initial Olimex linux tree from Daniel, originally Feb 3, 2016

1 files changed, 1215 insertions, 0 deletions

diff --git a/linux/kernel/softirq.c b/linux/kernel/softirq.c
new file mode 100644
index 00000000..0fd93311
--- /dev/null
+++ b/linux/kernel/softirq.c
@@ -0,0 +1,1215 @@
+/*
+ *	linux/kernel/softirq.c
+ *
+ *	Copyright (C) 1992 Linus Torvalds
+ *
+ *	Distribute under GPLv2.
+ *
+ *	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/delay.h>
+#include <linux/ftrace.h>
+#include <linux/smp.h>
+#include <linux/smpboot.h>
+#include <linux/tick.h>
+#include <linux/locallock.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
+irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
+EXPORT_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", "BLOCK_IOPOLL",
+	"TASKLET", "SCHED", "HRTIMER", "RCU"
+};
+
+#ifdef CONFIG_NO_HZ_COMMON
+# ifdef CONFIG_PREEMPT_RT_FULL
+
+struct softirq_runner {
+	struct task_struct *runner[NR_SOFTIRQS];
+};
+
+static DEFINE_PER_CPU(struct softirq_runner, softirq_runners);
+
+static inline void softirq_set_runner(unsigned int sirq)
+{
+	struct softirq_runner *sr = this_cpu_ptr(&softirq_runners);
+
+	sr->runner[sirq] = current;
+}
+
+static inline void softirq_clr_runner(unsigned int sirq)
+{
+	struct softirq_runner *sr = this_cpu_ptr(&softirq_runners);
+
+	sr->runner[sirq] = NULL;
+}
+
+/*
+ * On preempt-rt a softirq running context might be blocked on a
+ * lock. There might be no other runnable task on this CPU because the
+ * lock owner runs on some other CPU. So we have to go into idle with
+ * the pending bit set. Therefor we need to check this otherwise we
+ * warn about false positives which confuses users and defeats the
+ * whole purpose of this test.
+ *
+ * This code is called with interrupts disabled.
+ */
+void softirq_check_pending_idle(void)
+{
+	static int rate_limit;
+	struct softirq_runner *sr = this_cpu_ptr(&softirq_runners);
+	u32 warnpending;
+	int i;
+
+	if (rate_limit >= 10)
+		return;
+
+	warnpending = local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK;
+	for (i = 0; i < NR_SOFTIRQS; i++) {
+		struct task_struct *tsk = sr->runner[i];
+
+		/*
+		 * The wakeup code in rtmutex.c wakes up the task
+		 * _before_ it sets pi_blocked_on to NULL under
+		 * tsk->pi_lock. So we need to check for both: state
+		 * and pi_blocked_on.
+		 */
+		if (tsk) {
+			raw_spin_lock(&tsk->pi_lock);
+			if (tsk->pi_blocked_on || tsk->state == TASK_RUNNING) {
+				/* Clear all bits pending in that task */
+				warnpending &= ~(tsk->softirqs_raised);
+				warnpending &= ~(1 << i);
+			}
+			raw_spin_unlock(&tsk->pi_lock);
+		}
+	}
+
+	if (warnpending) {
+		printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
+		       warnpending);
+		rate_limit++;
+	}
+}
+# else
+/*
+ * On !PREEMPT_RT we just printk rate limited:
+ */
+void softirq_check_pending_idle(void)
+{
+	static int rate_limit;
+
+	if (rate_limit < 10 &&
+			(local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
+		printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
+		       local_softirq_pending());
+		rate_limit++;
+	}
+}
+# endif
+
+#else /* !CONFIG_NO_HZ_COMMON */
+static inline void softirq_set_runner(unsigned int sirq) { }
+static inline void softirq_clr_runner(unsigned int sirq) { }
+#endif
+
+/*
+ * 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);
+}
+
+static void handle_softirq(unsigned int vec_nr)
+{
+	struct softirq_action *h = softirq_vec + vec_nr;
+	int prev_count;
+
+	prev_count = preempt_count();
+
+	kstat_incr_softirqs_this_cpu(vec_nr);
+
+	trace_softirq_entry(vec_nr);
+	h->action(h);
+	trace_softirq_exit(vec_nr);
+	if (unlikely(prev_count != preempt_count())) {
+		pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
+		       vec_nr, softirq_to_name[vec_nr], h->action,
+		       prev_count, preempt_count());
+		preempt_count_set(prev_count);
+	}
+}
+
+#ifndef CONFIG_PREEMPT_RT_FULL
+static inline int ksoftirqd_softirq_pending(void)
+{
+	return local_softirq_pending();
+}
+
+static void handle_pending_softirqs(u32 pending)
+{
+	struct softirq_action *h = softirq_vec;
+	int softirq_bit;
+
+	local_irq_enable();
+
+	h = softirq_vec;
+
+	while ((softirq_bit = ffs(pending))) {
+		unsigned int vec_nr;
+
+		h += softirq_bit - 1;
+		vec_nr = h - softirq_vec;
+		handle_softirq(vec_nr);
+
+		h++;
+		pending >>= softirq_bit;
+	}
+
+	rcu_bh_qs();
+	local_irq_disable();
+}
+
+static void run_ksoftirqd(unsigned int cpu)
+{
+	local_irq_disable();
+	if (ksoftirqd_softirq_pending()) {
+		__do_softirq();
+		local_irq_enable();
+		cond_resched_rcu_qs();
+		return;
+	}
+	local_irq_enable();
+}
+
+/*
+ * 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.
+ */
+
+/*
+ * This one is for softirq.c-internal use,
+ * where hardirqs are disabled legitimately:
+ */
+#ifdef CONFIG_TRACE_IRQFLAGS
+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))
+		trace_softirqs_off(ip);
+	raw_local_irq_restore(flags);
+
+	if (preempt_count() == cnt) {
+#ifdef CONFIG_DEBUG_PREEMPT
+		current->preempt_disable_ip = get_parent_ip(CALLER_ADDR1);
+#endif
+		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
+	}
+}
+EXPORT_SYMBOL(__local_bh_disable_ip);
+#endif /* CONFIG_TRACE_IRQFLAGS */
+
+static void __local_bh_enable(unsigned int cnt)
+{
+	WARN_ON_ONCE(!irqs_disabled());
+
+	if (softirq_count() == (cnt & SOFTIRQ_MASK))
+		trace_softirqs_on(_RET_IP_);
+	preempt_count_sub(cnt);
+}
+
+/*
+ * Special-case - softirqs can safely be enabled in
+ * cond_resched_softirq(), or 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() || irqs_disabled());
+#ifdef CONFIG_TRACE_IRQFLAGS
+	local_irq_disable();
+#endif
+	/*
+	 * Are softirqs going to be turned on now:
+	 */
+	if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
+		trace_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);
+
+/*
+ * 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 (trace_hardirq_context(current)) {
+		in_hardirq = true;
+		trace_hardirq_exit();
+	}
+
+	lockdep_softirq_enter();
+
+	return in_hardirq;
+}
+
+static inline void lockdep_softirq_end(bool in_hardirq)
+{
+	lockdep_softirq_exit();
+
+	if (in_hardirq)
+		trace_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 __do_softirq(void)
+{
+	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
+	unsigned long old_flags = current->flags;
+	int max_restart = MAX_SOFTIRQ_RESTART;
+	bool in_hardirq;
+	__u32 pending;
+
+	/*
+	 * Mask out PF_MEMALLOC s 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 swap
+	 */
+	current->flags &= ~PF_MEMALLOC;
+
+	pending = local_softirq_pending();
+	account_irq_enter_time(current);
+
+	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
+	in_hardirq = lockdep_softirq_start();
+
+restart:
+	/* Reset the pending bitmask before enabling irqs */
+	set_softirq_pending(0);
+
+	handle_pending_softirqs(pending);
+
+	pending = local_softirq_pending();
+	if (pending) {
+		if (time_before(jiffies, end) && !need_resched() &&
+		    --max_restart)
+			goto restart;
+
+		wakeup_softirqd();
+	}
+
+	lockdep_softirq_end(in_hardirq);
+	account_irq_exit_time(current);
+	__local_bh_enable(SOFTIRQ_OFFSET);
+	WARN_ON_ONCE(in_interrupt());
+	tsk_restore_flags(current, old_flags, PF_MEMALLOC);
+}
+
+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)
+		do_softirq_own_stack();
+
+	local_irq_restore(flags);
+}
+
+/*
+ * This function must run with irqs disabled!
+ */
+void raise_softirq_irqoff(unsigned int nr)
+{
+	__raise_softirq_irqoff(nr);
+
+	/*
+	 * If we're in an interrupt or softirq, we're done
+	 * (this also catches softirq-disabled code). We will
+	 * actually run the softirq once we return from
+	 * the irq or softirq.
+	 *
+	 * Otherwise we wake up ksoftirqd to make sure we
+	 * schedule the softirq soon.
+	 */
+	if (!in_interrupt())
+		wakeup_softirqd();
+}
+
+void __raise_softirq_irqoff(unsigned int nr)
+{
+	trace_softirq_raise(nr);
+	or_softirq_pending(1UL << nr);
+}
+
+static inline void local_bh_disable_nort(void) { local_bh_disable(); }
+static inline void _local_bh_enable_nort(void) { _local_bh_enable(); }
+static void ksoftirqd_set_sched_params(unsigned int cpu) { }
+static void ksoftirqd_clr_sched_params(unsigned int cpu, bool online) { }
+
+#else /* !PREEMPT_RT_FULL */
+
+/*
+ * On RT we serialize softirq execution with a cpu local lock per softirq
+ */
+static DEFINE_PER_CPU(struct local_irq_lock [NR_SOFTIRQS], local_softirq_locks);
+
+void __init softirq_early_init(void)
+{
+	int i;
+
+	for (i = 0; i < NR_SOFTIRQS; i++)
+		local_irq_lock_init(local_softirq_locks[i]);
+}
+
+static void lock_softirq(int which)
+{
+	local_lock(local_softirq_locks[which]);
+}
+
+static void unlock_softirq(int which)
+{
+	local_unlock(local_softirq_locks[which]);
+}
+
+static void do_single_softirq(int which)
+{
+	unsigned long old_flags = current->flags;
+
+	current->flags &= ~PF_MEMALLOC;
+	vtime_account_irq_enter(current);
+	current->flags |= PF_IN_SOFTIRQ;
+	lockdep_softirq_enter();
+	local_irq_enable();
+	handle_softirq(which);
+	local_irq_disable();
+	lockdep_softirq_exit();
+	current->flags &= ~PF_IN_SOFTIRQ;
+	vtime_account_irq_enter(current);
+	tsk_restore_flags(current, old_flags, PF_MEMALLOC);
+}
+
+/*
+ * Called with interrupts disabled. Process softirqs which were raised
+ * in current context (or on behalf of ksoftirqd).
+ */
+static void do_current_softirqs(void)
+{
+	while (current->softirqs_raised) {
+		int i = __ffs(current->softirqs_raised);
+		unsigned int pending, mask = (1U << i);
+
+		current->softirqs_raised &= ~mask;
+		local_irq_enable();
+
+		/*
+		 * If the lock is contended, we boost the owner to
+		 * process the softirq or leave the critical section
+		 * now.
+		 */
+		lock_softirq(i);
+		local_irq_disable();
+		softirq_set_runner(i);
+		/*
+		 * Check with the local_softirq_pending() bits,
+		 * whether we need to process this still or if someone
+		 * else took care of it.
+		 */
+		pending = local_softirq_pending();
+		if (pending & mask) {
+			set_softirq_pending(pending & ~mask);
+			do_single_softirq(i);
+		}
+		softirq_clr_runner(i);
+		unlock_softirq(i);
+		WARN_ON(current->softirq_nestcnt != 1);
+	}
+}
+
+void __local_bh_disable(void)
+{
+	if (++current->softirq_nestcnt == 1)
+		migrate_disable();
+}
+EXPORT_SYMBOL(__local_bh_disable);
+
+void __local_bh_enable(void)
+{
+	if (WARN_ON(current->softirq_nestcnt == 0))
+		return;
+
+	local_irq_disable();
+	if (current->softirq_nestcnt == 1 && current->softirqs_raised)
+		do_current_softirqs();
+	local_irq_enable();
+
+	if (--current->softirq_nestcnt == 0)
+		migrate_enable();
+}
+EXPORT_SYMBOL(__local_bh_enable);
+
+void _local_bh_enable(void)
+{
+	if (WARN_ON(current->softirq_nestcnt == 0))
+		return;
+	if (--current->softirq_nestcnt == 0)
+		migrate_enable();
+}
+EXPORT_SYMBOL(_local_bh_enable);
+
+int in_serving_softirq(void)
+{
+	return current->flags & PF_IN_SOFTIRQ;
+}
+EXPORT_SYMBOL(in_serving_softirq);
+
+/* Called with preemption disabled */
+static void run_ksoftirqd(unsigned int cpu)
+{
+	local_irq_disable();
+	current->softirq_nestcnt++;
+
+	do_current_softirqs();
+	current->softirq_nestcnt--;
+	rcu_note_context_switch();
+	local_irq_enable();
+}
+
+/*
+ * Called from netif_rx_ni(). Preemption enabled, but migration
+ * disabled. So the cpu can't go away under us.
+ */
+void thread_do_softirq(void)
+{
+	if (!in_serving_softirq() && current->softirqs_raised) {
+		current->softirq_nestcnt++;
+		do_current_softirqs();
+		current->softirq_nestcnt--;
+	}
+}
+
+static void do_raise_softirq_irqoff(unsigned int nr)
+{
+	trace_softirq_raise(nr);
+	or_softirq_pending(1UL << nr);
+
+	/*
+	 * If we are not in a hard interrupt and inside a bh disabled
+	 * region, we simply raise the flag on current. local_bh_enable()
+	 * will make sure that the softirq is executed. Otherwise we
+	 * delegate it to ksoftirqd.
+	 */
+	if (!in_irq() && current->softirq_nestcnt)
+		current->softirqs_raised |= (1U << nr);
+	else if (__this_cpu_read(ksoftirqd))
+		__this_cpu_read(ksoftirqd)->softirqs_raised |= (1U << nr);
+}
+
+void __raise_softirq_irqoff(unsigned int nr)
+{
+	do_raise_softirq_irqoff(nr);
+	if (!in_irq() && !current->softirq_nestcnt)
+		wakeup_softirqd();
+}
+
+/*
+ * This function must run with irqs disabled!
+ */
+void raise_softirq_irqoff(unsigned int nr)
+{
+	do_raise_softirq_irqoff(nr);
+
+	/*
+	 * If we're in an hard interrupt we let irq return code deal
+	 * with the wakeup of ksoftirqd.
+	 */
+	if (in_irq())
+		return;
+	/*
+	 * If we are in thread context but outside of a bh disabled
+	 * region, we need to wake ksoftirqd as well.
+	 *
+	 * CHECKME: Some of the places which do that could be wrapped
+	 * into local_bh_disable/enable pairs. Though it's unclear
+	 * whether this is worth the effort. To find those places just
+	 * raise a WARN() if the condition is met.
+	 */
+	if (!current->softirq_nestcnt)
+		wakeup_softirqd();
+}
+
+static inline int ksoftirqd_softirq_pending(void)
+{
+	return current->softirqs_raised;
+}
+
+static inline void local_bh_disable_nort(void) { }
+static inline void _local_bh_enable_nort(void) { }
+
+static inline void ksoftirqd_set_sched_params(unsigned int cpu)
+{
+	struct sched_param param = { .sched_priority = 1 };
+
+	sched_setscheduler(current, SCHED_FIFO, &param);
+	/* Take over all pending softirqs when starting */
+	local_irq_disable();
+	current->softirqs_raised = local_softirq_pending();
+	local_irq_enable();
+}
+
+static inline void ksoftirqd_clr_sched_params(unsigned int cpu, bool online)
+{
+	struct sched_param param = { .sched_priority = 0 };
+
+	sched_setscheduler(current, SCHED_NORMAL, &param);
+}
+
+#endif /* PREEMPT_RT_FULL */
+/*
+ * Enter an interrupt context.
+ */
+void irq_enter(void)
+{
+	rcu_irq_enter();
+	if (is_idle_task(current) && !in_interrupt()) {
+		/*
+		 * Prevent raise_softirq from needlessly waking up ksoftirqd
+		 * here, as softirq will be serviced on return from interrupt.
+		 */
+		local_bh_disable_nort();
+		tick_irq_enter();
+		_local_bh_enable_nort();
+	}
+
+	__irq_enter();
+}
+
+static inline void invoke_softirq(void)
+{
+#ifndef CONFIG_PREEMPT_RT_FULL
+	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();
+	}
+#else /* PREEMPT_RT_FULL */
+	unsigned long flags;
+
+	local_irq_save(flags);
+	if (__this_cpu_read(ksoftirqd) &&
+			__this_cpu_read(ksoftirqd)->softirqs_raised)
+		wakeup_softirqd();
+	local_irq_restore(flags);
+#endif
+}
+
+static inline void tick_irq_exit(void)
+{
+#ifdef CONFIG_NO_HZ_COMMON
+	int cpu = smp_processor_id();
+
+	/* Make sure that timer wheel updates are propagated */
+	if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
+		if (!in_interrupt())
+			tick_nohz_irq_exit();
+	}
+#endif
+}
+
+/*
+ * Exit an interrupt context. Process softirqs if needed and possible:
+ */
+void irq_exit(void)
+{
+#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
+	local_irq_disable();
+#else
+	WARN_ON_ONCE(!irqs_disabled());
+#endif
+
+	account_irq_exit_time(current);
+	preempt_count_sub(HARDIRQ_OFFSET);
+	if (!in_interrupt() && local_softirq_pending())
+		invoke_softirq();
+
+	tick_irq_exit();
+	rcu_irq_exit();
+	trace_hardirq_exit(); /* must be last! */
+}
+
+void raise_softirq(unsigned int nr)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	raise_softirq_irqoff(nr);
+	local_irq_restore(flags);
+}
+
+void open_softirq(int nr, void (*action)(struct softirq_action *))
+{
+	softirq_vec[nr].action = action;
+}
+
+/*
+ * Tasklets
+ */
+struct tasklet_head {
+	struct tasklet_struct *head;
+	struct tasklet_struct **tail;
+};
+
+static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
+static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
+
+static void inline
+__tasklet_common_schedule(struct tasklet_struct *t, struct tasklet_head *head, unsigned int nr)
+{
+	if (tasklet_trylock(t)) {
+again:
+		/* We may have been preempted before tasklet_trylock
+		 * and __tasklet_action may have already run.
+		 * So double check the sched bit while the takslet
+		 * is locked before adding it to the list.
+		 */
+		if (test_bit(TASKLET_STATE_SCHED, &t->state)) {
+			t->next = NULL;
+			*head->tail = t;
+			head->tail = &(t->next);
+			raise_softirq_irqoff(nr);
+			tasklet_unlock(t);
+		} else {
+			/* This is subtle. If we hit the corner case above
+			 * It is possible that we get preempted right here,
+			 * and another task has successfully called
+			 * tasklet_schedule(), then this function, and
+			 * failed on the trylock. Thus we must be sure
+			 * before releasing the tasklet lock, that the
+			 * SCHED_BIT is clear. Otherwise the tasklet
+			 * may get its SCHED_BIT set, but not added to the
+			 * list
+			 */
+			if (!tasklet_tryunlock(t))
+				goto again;
+		}
+	}
+}
+
+void __tasklet_schedule(struct tasklet_struct *t)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	__tasklet_common_schedule(t, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(__tasklet_schedule);
+
+void __tasklet_hi_schedule(struct tasklet_struct *t)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	__tasklet_common_schedule(t, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(__tasklet_hi_schedule);
+
+void __tasklet_hi_schedule_first(struct tasklet_struct *t)
+{
+	BUG_ON(!irqs_disabled());
+
+	__tasklet_hi_schedule(t);
+}
+EXPORT_SYMBOL(__tasklet_hi_schedule_first);
+
+void  tasklet_enable(struct tasklet_struct *t)
+{
+	if (!atomic_dec_and_test(&t->count))
+		return;
+	if (test_and_clear_bit(TASKLET_STATE_PENDING, &t->state))
+		tasklet_schedule(t);
+}
+EXPORT_SYMBOL(tasklet_enable);
+
+static void __tasklet_action(struct softirq_action *a,
+			     struct tasklet_struct *list)
+{
+	int loops = 1000000;
+
+	while (list) {
+		struct tasklet_struct *t = list;
+
+		list = list->next;
+
+		/*
+		 * Should always succeed - after a tasklist got on the
+		 * list (after getting the SCHED bit set from 0 to 1),
+		 * nothing but the tasklet softirq it got queued to can
+		 * lock it:
+		 */
+		if (!tasklet_trylock(t)) {
+			WARN_ON(1);
+			continue;
+		}
+
+		t->next = NULL;
+
+		/*
+		 * If we cannot handle the tasklet because it's disabled,
+		 * mark it as pending. tasklet_enable() will later
+		 * re-schedule the tasklet.
+		 */
+		if (unlikely(atomic_read(&t->count))) {
+out_disabled:
+			/* implicit unlock: */
+			wmb();
+			t->state = TASKLET_STATEF_PENDING;
+			continue;
+		}
+
+		/*
+		 * After this point on the tasklet might be rescheduled
+		 * on another CPU, but it can only be added to another
+		 * CPU's tasklet list if we unlock the tasklet (which we
+		 * dont do yet).
+		 */
+		if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
+			WARN_ON(1);
+
+again:
+		t->func(t->data);
+
+		/*
+		 * Try to unlock the tasklet. We must use cmpxchg, because
+		 * another CPU might have scheduled or disabled the tasklet.
+		 * We only allow the STATE_RUN -> 0 transition here.
+		 */
+		while (!tasklet_tryunlock(t)) {
+			/*
+			 * If it got disabled meanwhile, bail out:
+			 */
+			if (atomic_read(&t->count))
+				goto out_disabled;
+			/*
+			 * If it got scheduled meanwhile, re-execute
+			 * the tasklet function:
+			 */
+			if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
+				goto again;
+			if (!--loops) {
+				printk("hm, tasklet state: %08lx\n", t->state);
+				WARN_ON(1);
+				tasklet_unlock(t);
+				break;
+			}
+		}
+	}
+}
+
+static void tasklet_action(struct softirq_action *a)
+{
+	struct tasklet_struct *list;
+
+	local_irq_disable();
+
+	list = __this_cpu_read(tasklet_vec.head);
+	__this_cpu_write(tasklet_vec.head, NULL);
+	__this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
+
+	local_irq_enable();
+
+	__tasklet_action(a, list);
+}
+
+static void tasklet_hi_action(struct softirq_action *a)
+{
+	struct tasklet_struct *list;
+
+	local_irq_disable();
+
+	list = __this_cpu_read(tasklet_hi_vec.head);
+	__this_cpu_write(tasklet_hi_vec.head, NULL);
+	__this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
+
+	local_irq_enable();
+
+	__tasklet_action(a, list);
+}
+
+void tasklet_init(struct tasklet_struct *t,
+		  void (*func)(unsigned long), unsigned long data)
+{
+	t->next = NULL;
+	t->state = 0;
+	atomic_set(&t->count, 0);
+	t->func = func;
+	t->data = data;
+}
+EXPORT_SYMBOL(tasklet_init);
+
+void tasklet_kill(struct tasklet_struct *t)
+{
+	if (in_interrupt())
+		pr_notice("Attempt to kill tasklet from interrupt\n");
+
+	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
+		do {
+			msleep(1);
+		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
+	}
+	tasklet_unlock_wait(t);
+	clear_bit(TASKLET_STATE_SCHED, &t->state);
+}
+EXPORT_SYMBOL(tasklet_kill);
+
+/*
+ * tasklet_hrtimer
+ */
+
+/*
+ * The trampoline is called when the hrtimer expires. It schedules a tasklet
+ * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
+ * hrtimer callback, but from softirq context.
+ */
+static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
+{
+	struct tasklet_hrtimer *ttimer =
+		container_of(timer, struct tasklet_hrtimer, timer);
+
+	tasklet_hi_schedule(&ttimer->tasklet);
+	return HRTIMER_NORESTART;
+}
+
+/*
+ * Helper function which calls the hrtimer callback from
+ * tasklet/softirq context
+ */
+static void __tasklet_hrtimer_trampoline(unsigned long data)
+{
+	struct tasklet_hrtimer *ttimer = (void *)data;
+	enum hrtimer_restart restart;
+
+	restart = ttimer->function(&ttimer->timer);
+	if (restart != HRTIMER_NORESTART)
+		hrtimer_restart(&ttimer->timer);
+}
+
+/**
+ * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
+ * @ttimer:	 tasklet_hrtimer which is initialized
+ * @function:	 hrtimer callback function which gets called from softirq context
+ * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
+ * @mode:	 hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
+ */
+void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
+			  enum hrtimer_restart (*function)(struct hrtimer *),
+			  clockid_t which_clock, enum hrtimer_mode mode)
+{
+	hrtimer_init(&ttimer->timer, which_clock, mode);
+	ttimer->timer.function = __hrtimer_tasklet_trampoline;
+	tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
+		     (unsigned long)ttimer);
+	ttimer->function = function;
+}
+EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
+
+void __init softirq_init(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		per_cpu(tasklet_vec, cpu).tail =
+			&per_cpu(tasklet_vec, cpu).head;
+		per_cpu(tasklet_hi_vec, cpu).tail =
+			&per_cpu(tasklet_hi_vec, cpu).head;
+	}
+
+	open_softirq(TASKLET_SOFTIRQ, tasklet_action);
+	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
+}
+
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
+void tasklet_unlock_wait(struct tasklet_struct *t)
+{
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+		/*
+		 * Hack for now to avoid this busy-loop:
+		 */
+#ifdef CONFIG_PREEMPT_RT_FULL
+		msleep(1);
+#else
+		barrier();
+#endif
+	}
+}
+EXPORT_SYMBOL(tasklet_unlock_wait);
+#endif
+
+static int ksoftirqd_should_run(unsigned int cpu)
+{
+	return ksoftirqd_softirq_pending();
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * tasklet_kill_immediate is called to remove a tasklet which can already be
+ * scheduled for execution on @cpu.
+ *
+ * Unlike tasklet_kill, this function removes the tasklet
+ * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
+ *
+ * When this function is called, @cpu must be in the CPU_DEAD state.
+ */
+void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
+{
+	struct tasklet_struct **i;
+
+	BUG_ON(cpu_online(cpu));
+	BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
+
+	if (!test_bit(TASKLET_STATE_SCHED, &t->state))
+		return;
+
+	/* CPU is dead, so no lock needed. */
+	for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
+		if (*i == t) {
+			*i = t->next;
+			/* If this was the tail element, move the tail ptr */
+			if (*i == NULL)
+				per_cpu(tasklet_vec, cpu).tail = i;
+			return;
+		}
+	}
+	BUG();
+}
+
+static void takeover_tasklets(unsigned int cpu)
+{
+	/* CPU is dead, so no lock needed. */
+	local_irq_disable();
+
+	/* Find end, append list for that CPU. */
+	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
+		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
+		this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
+		per_cpu(tasklet_vec, cpu).head = NULL;
+		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
+	}
+	raise_softirq_irqoff(TASKLET_SOFTIRQ);
+
+	if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
+		*__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
+		__this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
+		per_cpu(tasklet_hi_vec, cpu).head = NULL;
+		per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
+	}
+	raise_softirq_irqoff(HI_SOFTIRQ);
+
+	local_irq_enable();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
+static int cpu_callback(struct notifier_block *nfb, unsigned long action,
+			void *hcpu)
+{
+	switch (action) {
+#ifdef CONFIG_HOTPLUG_CPU
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		takeover_tasklets((unsigned long)hcpu);
+		break;
+#endif /* CONFIG_HOTPLUG_CPU */
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cpu_nfb = {
+	.notifier_call = cpu_callback
+};
+
+static struct smp_hotplug_thread softirq_threads = {
+	.store			= &ksoftirqd,
+	.setup			= ksoftirqd_set_sched_params,
+	.cleanup		= ksoftirqd_clr_sched_params,
+	.thread_should_run	= ksoftirqd_should_run,
+	.thread_fn		= run_ksoftirqd,
+	.thread_comm		= "ksoftirqd/%u",
+};
+
+static __init int spawn_ksoftirqd(void)
+{
+	register_cpu_notifier(&cpu_nfb);
+
+	BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
+
+	return 0;
+}
+early_initcall(spawn_ksoftirqd);
+
+/*
+ * [ These __weak aliases are kept in a separate compilation unit, so that
+ *   GCC does not inline them incorrectly. ]
+ */
+
+int __init __weak early_irq_init(void)
+{
+	return 0;
+}
+
+int __init __weak arch_probe_nr_irqs(void)
+{
+	return NR_IRQS_LEGACY;
+}
+
+int __init __weak arch_early_irq_init(void)
+{
+	return 0;
+}
+
+unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
+{
+	return from;
+}