v4.19.13 snapshot.
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
new file mode 100644
index 0000000..6b7cdf1
--- /dev/null
+++ b/kernel/irq_work.c
@@ -0,0 +1,195 @@
+/*
+ * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
+ *
+ * Provides a framework for enqueueing and running callbacks from hardirq
+ * context. The enqueueing is NMI-safe.
+ */
+
+#include <linux/bug.h>
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/irq_work.h>
+#include <linux/percpu.h>
+#include <linux/hardirq.h>
+#include <linux/irqflags.h>
+#include <linux/sched.h>
+#include <linux/tick.h>
+#include <linux/cpu.h>
+#include <linux/notifier.h>
+#include <linux/smp.h>
+#include <asm/processor.h>
+
+
+static DEFINE_PER_CPU(struct llist_head, raised_list);
+static DEFINE_PER_CPU(struct llist_head, lazy_list);
+
+/*
+ * Claim the entry so that no one else will poke at it.
+ */
+static bool irq_work_claim(struct irq_work *work)
+{
+ unsigned long flags, oflags, nflags;
+
+ /*
+ * Start with our best wish as a premise but only trust any
+ * flag value after cmpxchg() result.
+ */
+ flags = work->flags & ~IRQ_WORK_PENDING;
+ for (;;) {
+ nflags = flags | IRQ_WORK_CLAIMED;
+ oflags = cmpxchg(&work->flags, flags, nflags);
+ if (oflags == flags)
+ break;
+ if (oflags & IRQ_WORK_PENDING)
+ return false;
+ flags = oflags;
+ cpu_relax();
+ }
+
+ return true;
+}
+
+void __weak arch_irq_work_raise(void)
+{
+ /*
+ * Lame architectures will get the timer tick callback
+ */
+}
+
+/*
+ * Enqueue the irq_work @work on @cpu unless it's already pending
+ * somewhere.
+ *
+ * Can be re-enqueued while the callback is still in progress.
+ */
+bool irq_work_queue_on(struct irq_work *work, int cpu)
+{
+ /* All work should have been flushed before going offline */
+ WARN_ON_ONCE(cpu_is_offline(cpu));
+
+#ifdef CONFIG_SMP
+
+ /* Arch remote IPI send/receive backend aren't NMI safe */
+ WARN_ON_ONCE(in_nmi());
+
+ /* Only queue if not already pending */
+ if (!irq_work_claim(work))
+ return false;
+
+ if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
+ arch_send_call_function_single_ipi(cpu);
+
+#else /* #ifdef CONFIG_SMP */
+ irq_work_queue(work);
+#endif /* #else #ifdef CONFIG_SMP */
+
+ return true;
+}
+
+/* Enqueue the irq work @work on the current CPU */
+bool irq_work_queue(struct irq_work *work)
+{
+ /* Only queue if not already pending */
+ if (!irq_work_claim(work))
+ return false;
+
+ /* Queue the entry and raise the IPI if needed. */
+ preempt_disable();
+
+ /* If the work is "lazy", handle it from next tick if any */
+ if (work->flags & IRQ_WORK_LAZY) {
+ if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
+ tick_nohz_tick_stopped())
+ arch_irq_work_raise();
+ } else {
+ if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
+ arch_irq_work_raise();
+ }
+
+ preempt_enable();
+
+ return true;
+}
+EXPORT_SYMBOL_GPL(irq_work_queue);
+
+bool irq_work_needs_cpu(void)
+{
+ struct llist_head *raised, *lazy;
+
+ raised = this_cpu_ptr(&raised_list);
+ lazy = this_cpu_ptr(&lazy_list);
+
+ if (llist_empty(raised) || arch_irq_work_has_interrupt())
+ if (llist_empty(lazy))
+ return false;
+
+ /* All work should have been flushed before going offline */
+ WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
+
+ return true;
+}
+
+static void irq_work_run_list(struct llist_head *list)
+{
+ struct irq_work *work, *tmp;
+ struct llist_node *llnode;
+ unsigned long flags;
+
+ BUG_ON(!irqs_disabled());
+
+ if (llist_empty(list))
+ return;
+
+ llnode = llist_del_all(list);
+ llist_for_each_entry_safe(work, tmp, llnode, llnode) {
+ /*
+ * Clear the PENDING bit, after this point the @work
+ * can be re-used.
+ * Make it immediately visible so that other CPUs trying
+ * to claim that work don't rely on us to handle their data
+ * while we are in the middle of the func.
+ */
+ flags = work->flags & ~IRQ_WORK_PENDING;
+ xchg(&work->flags, flags);
+
+ work->func(work);
+ /*
+ * Clear the BUSY bit and return to the free state if
+ * no-one else claimed it meanwhile.
+ */
+ (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
+ }
+}
+
+/*
+ * hotplug calls this through:
+ * hotplug_cfd() -> flush_smp_call_function_queue()
+ */
+void irq_work_run(void)
+{
+ irq_work_run_list(this_cpu_ptr(&raised_list));
+ irq_work_run_list(this_cpu_ptr(&lazy_list));
+}
+EXPORT_SYMBOL_GPL(irq_work_run);
+
+void irq_work_tick(void)
+{
+ struct llist_head *raised = this_cpu_ptr(&raised_list);
+
+ if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
+ irq_work_run_list(raised);
+ irq_work_run_list(this_cpu_ptr(&lazy_list));
+}
+
+/*
+ * Synchronize against the irq_work @entry, ensures the entry is not
+ * currently in use.
+ */
+void irq_work_sync(struct irq_work *work)
+{
+ lockdep_assert_irqs_enabled();
+
+ while (work->flags & IRQ_WORK_BUSY)
+ cpu_relax();
+}
+EXPORT_SYMBOL_GPL(irq_work_sync);