sched: Kill task_preempt_count()

task_preempt_count() is pointless if preemption counter is per-cpu,
currently this is x86 only. It is only valid if the task is not
running, and even in this case the only info it can provide is the
state of PREEMPT_ACTIVE bit.

Change its single caller to check p->on_rq instead, this should be
the same if p->state != TASK_RUNNING, and kill this helper.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Alexander Graf <agraf@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-arch@vger.kernel.org
Link: http://lkml.kernel.org/r/20141008183348.GC17495@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/preempt.h

@@ -30,9 +30,6 @@ static __always_inline void preempt_count_set(int pc)
 /*
  * must be macros to avoid header recursion hell
  */
-#define task_preempt_count(p) \
-	(task_thread_info(p)->saved_preempt_count & ~PREEMPT_NEED_RESCHED)
-
 #define init_task_preempt_count(p) do { \
 	task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \
 } while (0)

include/asm-generic/preempt.h

@@ -23,9 +23,6 @@ static __always_inline void preempt_count_set(int pc)
 /*
  * must be macros to avoid header recursion hell
  */
-#define task_preempt_count(p) \
-	(task_thread_info(p)->preempt_count & ~PREEMPT_NEED_RESCHED)
-
 #define init_task_preempt_count(p) do { \
 	task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \
 } while (0)

kernel/sched/core.c

@@ -1054,7 +1054,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 	 * ttwu() will sort out the placement.
 	 */
 	WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
-			!(task_preempt_count(p) & PREEMPT_ACTIVE));
+			!p->on_rq);
 
 #ifdef CONFIG_LOCKDEP
 	/*