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>
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2721f07..fd4c9c6 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -14,6 +14,7 @@
 #include <linux/irqflags.h>
 #include <linux/smp.h>
 #include <linux/percpu.h>
+#include <linux/hrtimer.h>
 
 #include <asm/atomic.h>
 #include <asm/ptrace.h>
@@ -517,6 +518,31 @@
 extern void tasklet_init(struct tasklet_struct *t,
 			 void (*func)(unsigned long), unsigned long data);
 
+struct tasklet_hrtimer {
+	struct hrtimer		timer;
+	struct tasklet_struct	tasklet;
+	enum hrtimer_restart	(*function)(struct hrtimer *);
+};
+
+extern void
+tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
+		     enum hrtimer_restart (*function)(struct hrtimer *),
+		     clockid_t which_clock, enum hrtimer_mode mode);
+
+static inline
+int tasklet_hrtimer_start(struct tasklet_hrtimer *ttimer, ktime_t time,
+			  const enum hrtimer_mode mode)
+{
+	return hrtimer_start(&ttimer->timer, time, mode);
+}
+
+static inline
+void tasklet_hrtimer_cancel(struct tasklet_hrtimer *ttimer)
+{
+	hrtimer_cancel(&ttimer->timer);
+	tasklet_kill(&ttimer->tasklet);
+}
+
 /*
  * Autoprobing for irqs:
  *