock contexts and miss possible deadlocks.
 500  */
 501
 502 static inline bool lockdep_softirq_start(void)
 503 {
 504         bool in_hardirq = false;
 505
 506         if (lockdep_hardirq_context()) {
 507                 in_hardirq = true;
 508                 lockdep_hardirq_exit();
 509         }
 510
 511         lockdep_softirq_enter();
 512
 513         return in_hardirq;
 514 }
 515
 516 static inline void lockdep_softirq_end(bool in_hardirq)
 517 {
 518         lockdep_softirq_exit();
 519
 520         if (in_hardirq)
 521                 lockdep_hardirq_enter();
 522 }
 523 #else
 524 static inline bool lockdep_softirq_start(void) { return false; }
 525 static inline void lockdep_softirq_end(bool in_hardirq) { }
 526 #endif
 527
 528 asmlinkage __visible void __softirq_entry __do_softirq(void)
 529 {
 530         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 531         unsigned long old_flags = current->flags;
 532         int max_restart = MAX_SOFTIRQ_RESTART;
 533         struct softirq_action *h;
 534         bool in_hardirq;
 535         __u32 pending;
 536         int softirq_bit;
 537
 538         /*
 539          * Mask out PF_MEMALLOC as the current task context is borrowed for the
 540          * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
 541          * again if the socket is related to swapping.
 542          */
 543         current->flags &= ~PF_MEMALLOC;
 544
 545         pending = local_softirq_pending();
 546
 547         softirq_handle_begin();
 548         in_hardirq = lockdep_softirq_start();
 549         account_softirq_enter(current);
 550
 551 restart:
 552         /* Reset the pending bitmask before enabling irqs */
 553         set_softirq_pending(0);
 554
 555         local_irq_enable();
 556
 557         h = softirq_vec;
 558
 559         while ((softirq_bit = ffs(pending))) {
 560                 unsigned int vec_nr;
 561                 int prev_count;
 562
 563                 h += softirq_bit - 1;
 564
 565                 vec_nr = h - softirq_vec;
 566                 prev_count = preempt_count();
 567
 568                 kstat_incr_softirqs_this_cpu(vec_nr);
 569
 570                 trace_softirq_entry(vec_nr);
 571                 h->action(h);
 572                 trace_softirq_exit(vec_nr);
 573                 if (unlikely(prev_count != preempt_count())) {
 574                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 575                                vec_nr, softirq_to_name[vec_nr], h->action,
 576                                prev_count, preempt_count());
 577                         preempt_count_set(prev_count);
 578                 }
 579                 h++;
 580                 pending >>= softirq_bit;
 581         }
 582
 583         if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
 584             __this_cpu_read(ksoftirqd) == current)
 585                 rcu_softirq_qs();
 586
 587         local_irq_disable();
 588
 589         pending = local_softirq_pending();
 590         if (pending) {
 591                 if (time_before(jiffies, end) && !need_resched() &&
 592                     --max_restart)
 593                         goto restart;
 594
 595                 wakeup_softirqd();
 596         }
 597
 598         account_softirq_exit(current);
 599         lockdep_softirq_end(in_hardirq);
 600         softirq_handle_end();
 601         current_restore_flags(old_flags, PF_MEMALLOC);
 602 }
 603
 604 /**
 605  * irq_enter_rcu - Enter an interrupt context with RCU watching
 606  */
 607 void irq_enter_rcu(void)
 608 {
 609         __irq_enter_raw();
 610
 611         if (tick_nohz_full_cpu(smp_processor_id()) ||
 612             (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET)))
 613                 tick_irq_enter();
 614
 615         account_hardirq_enter(current);
 616 }
 617
 618 /**
 619  * irq_enter - Enter an interrupt context including RCU update
 620  */
 621 void irq_enter(void)
 622 {
 623         rcu_irq_enter();
 624         irq_enter_rcu();
 625 }
 626
 627 static inline void tick_irq_exit(void)
 628 {
 629 #ifdef CONFIG_NO_HZ_COMMON
 630         int cpu = smp_processor_id();
 631
 632         /* Make sure that timer wheel updates are propagated */
 633         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 634                 if (!in_hardirq())
 635                         tick_nohz_irq_exit();
 636         }
 637 #endif
 638 }
 639
 640 static inline void __irq_exit_rcu(void)
 641 {
 642 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 643         local_irq_disable();
 644 #else
 645         lockdep_assert_irqs_disabled();
 646 #endif
 647         account_hardirq_exit(current);
 648         preempt_count_sub(HARDIRQ_OFFSET);
 649         if (!in_interrupt() && local_softirq_pending())
 650                 invoke_softirq();
 651
 652         tick_irq_exit();
 653 }
 654
 655 /**
 656  * irq_exit_rcu() - Exit an interrupt context without updating RCU
 657  *
 658  * Also processes softirqs if needed and possible.
 659  */
 660 void irq_exit_rcu(void)
 661 {
 662         __irq_exit_rcu();
 663          /* must be last! */
 664         lockdep_hardirq_exit();
 665 }
 666
 667 /**
 668  * irq_exit - Exit an interrupt context, update RCU and lockdep
 669  *
 670  * Also processes softirqs if needed and possible.
 671  */
 672 void irq_exit(void)
 673 {
 674         __irq_exit_rcu();
 675         rcu_irq_exit();
 676          /* must be last! */
 677         lockdep_hardirq_exit();
 678 }
 679
 680 /*
 681  * This function must run with irqs disabled!
 682  */
 683 inline void raise_softirq_irqoff(unsigned int nr)
 684 {
 685         __raise_softirq_irqoff(nr);
 686
 687         /*
 688          * If we're in an interrupt or softirq, we're done
 689          * (this also catches softirq-disabled code). We will
 690          * actually run the softirq once we return from
 691          * the irq or softirq.
 692          *
 693          * Otherwise we wake up ksoftirqd to make sure we
 694          * schedule the softirq soon.
 695          */
 696         if (!in_interrupt() && should_wake_ksoftirqd())
 697                 wakeup_softirqd();
 698 }
 699
 700 void raise_softirq(unsigned int nr)
 701 {
 702         unsigned long flags;
 703
 704         local_irq_save(flags);
 705         raise_softirq_irqoff(nr);
 706         local_irq_restore(flags);
 707 }
 708
 709 void __raise_softirq_irqoff(unsigned int nr)
 710 {
 711         lockdep_assert_irqs_disabled();
 712         trace_softirq_raise(nr);
 713         or_softirq_pending(1UL << nr);
 714 }
 715
 716 void open_softirq(int nr, void (*action)(struct softirq_action *))
 717 {
 718         softirq_vec[nr].action = action;
 719 }
 720
 721 /*
 722  * Tasklets
 723  */
 724 struct tasklet_head {
 725         struct tasklet_struct *head;
 726         struct tasklet_struct **tail;
 727 };
 728
 729 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 730 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 731
 732 static void __tasklet_schedule_common(struct tasklet_struct *t,
 733                                       struct tasklet_head __percpu *headp,
 734                                       unsigned int softirq_nr)
 735 {
 736         struct tasklet_head *head;
 737         unsigned long flags;
 738
 739         local_irq_save(flags);
 740         head = this_cpu_ptr(headp);
 741         t->next = NULL;
 742         *head->tail = t;
 743         head->tail = &(t->next);
 744         raise_softirq_irqoff(softirq_nr);
 745         local_irq_restore(flags);
 746 }
 747
 748 void __tasklet_schedule(struct tasklet_struct *t)
 749 {
 750         __tasklet_schedule_common(t, &tasklet_vec,
 751                                   TASKLET_SOFTIRQ);
 752 }
 753 EXPORT_SYMBOL(__tasklet_schedule);
 754
 755 void __tasklet_hi_schedule(struct tasklet_struct *t)
 756 {
 757         __tasklet_schedule_common(t, &tasklet_hi_vec,
 758                                   HI_SOFTIRQ);
 759 }
 760 EXPORT_SYMBOL(__tasklet_hi_schedule);
 761
 762 static bool tasklet_clear_sched(struct tasklet_struct *t)
 763 {
 764         if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
 765                 wake_up_var(&t->state);
 766                 return true;
 767         }
 768
 769         WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
 770                   t->use_callback ? "callback" : "func",
 771                   t->use_callback ? (void *)t->callback : (void *)t->func);
 772
 773         return false;
 774 }
 775
 776 static void tasklet_action_common(struct softirq_action *a,
 777                                   struct tasklet_head *tl_head,
 778                                   unsigned int softirq_nr)
 779 {
 780         struct tasklet_struct *list;
 781
 782         local_irq_disable();
 783         list = tl_head->head;
 784         tl_head->head = NULL;
 785         tl_head->tail = &tl_head->head;
 786         local_irq_enable();
 787
 788         while (list) {
 789                 struct tasklet_struct *t = list;
 790
 791                 list = list->next;
 792
 793                 if (tasklet_trylock(t)) {
 794                         if (!atomic_read(&t->count)) {
 795                                 if (tasklet_clear_sched(t)) {
 796                                         if (t->use_callback)
 797                                                 t->callback(t);
 798                                         else
 799                                                 t->func(t->data);
 800                                 }
 801                                 tasklet_unlock(t);
 802                                 continue;
 803                         }
 804                         tasklet_unlock(t);
 805                 }
 806
 807                 local_irq_disable();
 808                 t->next = NULL;
 809                 *tl_head->tail = t;
 810                 tl_head->tail = &t->next;
 811                 __raise_softirq_irqoff(softirq_nr);
 812                 local_irq_enable();
 813         }
 814 }
 815
 816 static __latent_entropy void tasklet_action(struct softirq_action *a)
 817 {
 818         tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
 819 }
 820
 821 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
 822 {
 823         tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
 824 }
 825
 826 void tasklet_setup(struct tasklet_struct *t,
 827                    void (*callback)(struct tasklet_struct *))
 828 {
 829         t->next = NULL;
 830         t->state = 0;
 831         atomic_set(&t->count, 0);
 832         t->callback = callback;
 833         t->use_callback = true;
 834         t->data = 0;
 835 }
 836 EXPORT_SYMBOL(tasklet_setup);
 837
 838 void tasklet_init(struct tasklet_struct *t,
 839                   void (*func)(unsigned long), unsigned long data)
 840 {
 841         t->next = NULL;
 842         t->state = 0;
 843         atomic_set(&t->count, 0);
 844         t->func = func;
 845         t->use_callback = false;
 846         t->data = data;
 847 }
 848 EXPORT_SYMBOL(tasklet_init);
 849
 850 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 851 /*
 852  * Do not use in new code. Waiting for tasklets from atomic contexts is
 853  * error prone and should be avoided.
 854  */
 855 void tasklet_unlock_spin_wait(struct tasklet_struct *t)
 856 {
 857         while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
 858                 if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 859                         /*
 860                          * Prevent a live lock when current preempted soft
 861                          * interrupt processing or prevents ksoftirqd from
 862                          * running. If the tasklet runs on a different CPU
 863                          * then this has no effect other than doing the BH
 864                          * disable/enable dance for nothing.
 865                          */
 866                         local_bh_disable();
 867                         local_bh_enable();
 868                 } else {
 869                         cpu_relax();
 870                 }
 871         }
 872 }
 873 EXPORT_SYMBOL(tasklet_unlock_spin_wait);
 874 #endif
 875
 876 void tasklet_kill(struct tasklet_struct *t)
 877 {
 878         if (in_interrupt())
 879                 pr_notice("Attempt to kill tasklet from interrupt\n");
 880
 881         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
 882                 wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
 883
 884         tasklet_unlock_wait(t);
 885         tasklet_clear_sched(t);
 886 }
 887 EXPORT_SYMBOL(tasklet_kill);
 888
 889 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 890 void tasklet_unlock(struct tasklet_struct *t)
 891 {
 892         smp_mb__before_atomic();
 893         clear_bit(TASKLET_STATE_RUN, &t->state);
 894         smp_mb__after_atomic();
 895         wake_up_var(&t->state);
 896 }
 897 EXPORT_SYMBOL_GPL(tasklet_unlock);
 898
 899 void tasklet_unlock_wait(struct tasklet_struct *t)
 900 {
 901         wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));
 902 }
 903 EXPORT_SYMBOL_GPL(tasklet_unlock_wait);
 904 #endif
 905
 906 void __init softirq_init(void)
 907 {
 908         int cpu;
 909
 910         for_each_possible_cpu(cpu) {
 911                 per_cpu(tasklet_vec, cpu).tail =
 912                         &per_cpu(tasklet_vec, cpu).head;
 913                 per_cpu(tasklet_hi_vec, cpu).tail =
 914                         &per_cpu(tasklet_hi_vec, cpu).head;
 915         }
 916
 917         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 918         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 919 }
 920
 921 static int ksoftirqd_should_run(unsigned int cpu)
 922 {
 923         return local_softirq_pending();
 924 }
 925
 926 static void run_ksoftirqd(unsigned int cpu)
 927 {
 928         ksoftirqd_run_begin();
 929         if (local_softirq_pending()) {
 930                 /*
 931                  * We can safely run softirq on inline stack, as we are not deep
 932                  * in the task stack here.
 933                  */
 934                 __do_softirq();
 935                 ksoftirqd_run_end();
 936                 cond_resched();
 937                 return;
 938         }
 939         ksoftirqd_run_end();
 940 }
 941
 942 #ifdef CONFIG_HOTPLUG_CPU
 943 static int takeover_tasklets(unsigned int cpu)
 944 {
 945         /* CPU is dead, so no lock needed. */
 946         local_irq_disable();
 947
 948         /* Find end, append list for that CPU. */
 949         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 950                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 951                 __this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 952                 per_cpu(tasklet_vec, cpu).head = NULL;
 953                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 954         }
 955         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 956
 957         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 958                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 959                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 960                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 961                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 962         }
 963         raise_softirq_irqoff(HI_SOFTIRQ);
 964
 965         local_irq_enable();
 966         return 0;
 967 }
 968 #else
 969 #define takeover_tasklets       NULL
 970 #endif /* CONFIG_HOTPLUG_CPU */
 971
 972 static struct smp_hotplug_thread softirq_threads = {
 973         .store                  = &ksoftirqd,
 974         .thread_should_run      = ksoftirqd_should_run,
 975         .thread_fn              = run_ksoftirqd,
 976         .thread_comm            = "ksoftirqd/%u",
 977 };
 978
 979 static __init int spawn_ksoftirqd(void)
 980 {
 981         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
 982                                   takeover_tasklets);
 983         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 984
 985         return 0;
 986 }
 987 early_initcall(spawn_ksoftirqd);
 988
 989 /*
 990  * [ These __weak aliases are kept in a separate compilation unit, so that
 991  *   GCC does not inline them incorrectly. ]
 992  */
 993
 994 int __init __weak early_irq_init(void)
 995 {
 996         return 0;
 997 }
 998
 999 int __init __weak arch_probe_nr_irqs(void)
1000 {
1001         return NR_IRQS_LEGACY;
1002 }
1003
1004 int __init __weak arch_early_irq_init(void)
1005 {
1006         return 0;
1007 }
1008
1009 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
1010 {
1011         return from;
1012 }