path: root/kernel/softirq.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *	linux/kernel/softirq.c
 *
 *	Copyright (C) 1992 Linus Torvalds
 *
 *	Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/export.h>
#include <linux/kernel_stat.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/notifier.h>
#include <linux/percpu.h>
#include <linux/cpu.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/rcupdate.h>
#include <linux/ftrace.h>
#include <linux/smp.h>
#include <linux/smpboot.h>
#include <linux/tick.h>
#include <linux/irq.h>

#define CREATE_TRACE_POINTS
#include <trace/events/irq.h>

/*
   - No shared variables, all the data are CPU local.
   - If a softirq needs serialization, let it serialize itself
     by its own spinlocks.
   - Even if softirq is serialized, only local cpu is marked for
     execution. Hence, we get something sort of weak cpu binding.
     Though it is still not clear, will it result in better locality
     or will not.

   Examples:
   - NET RX softirq. It is multithreaded and does not require
     any global serialization.
   - NET TX softirq. It kicks software netdevice queues, hence
     it is logically serialized per device, but this serialization
     is invisible to common code.
   - Tasklets: serialized wrt itself.
 */

#ifndef __ARCH_IRQ_STAT
DEFINE_PER_CPU_ALIGNED(irq_cpustat_t, irq_stat);
EXPORT_PER_CPU_SYMBOL(irq_stat);
#endif

static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;

DEFINE_PER_CPU(struct task_struct *, ksoftirqd);

const char * const softirq_to_name[NR_SOFTIRQS] = {
	"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
	"TASKLET", "SCHED", "HRTIMER", "RCU"
};

/*
 * we cannot loop indefinitely here to avoid userspace starvation,
 * but we also don't want to introduce a worst case 1/HZ latency
 * to the pending events, so lets the scheduler to balance
 * the softirq load for us.
 */
static void wakeup_softirqd(void)
{
	/* Interrupts are disabled: no need to stop preemption */
	struct task_struct *tsk = __this_cpu_read(ksoftirqd);

	if (tsk && tsk->state != TASK_RUNNING)
		wake_up_process(tsk);
}

/*
 * If ksoftirqd is scheduled, we do not want to process pending softirqs
 * right now. Let ksoftirqd handle this at its own rate, to get fairness,
 * unless we're doing some of the synchronous softirqs.
 */
#define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ))
static bool ksoftirqd_running(unsigned long pending)
{
	struct task_struct *tsk = __this_cpu_read(ksoftirqd);

	if (pending & SOFTIRQ_NOW_MASK)
		return false;
	return tsk && (tsk->state == TASK_RUNNING) &&
		!__kthread_should_park(tsk);
}

#ifdef CONFIG_TRACE_IRQFLAGS
DEFINE_PER_CPU(int, hardirqs_enabled);
DEFINE_PER_CPU(int, hardirq_context);
EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
#endif

/*
 * preempt_count and SOFTIRQ_OFFSET usage:
 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
 *   softirq processing.
 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
 *   on local_bh_disable or local_bh_enable.
 * This lets us distinguish between whether we are currently processing
 * softirq and whether we just have bh disabled.
 */

#ifdef CONFIG_TRACE_IRQFLAGS
/*
 * This is for softirq.c-internal use, where hardirqs are disabled
 * legitimately:
 */
void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
{
	unsigned long flags;

	WARN_ON_ONCE(in_irq());

	raw_local_irq_save(flags);
	/*
	 * The preempt tracer hooks into preempt_count_add and will break
	 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
	 * is set and before current->softirq_enabled is cleared.
	 * We must manually increment preempt_count here and manually
	 * call the trace_preempt_off later.
	 */
	__preempt_count_add(cnt);
	/*
	 * Were softirqs turned off above:
	 */
	if (softirq_count() == (cnt & SOFTIRQ_MASK))
		lockdep_softirqs_off(ip);
	raw_local_irq_restore(flags);

	if (preempt_count() == cnt) {
#ifdef CONFIG_DEBUG_PREEMPT
		current->preempt_disable_ip = get_lock_parent_ip();
#endif
		trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
	}
}
EXPORT_SYMBOL(__local_bh_disable_ip);
#endif /* CONFIG_TRACE_IRQFLAGS */

static void __local_bh_enable(unsigned int cnt)
{
	lockdep_assert_irqs_disabled();

	if (preempt_count() == cnt)
		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());

	if (softirq_count() == (cnt & SOFTIRQ_MASK))
		lockdep_softirqs_on(_RET_IP_);

	__preempt_count_sub(cnt);
}

/*
 * Special-case - softirqs can safely be enabled by __do_softirq(),
 * without processing still-pending softirqs:
 */
void _local_bh_enable(void)
{
	WARN_ON_ONCE(in_irq());
	__local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
}
EXPORT_SYMBOL(_local_bh_enable);

void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
{
	WARN_ON_ONCE(in_irq());
	lockdep_assert_irqs_enabled();
#ifdef CONFIG_TRACE_IRQFLAGS
	local_irq_disable();
#endif
	/*
	 * Are softirqs going to be turned on now:
	 */
	if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
		lockdep_softirqs_on(ip);
	/*
	 * Keep preemption disabled until we are done with
	 * softirq processing:
	 */
	__preempt_count_sub(cnt - 1);

	if (unlikely(!in_interrupt() && local_softirq_pending())) {
		/*
		 * Run softirq if any pending. And do it in its own stack
		 * as we may be calling this deep in a task call stack already.
		 */
		do_softirq();
	}

	preempt_count_dec();
#ifdef CONFIG_TRACE_IRQFLAGS
	local_irq_enable();
#endif
	preempt_check_resched();
}
EXPORT_SYMBOL(__local_bh_enable_ip);

static inline void invoke_softirq(void)
{
	if (ksoftirqd_running(local_softirq_pending()))
		return;

	if (!force_irqthreads) {
#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
		/*
		 * We can safely execute softirq on the current stack if
		 * it is the irq stack, because it should be near empty
		 * at this stage.
		 */
		__do_softirq();
#else
		/*
		 * Otherwise, irq_exit() is called on the task stack that can
		 * be potentially deep already. So call softirq in its own stack
		 * to prevent from any overrun.
		 */
		do_softirq_own_stack();
#endif
	} else {
		wakeup_softirqd();
	}
}

asmlinkage __visible void do_softirq(void)
{
	__u32 pending;
	unsigned long flags;

	if (in_interrupt())
		return;

	local_irq_save(flags);

	pending = local_softirq_pending();

	if (pending && !ksoftirqd_running(pending))
		do_softirq_own_stack();

	local_irq_restore(flags);
}

/*
 * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
 * but break the loop if need_resched() is set or after 2 ms.
 * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
 * certain cases, such as stop_machine(), jiffies may cease to
 * increment and so we need the MAX_SOFTIRQ_RESTART limit as
 * well to make sure we eventually return from this method.
 *
 * These limits have been established via experimentation.
 * The two things to balance is latency against fairness -
 * we want to handle softirqs as soon as possible, but they
 * should not be able to lock up the box.
 */
#define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
#define MAX_SOFTIRQ_RESTART 10

#ifdef CONFIG_TRACE_IRQFLAGS
/*
 * When we run softirqs from irq_exit() and thus on the hardirq stack we need
 * to keep the lockdep irq context tracking as tight as possible in order to
 * not miss-qualify lock contexts and miss possible deadlocks.
 */

static inline bool lockdep_softirq_start(void)
{
	bool in_hardirq = false;

	if (lockdep_hardirq_context()) {
		in_hardirq = true;
		lockdep_hardirq_exit();
	}

	lockdep_softirq_enter();

	return in_hardirq;
}

static inline void lockdep_softirq_end(bool in_hardirq)
{
	lockdep_softirq_exit();

	if (in_hardirq)
		lockdep_hardirq_enter();
}
#else
static inline bool lockdep_softirq_start(void) { return false; }
static inline void lockdep_softirq_end(bool in_hardirq) { }
#endif

asmlinkage __visible void __softirq_entry __do_softirq(void)
{
	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
	unsigned long old_flags = current->flags;
	int max_restart = MAX_SOFTIRQ_RESTART;
	struct softirq_action *h;
	bool in_hardirq;
	__u32 pending;
	int softirq_bit;

	/*
	 * Mask out PF_MEMALLOC as the current task context is borrowed for the
	 * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
	 * again if the socket is related to swapping.
	 */
	current->flags &= ~PF_MEMALLOC;

	pending =