Markers Implementation for RCU Preempt Tracing

This patch converts Preempt RCU Tracing code infrastructure to implement markers.

- The rcupreempt_trace structure has been moved to the tracing infrastructure and de-linked from the rcupreempt.c code. A per-cpu instance of rcupreempt_trace structure will be maintained in rcupreempt_trace.c

- The above change also renders a few macro definitions unused (such as RCU_TRACE_CPU, RCU_TRACE_ME and RCU_TRACE_RDP) which have been removed.

- Some of the helper functions in rcupreempt.c which were exported only when CONFIG_RCU_TRACE was set are now exported unconditionally. These functions operate on per-cpu variables that are used both by the RCU and RCU Tracing code. The changes help in making RCU Tracing code operate as a kernel module also.

- The references to rcupreempt-boost tracing in the module initialisation and cleanup have been removed here to enable kernel build, but will be brought in after enclosing them inside a #ifdef CONFIG_PREEMPT_RCU_BOOST.

---
 include/linux/rcupreempt.h       |   10 ----
 include/linux/rcupreempt_trace.h |   56 +++++++++++++-----------
 kernel/Kconfig.preempt           |    7 +--
 kernel/rcupreempt.c              |   90 +++++++++++++--------------------------
 kernel/rcupreempt_trace.c        |   79 ++++++++++++++++++++++++++++++++--
 5 files changed, 140 insertions(+), 102 deletions(-)

Index: linux-2.6.24-rc2-rt1.MARKER_PATCHES_NEW/include/linux/rcupreempt.h
===================================================================
@@ -96,16 +96,6 @@ extern int  rcu_pending_rt(int cpu);
 struct softirq_action;
 extern void rcu_process_callbacks_rt(struct softirq_action *unused);
 
-#ifdef CONFIG_RCU_TRACE
-struct rcupreempt_trace;
-extern int *rcupreempt_flipctr(int cpu);
-extern long rcupreempt_data_completed(void);
-extern int rcupreempt_flip_flag(int cpu);
-extern int rcupreempt_mb_flag(int cpu);
-extern char *rcupreempt_try_flip_state_name(void);
-extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu);
-#endif
-
 struct softirq_action;
 
 #ifdef CONFIG_NO_HZ

Index: linux-2.6.24-rc2-rt1.MARKER_PATCHES_NEW/kernel/Kconfig.preempt
===================================================================
@@ -172,14 +172,15 @@ config PREEMPT_RCU_BOOST
 	  possible OOM problems.
 
 config RCU_TRACE
-	bool "Enable tracing for RCU - currently stats in debugfs"
+	tristate "Enable tracing for RCU - currently stats in debugfs"
 	select DEBUG_FS
-	default y
+	select MARKERS
+	default m
 	help
 	  This option provides tracing in RCU which presents stats
 	  in debugfs for debugging RCU implementation.
 
-	  Say Y here if you want to enable RCU tracing
+	  Say Y/M here if you want to enable RCU tracing in-kernel/module.
 	  Say N if you are unsure.
 
 config SPINLOCK_BKL