sched/headers, cgroups: Remove the threadgroup_change_*() wrappery

threadgroup_change_begin()/end() is a pointless wrapper around
cgroup_threadgroup_change_begin()/end(), minus a might_sleep()
in the !CONFIG_CGROUPS=y case.

Remove the wrappery, move the might_sleep() (the down_read()
already has a might_sleep() check).

This debloats <linux/sched.h> a bit and simplifies this API.

Update all call sites.

No change in functionality.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/fs/exec.c b/fs/exec.c
index 698a860..e595e15 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1088,7 +1088,7 @@
 		struct task_struct *leader = tsk->group_leader;
 
 		for (;;) {
-			threadgroup_change_begin(tsk);
+			cgroup_threadgroup_change_begin(tsk);
 			write_lock_irq(&tasklist_lock);
 			/*
 			 * Do this under tasklist_lock to ensure that
@@ -1099,7 +1099,7 @@
 				break;
 			__set_current_state(TASK_KILLABLE);
 			write_unlock_irq(&tasklist_lock);
-			threadgroup_change_end(tsk);
+			cgroup_threadgroup_change_end(tsk);
 			schedule();
 			if (unlikely(__fatal_signal_pending(tsk)))
 				goto killed;
@@ -1157,7 +1157,7 @@
 		if (unlikely(leader->ptrace))
 			__wake_up_parent(leader, leader->parent);
 		write_unlock_irq(&tasklist_lock);
-		threadgroup_change_end(tsk);
+		cgroup_threadgroup_change_end(tsk);
 
 		release_task(leader);
 	}