[PATCH] lockdep: add local_irq_enable_in_hardirq() API

Introduce local_irq_enable_in_hardirq() API.  It is currently aliased to
local_irq_enable(), hence has no functional effects.

This API will be used by lockdep, but even without lockdep this will better
document places in the kernel where a hardirq context enables hardirqs.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/interrupt.h

@@ -80,6 +80,23 @@ extern int request_irq(unsigned int,
 		       unsigned long, const char *, void *);
 extern void free_irq(unsigned int, void *);
 
+/*
+ * On lockdep we dont want to enable hardirqs in hardirq
+ * context. Use local_irq_enable_in_hardirq() to annotate
+ * kernel code that has to do this nevertheless (pretty much
+ * the only valid case is for old/broken hardware that is
+ * insanely slow).
+ *
+ * NOTE: in theory this might break fragile code that relies
+ * on hardirq delivery - in practice we dont seem to have such
+ * places left. So the only effect should be slightly increased
+ * irqs-off latencies.
+ */
+#ifdef CONFIG_LOCKDEP
+# define local_irq_enable_in_hardirq()	do { } while (0)
+#else
+# define local_irq_enable_in_hardirq()	local_irq_enable()
+#endif
 
 #ifdef CONFIG_GENERIC_HARDIRQS
 extern void disable_irq_nosync(unsigned int irq);