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_irq());
 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 #else /* CONFIG_PREEMPT_RT */
 298
 299 /*
 300  * This one is for softirq.c-internal use, where hardirqs are disabled
 301  * legitimately:
 302  */
 303 #ifdef CONFIG_TRACE_IRQFLAGS
 304 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 305 {
 306         unsigned long flags;
 307
 308         WARN_ON_ONCE(in_irq());
 309
 310         raw_local_irq_save(flags);
 311         /*
 312          * The preempt tracer hooks into preempt_count_add and will break
 313          * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
 314          * is set and before current->softirq_enabled is cleared.
 315          * We must manually increment preempt_count here and manually
 316          * call the trace_preempt_off later.
 317          */
 318         __preempt_count_add(cnt);
 319         /*
 320          * Were softirqs turned off above:
 321          */
 322         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 323                 lockdep_softirqs_off(ip);
 324         raw_local_irq_restore(flags);
 325
 326         if (preempt_count() == cnt) {
 327 #ifdef CONFIG_DEBUG_PREEMPT
 328                 current->preempt_disable_ip = get_lock_parent_ip();
 329 #endif
 330                 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
 331         }
 332 }
 333 EXPORT_SYMBOL(__local_bh_disable_ip);
 334 #endif /* CONFIG_TRACE_IRQFLAGS */
 335
 336 static void __local_bh_enable(unsigned int cnt)
 337 {
 338         lockdep_assert_irqs_disabled();
 339
 340         if (preempt_count() == cnt)
 341                 trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 342
 343         if (softirq_count() == (cnt & SOFTIRQ_MASK))
 344                 lockdep_softirqs_on(_RET_IP_);
 345
 346         __preempt_count_sub(cnt);
 347 }
 348
 349 /*
 350  * Special-case - softirqs can safely be enabled by __do_softirq(),
 351  * without processing still-pending softirqs:
 352  */
 353 void _local_bh_enable(void)
 354 {
 355         WARN_ON_ONCE(in_irq());
 356         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
 357 }
 358 EXPORT_SYMBOL(_local_bh_enable);
 359
 360 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 361 {
 362         WARN_ON_ONCE(in_irq());
 363         lockdep_assert_irqs_enabled();
 364 #ifdef CONFIG_TRACE_IRQFLAGS
 365         local_irq_disable();
 366 #endif
 367         /*
 368          * Are softirqs going to be turned on now:
 369          */
 370         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
 371                 lockdep_softirqs_on(ip);
 372         /*
 373          * Keep preemption disabled until we are done with
 374          * softirq processing:
 375          */
 376         __preempt_count_sub(cnt - 1);
 377
 378         if (unlikely(!in_interrupt() && local_softirq_pending())) {
 379                 /*
 380                  * Run softirq if any pending. And do it in its own stack
 381                  * as we may be calling this deep in a task call stack already.
 382                  */
 383                 do_softirq();
 384         }
 385
 386         preempt_count_dec();
 387 #ifdef CONFIG_TRACE_IRQFLAGS
 388         local_irq_enable();
 389 #endif
 390         preempt_check_resched();
 391 }
 392 EXPORT_SYMBOL(__local_bh_enable_ip);
 393
 394 static inline void softirq_handle_begin(void)
 395 {
 396         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 397 }
 398
 399 static inline void softirq_handle_end(void)
 400 {
 401         __local_bh_enable(SOFTIRQ_OFFSET);
 402         WARN_ON_ONCE(in_interrupt());
 403 }
 404
 405 static inline void ksoftirqd_run_begin(void)
 406 {
 407         local_irq_disable();
 408 }
 409
 410 static inline void ksoftirqd_run_end(void)
 411 {
 412         local_irq_enable();
 413 }
 414
 415 static inline bool should_wake_ksoftirqd(void)
 416 {
 417         return true;
 418 }
 419
 420 static inline void invoke_softirq(void)
 421 {
 422         if (ksoftirqd_running(local_softirq_pending()))
 423                 return;
 424
 425         if (!force_irqthreads || !__this_cpu_read(ksoftirqd)) {
 426 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
 427                 /*
 428                  * We can safely execute softirq on the current stack if
 429                  * it is the irq stack, because it should be near empty
 430                  * at this stage.
 431                  */
 432                 __do_softirq();
 433 #else
 434                 /*
 435                  * Otherwise, irq_exit() is called on the task stack that can
 436                  * be potentially deep already. So call softirq in its own stack
 437                  * to prevent from any overrun.
 438                  */
 439                 do_softirq_own_stack();
 440 #endif
 441         } else {
 442                 wakeup_softirqd();
 443         }
 444 }
 445
 446 asmlinkage __visible void do_softirq(void)
 447 {
 448         __u32 pending;
 449         unsigned long flags;
 450
 451         if (in_interrupt())
 452                 return;
 453
 454         local_irq_save(flags);
 455
 456         pending = local_softirq_pending();
 457
 458         if (pending && !ksoftirqd_running(pending))
 459                 do_softirq_own_stack();
 460
 461         local_irq_restore(flags);
 462 }
 463
 464 #endif /* !CONFIG_PREEMPT_RT */
 465
 466 /*
 467  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 468  * but break the loop if need_resched() is set or after 2 ms.
 469  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 470  * certain cases, such as stop_machine(), jiffies may cease to
 471  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 472  * well to make sure we eventually return from this method.
 473  *
 474  * These limits have been established via experimentation.
 475  * The two things to balance is latency against fairness -
 476  * we want to handle softirqs as soon as possible, but they
 477  * should not be able to lock up the box.
 478  */
 479 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
 480 #define MAX_SOFTIRQ_RESTART 10
 481
 482 #ifdef CONFIG_TRACE_IRQFLAGS
 483 /*
 484  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 485  * to keep the lockdep irq context tracking as tight as possible in order to
 486  * not miss-qualify lock contexts and miss possible deadlocks.
 487  */
 488
 489 static inline bool lockdep_softirq_start(void)
 490 {
 491         bool in_hardirq = false;
 492
 493         if (lockdep_hardirq_context()) {
 494                 in_hardirq = true;
 495                 lockdep_hardirq_exit();
 496         }
 497
 498         lockdep_softirq_enter();
 499
 500         return in_hardirq;
 501 }
 502
 503 static inline void lockdep_softirq_end(bool in_hardirq)
 504 {
 505         lockdep_softirq_exit();
 506
 507         if (in_hardirq)
 508                 lockdep_hardirq_enter();
 509 }
 510 #else
 511 static inline bool lockdep_softirq_start(void) { return false; }
 512 static inline void lockdep_softirq_end(bool in_hardirq) { }
 513 #endif
 514
 515 asmlinkage __visible void __softirq_entry __do_softirq(void)
 516 {
 517         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 518         unsigned long old_flags = current->flags;
 519         int max_restart = MAX_SOFTIRQ_RESTART;
 520         struct softirq_action *h;
 521         bool in_hardirq;
 522         __u32 pending;
 523         int softirq_bit;
 524
 525         /*
 526          * Mask out PF_MEMALLOC as the current task context is borrowed for the
 527          * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
 528          * again if the socket is related to swapping.
 529          */
 530         current->flags &= ~PF_MEMALLOC;
 531
 532         pending = local_softirq_pending();
 533
 534         softirq_handle_begin();
 535         in_hardirq = lockdep_softirq_start();
 536         account_softirq_enter(current);
 537
 538 restart:
 539         /* Reset the pending bitmask before enabling irqs */
 540         set_softirq_pending(0);
 541
 542         local_irq_enable();
 543
 544         h = softirq_vec;
 545
 546         while ((softirq_bit = ffs(pending))) {
 547                 unsigned int vec_nr;
 548                 int prev_count;
 549
 550                 h += softirq_bit - 1;
 551
 552                 vec_nr = h - softirq_vec;
 553                 prev_count = preempt_count();
 554
 555                 kstat_incr_softirqs_this_cpu(vec_nr);
 556
 557                 trace_softirq_entry(vec_nr);
 558                 h->action(h);
 559                 trace_softirq_exit(vec_nr);
 560                 if (unlikely(prev_count != preempt_count())) {
 561                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
 562                                vec_nr, softirq_to_name[vec_nr], h->action,
 563                                prev_count, preempt_count());
 564                         preempt_count_set(prev_count);
 565                 }
 566                 h++;
 567                 pending >>= softirq_bit;
 568         }
 569
 570         if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
 571             __this_cpu_read(ksoftirqd) == current)
 572                 rcu_softirq_qs();
 573
 574         local_irq_disable();
 575
 576         pending = local_softirq_pending();
 577         if (pending) {
 578                 if (time_before(jiffies, end) && !need_resched() &&
 579                     --max_restart)
 580                         goto restart;
 581
 582                 wakeup_softirqd();
 583         }
 584
 585         account_softirq_exit(current);
 586         lockdep_softirq_end(in_hardirq);
 587         softirq_handle_end();
 588         current_restore_flags(old_flags, PF_MEMALLOC);
 589 }
 590
 591 /**
 592  * irq_enter_rcu - Enter an interrupt context with RCU watching
 593  */
 594 void irq_enter_rcu(void)
 595 {
 596         __irq_enter_raw();
 597
 598         if (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET))
 599                 tick_irq_enter();
 600
 601         account_hardirq_enter(current);
 602 }
 603
 604 /**
 605  * irq_enter - Enter an interrupt context including RCU update
 606  */
 607 void irq_enter(void)
 608 {
 609         rcu_irq_enter();
 610         irq_enter_rcu();
 611 }
 612
 613 static inline void tick_irq_exit(void)
 614 {
 615 #ifdef CONFIG_NO_HZ_COMMON
 616         int cpu = smp_processor_id();
 617
 618         /* Make sure that timer wheel updates are propagated */
 619         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
 620                 if (!in_irq())
 621                         tick_nohz_irq_exit();
 622         }
 623 #endif
 624 }
 625
 626 static inline void __irq_exit_rcu(void)
 627 {
 628 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 629         local_irq_disable();
 630 #else
 631         lockdep_assert_irqs_disabled();
 632 #endif
 633         account_hardirq_exit(current);
 634         preempt_count_sub(HARDIRQ_OFFSET);
 635         if (!in_interrupt() && local_softirq_pending())
 636                 invoke_softirq();
 637
 638         tick_irq_exit();
 639 }
 640
 641 /**
 642  * irq_exit_rcu() - Exit an interrupt context without updating RCU
 643  *
 644  * Also processes softirqs if needed and possible.
 645  */
 646 void irq_exit_rcu(void)
 647 {
 648         __irq_exit_rcu();
 649          /* must be last! */
 650         lockdep_hardirq_exit();
 651 }
 652
 653 /**
 654  * irq_exit - Exit an interrupt context, update RCU and lockdep
 655  *
 656  * Also processes softirqs if needed and possible.
 657  */
 658 void irq_exit(void)
 659 {
 660         __irq_exit_rcu();
 661         rcu_irq_exit();
 662          /* must be last! */
 663         lockdep_hardirq_exit();
 664 }
 665
 666 /*
 667  * This function must run with irqs disabled!
 668  */
 669 inline void raise_softirq_irqoff(unsigned int nr)
 670 {
 671         __raise_softirq_irqoff(nr);
 672
 673         /*
 674          * If we're in an interrupt or softirq, we're done
 675          * (this also catches softirq-disabled code). We will
 676          * actually run the softirq once we return from
 677          * the irq or softirq.
 678          *
 679          * Otherwise we wake up ksoftirqd to make sure we
 680          * schedule the softirq soon.
 681          */
 682         if (!in_interrupt() && should_wake_ksoftirqd())
 683                 wakeup_softirqd();
 684 }
 685
 686 void raise_softirq(unsigned int nr)
 687 {
 688         unsigned long flags;
 689
 690         local_irq_save(flags);
 691         raise_softirq_irqoff(nr);
 692         local_irq_restore(flags);
 693 }
 694
 695 void __raise_softirq_irqoff(unsigned int nr)
 696 {
 697         lockdep_assert_irqs_disabled();
 698         trace_softirq_raise(nr);
 699         or_softirq_pending(1UL << nr);
 700 }
 701
 702 void open_softirq(int nr, void (*action)(struct softirq_action *))
 703 {
 704         softirq_vec[nr].action = action;
 705 }
 706
 707 /*
 708  * Tasklets
 709  */
 710 struct tasklet_head {
 711         struct tasklet_struct *head;
 712         struct tasklet_struct **tail;
 713 };
 714
 715 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
 716 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
 717
 718 static void __tasklet_schedule_common(struct tasklet_struct *t,
 719                                       struct tasklet_head __percpu *headp,
 720                                       unsigned int softirq_nr)
 721 {
 722         struct tasklet_head *head;
 723         unsigned long flags;
 724
 725         local_irq_save(flags);
 726         head = this_cpu_ptr(headp);
 727         t->next = NULL;
 728         *head->tail = t;
 729         head->tail = &(t->next);
 730         raise_softirq_irqoff(softirq_nr);
 731         local_irq_restore(flags);
 732 }
 733
 734 void __tasklet_schedule(struct tasklet_struct *t)
 735 {
 736         __tasklet_schedule_common(t, &tasklet_vec,
 737                                   TASKLET_SOFTIRQ);
 738 }
 739 EXPORT_SYMBOL(__tasklet_schedule);
 740
 741 void __tasklet_hi_schedule(struct tasklet_struct *t)
 742 {
 743         __tasklet_schedule_common(t, &tasklet_hi_vec,
 744                                   HI_SOFTIRQ);
 745 }
 746 EXPORT_SYMBOL(__tasklet_hi_schedule);
 747
 748 static bool tasklet_clear_sched(struct tasklet_struct *t)
 749 {
 750         if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
 751                 wake_up_var(&t->state);
 752                 return true;
 753         }
 754
 755         WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
 756                   t->use_callback ? "callback" : "func",
 757                   t->use_callback ? (void *)t->callback : (void *)t->func);
 758
 759         return false;
 760 }
 761
 762 static void tasklet_action_common(struct softirq_action *a,
 763                                   struct tasklet_head *tl_head,
 764                                   unsigned int softirq_nr)
 765 {
 766         struct tasklet_struct *list;
 767
 768         local_irq_disable();
 769         list = tl_head->head;
 770         tl_head->head = NULL;
 771         tl_head->tail = &tl_head->head;
 772         local_irq_enable();
 773
 774         while (list) {
 775                 struct tasklet_struct *t = list;
 776
 777                 list = list->next;
 778
 779                 if (tasklet_trylock(t)) {
 780                         if (!atomic_read(&t->count)) {
 781                                 if (tasklet_clear_sched(t)) {
 782                                         if (t->use_callback)
 783                                                 t->callback(t);
 784                                         else
 785                                                 t->func(t->data);
 786                                 }
 787                                 tasklet_unlock(t);
 788                                 continue;
 789                         }
 790                         tasklet_unlock(t);
 791                 }
 792
 793                 local_irq_disable();
 794                 t->next = NULL;
 795                 *tl_head->tail = t;
 796                 tl_head->tail = &t->next;
 797                 __raise_softirq_irqoff(softirq_nr);
 798                 local_irq_enable();
 799         }
 800 }
 801
 802 static __latent_entropy void tasklet_action(struct softirq_action *a)
 803 {
 804         tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
 805 }
 806
 807 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
 808 {
 809         tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
 810 }
 811
 812 void tasklet_setup(struct tasklet_struct *t,
 813                    void (*callback)(struct tasklet_struct *))
 814 {
 815         t->next = NULL;
 816         t->state = 0;
 817         atomic_set(&t->count, 0);
 818         t->callback = callback;
 819         t->use_callback = true;
 820         t->data = 0;
 821 }
 822 EXPORT_SYMBOL(tasklet_setup);
 823
 824 void tasklet_init(struct tasklet_struct *t,
 825                   void (*func)(unsigned long), unsigned long data)
 826 {
 827         t->next = NULL;
 828         t->state = 0;
 829         atomic_set(&t->count, 0);
 830         t->func = func;
 831         t->use_callback = false;
 832         t->data = data;
 833 }
 834 EXPORT_SYMBOL(tasklet_init);
 835
 836 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 837 /*
 838  * Do not use in new code. Waiting for tasklets from atomic contexts is
 839  * error prone and should be avoided.
 840  */
 841 void tasklet_unlock_spin_wait(struct tasklet_struct *t)
 842 {
 843         while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
 844                 if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 845                         /*
 846                          * Prevent a live lock when current preempted soft
 847                          * interrupt processing or prevents ksoftirqd from
 848                          * running. If the tasklet runs on a different CPU
 849                          * then this has no effect other than doing the BH
 850                          * disable/enable dance for nothing.
 851                          */
 852                         local_bh_disable();
 853                         local_bh_enable();
 854                 } else {
 855                         cpu_relax();
 856                 }
 857         }
 858 }
 859 EXPORT_SYMBOL(tasklet_unlock_spin_wait);
 860 #endif
 861
 862 void tasklet_kill(struct tasklet_struct *t)
 863 {
 864         if (in_interrupt())
 865                 pr_notice("Attempt to kill tasklet from interrupt\n");
 866
 867         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
 868                 wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
 869
 870         tasklet_unlock_wait(t);
 871         tasklet_clear_sched(t);
 872 }
 873 EXPORT_SYMBOL(tasklet_kill);
 874
 875 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 876 void tasklet_unlock(struct tasklet_struct *t)
 877 {
 878         smp_mb__before_atomic();
 879         clear_bit(TASKLET_STATE_RUN, &t->state);
 880         smp_mb__after_atomic();
 881         wake_up_var(&t->state);
 882 }
 883 EXPORT_SYMBOL_GPL(tasklet_unlock);
 884
 885 void tasklet_unlock_wait(struct tasklet_struct *t)
 886 {
 887         wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));
 888 }
 889 EXPORT_SYMBOL_GPL(tasklet_unlock_wait);
 890 #endif
 891
 892 void __init softirq_init(void)
 893 {
 894         int cpu;
 895
 896         for_each_possible_cpu(cpu) {
 897                 per_cpu(tasklet_vec, cpu).tail =
 898                         &per_cpu(tasklet_vec, cpu).head;
 899                 per_cpu(tasklet_hi_vec, cpu).tail =
 900                         &per_cpu(tasklet_hi_vec, cpu).head;
 901         }
 902
 903         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 904         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 905 }
 906
 907 static int ksoftirqd_should_run(unsigned int cpu)
 908 {
 909         return local_softirq_pending();
 910 }
 911
 912 static void run_ksoftirqd(unsigned int cpu)
 913 {
 914         ksoftirqd_run_begin();
 915         if (local_softirq_pending()) {
 916                 /*
 917                  * We can safely run softirq on inline stack, as we are not deep
 918                  * in the task stack here.
 919                  */
 920                 __do_softirq();
 921                 ksoftirqd_run_end();
 922                 cond_resched();
 923                 return;
 924         }
 925         ksoftirqd_run_end();
 926 }
 927
 928 #ifdef CONFIG_HOTPLUG_CPU
 929 static int takeover_tasklets(unsigned int cpu)
 930 {
 931         /* CPU is dead, so no lock needed. */
 932         local_irq_disable();
 933
 934         /* Find end, append list for that CPU. */
 935         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 936                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
 937                 __this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 938                 per_cpu(tasklet_vec, cpu).head = NULL;
 939                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 940         }
 941         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 942
 943         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
 944                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
 945                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
 946                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
 947                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
 948         }
 949         raise_softirq_irqoff(HI_SOFTIRQ);
 950
 951         local_irq_enable();
 952         return 0;
 953 }
 954 #else
 955 #define takeover_tasklets       NULL
 956 #endif /* CONFIG_HOTPLUG_CPU */
 957
 958 static struct smp_hotplug_thread softirq_threads = {
 959         .store                  = &ksoftirqd,
 960         .thread_should_run      = ksoftirqd_should_run,
 961         .thread_fn              = run_ksoftirqd,
 962         .thread_comm            = "ksoftirqd/%u",
 963 };
 964
 965 static __init int spawn_ksoftirqd(void)
 966 {
 967         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
 968                                   takeover_tasklets);
 969         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
 970
 971         return 0;
 972 }
 973 early_initcall(spawn_ksoftirqd);
 974
 975 /*
 976  * [ These __weak aliases are kept in a separate compilation unit, so that
 977  *   GCC does not inline them incorrectly. ]
 978  */
 979
 980 int __init __weak early_irq_init(void)
 981 {
 982         return 0;
 983 }
 984
 985 int __init __weak arch_probe_nr_irqs(void)
 986 {
 987         return NR_IRQS_LEGACY;
 988 }
 989
 990 int __init __weak arch_early_irq_init(void)
 991 {
 992         return 0;
 993 }
 994
 995 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
 996 {
 997         return from;
 998 }