개념 설명 전체 · v6.6 / 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 ((sched_core_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 }