sched: Add wrapper for checking task_struct::on_rq

Implement task_on_rq_queued() and use it everywhere instead of
on_rq check. No functional changes.

The only exception is we do not use the wrapper in
check_for_tasks(), because it requires to export
task_on_rq_queued() in global header files. Next patch in series
would return it back, so we do not twist it from here to there.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528052.23412.87.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/sched.h

@@ -15,6 +15,9 @@
 
 struct rq;
 
+/* task_struct::on_rq states: */
+#define TASK_ON_RQ_QUEUED	1
+
 extern __read_mostly int scheduler_running;
 
 extern unsigned long calc_load_update;
@@ -942,6 +945,10 @@ static inline int task_running(struct rq *rq, struct task_struct *p)
 #endif
 }
 
+static inline int task_on_rq_queued(struct task_struct *p)
+{
+	return p->on_rq == TASK_ON_RQ_QUEUED;
+}
 
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(next)	do { } while (0)