softirq: introduce tasklet_hrtimer infrastructure

commit ca109491f (hrtimer: removing all ur callback modes) moved all
hrtimer callbacks into hard interrupt context when high resolution
timers are active. That breaks code which relied on the assumption
that the callback happens in softirq context.

Provide a generic infrastructure which combines tasklets and hrtimers
together to provide an in-softirq hrtimer experience.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: torvalds@linux-foundation.org
Cc: kaber@trash.net
Cc: David Miller <davem@davemloft.net>
LKML-Reference: <1248265724.27058.1366.camel@twins>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 63 insertions, 1 deletions

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 3a94905fa5d2..eb5e131a0485 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -345,7 +345,9 @@ void open_softirq(int nr, void (*action)(struct softirq_action *))
 	softirq_vec[nr].action = action;
 }
 
-/* Tasklets */
+/*
+ * Tasklets
+ */
 struct tasklet_head
 {
 	struct tasklet_struct *head;
@@ -493,6 +495,66 @@ void tasklet_kill(struct tasklet_struct *t)
 
 EXPORT_SYMBOL(tasklet_kill);
 
+/*
+ * tasklet_hrtimer
+ */
+
+/*
+ * The trampoline is called when the hrtimer expires. If this is
+ * called from the hrtimer interrupt then we schedule the tasklet as
+ * the timer callback function expects to run in softirq context. If
+ * it's called in softirq context anyway (i.e. high resolution timers
+ * disabled) then the hrtimer callback is called right away.
+ */
+static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
+{
+	struct tasklet_hrtimer *ttimer =
+		container_of(timer, struct tasklet_hrtimer, timer);
+
+	if (hrtimer_is_hres_active(timer)) {
+		tasklet_hi_schedule(&ttimer->tasklet);
+		return HRTIMER_NORESTART;
+	}
+	return ttimer->function(timer);
+}
+
+/*
+ * 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 funtion 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);
+
+/*
+ * Remote softirq bits
+ */
+
 DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
 EXPORT_PER_CPU_SYMBOL(softirq_work_list);