irq_work: Add generic hardirq context callbacks

Provide a mechanism that allows running code in IRQ context. It is
most useful for NMI code that needs to interact with the rest of the
system -- like wakeup a task to drain buffers.

Perf currently has such a mechanism, so extract that and provide it as
a generic feature, independent of perf so that others may also
benefit.

The IRQ context callback is generated through self-IPIs where
possible, or on architectures like powerpc the decrementer (the
built-in timer facility) is set to generate an interrupt immediately.

Architectures that don't have anything like this get to do with a
callback from the timer tick. These architectures can call
irq_work_run() at the tail of any IRQ handlers that might enqueue such
work (like the perf IRQ handler) to avoid undue latencies in
processing the work.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Kyle McMartin <kyle@mcmartin.ca>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[ various fixes ]
Signed-off-by: Huang Ying <ying.huang@intel.com>
LKML-Reference: <1287036094.7768.291.camel@yhuang-dev>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 164 insertions, 0 deletions

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
new file mode 100644
index 000000000000..f16763ff8481
--- /dev/null
+++ b/kernel/irq_work.c
@@ -0,0 +1,164 @@
+/*
+ * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ *
+ * Provides a framework for enqueueing and running callbacks from hardirq
+ * context. The enqueueing is NMI-safe.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/irq_work.h>
+#include <linux/hardirq.h>
+
+/*
+ * An entry can be in one of four states:
+ *
+ * free      NULL, 0 -> {claimed}       : free to be used
+ * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
+ * pending   next, 3 -> {busy}          : queued, pending callback
+ * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
+ *
+ * We use the lower two bits of the next pointer to keep PENDING and BUSY
+ * flags.
+ */
+
+#define IRQ_WORK_PENDING        1UL
+#define IRQ_WORK_BUSY           2UL
+#define IRQ_WORK_FLAGS          3UL
+
+static inline bool irq_work_is_set(struct irq_work *entry, int flags)
+{
+        return (unsigned long)entry->next & flags;
+}
+
+static inline struct irq_work *irq_work_next(struct irq_work *entry)
+{
+        unsigned long next = (unsigned long)entry->next;
+        next &= ~IRQ_WORK_FLAGS;
+        return (struct irq_work *)next;
+}
+
+static inline struct irq_work *next_flags(struct irq_work *entry, int flags)
+{
+        unsigned long next = (unsigned long)entry;
+        next |= flags;
+        return (struct irq_work *)next;
+}
+
+static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
+
+/*
+ * Claim the entry so that no one else will poke at it.
+ */
+static bool irq_work_claim(struct irq_work *entry)
+{
+        struct irq_work *next, *nflags;
+
+        do {
+                next = entry->next;
+                if ((unsigned long)next & IRQ_WORK_PENDING)
+                        return false;
+                nflags = next_flags(next, IRQ_WORK_FLAGS);
+        } while (cmpxchg(&entry->next, next, nflags) != next);
+
+        return true;
+}
+
+
+void __weak arch_irq_work_raise(void)
+{
+        /*
+         * Lame architectures will get the timer tick callback
+         */
+}
+
+/*
+ * Queue the entry and raise the IPI if needed.
+ */
+static void __irq_work_queue(struct irq_work *entry)
+{
+        struct irq_work **head, *next;
+
+        head = &get_cpu_var(irq_work_list);
+
+        do {
+                next = *head;
+                /* Can assign non-atomic because we keep the flags set. */
+                entry->next = next_flags(next, IRQ_WORK_FLAGS);
+        } while (cmpxchg(head, next, entry) != next);
+
+        /* The list was empty, raise self-interrupt to start processing. */
+        if (!irq_work_next(entry))
+                arch_irq_work_raise();
+
+        put_cpu_var(irq_work_list);
+}
+
+/*
+ * Enqueue the irq_work @entry, returns true on success, failure when the
+ * @entry was already enqueued by someone else.
+ *
+ * Can be re-enqueued while the callback is still in progress.
+ */
+bool irq_work_queue(struct irq_work *entry)
+{
+        if (!irq_work_claim(entry)) {
+                /*
+                 * Already enqueued, can't do!
+                 */
+                return false;
+        }
+
+        __irq_work_queue(entry);
+        return true;
+}
+EXPORT_SYMBOL_GPL(irq_work_queue);
+
+/*
+ * Run the irq_work entries on this cpu. Requires to be ran from hardirq
+ * context with local IRQs disabled.
+ */
+void irq_work_run(void)
+{
+        struct irq_work *list, **head;
+
+        head = &__get_cpu_var(irq_work_list);
+        if (*head == NULL)
+                return;
+
+        BUG_ON(!in_irq());
+        BUG_ON(!irqs_disabled());
+
+        list = xchg(head, NULL);
+        while (list != NULL) {
+                struct irq_work *entry = list;
+
+                list = irq_work_next(list);
+
+                /*
+                 * Clear the PENDING bit, after this point the @entry
+                 * can be re-used.
+                 */
+                entry->next = next_flags(NULL, IRQ_WORK_BUSY);
+                entry->func(entry);
+                /*
+                 * Clear the BUSY bit and return to the free state if
+                 * no-one else claimed it meanwhile.
+                 */
+                cmpxchg(&entry->next, next_flags(NULL, IRQ_WORK_BUSY), NULL);
+        }
+}
+EXPORT_SYMBOL_GPL(irq_work_run);
+
+/*
+ * Synchronize against the irq_work @entry, ensures the entry is not
+ * currently in use.
+ */
+void irq_work_sync(struct irq_work *entry)
+{
+        WARN_ON_ONCE(irqs_disabled());
+
+        while (irq_work_is_set(entry, IRQ_WORK_BUSY))
+                cpu_relax();
+}
+EXPORT_SYMBOL_GPL(irq_work_sync);