Revert "sched: improve preempt debugging"

This reverts commit 7317d7b8.

This has been reported (and bisected) by Alexey Zaytsev and
Kamalesh Babulal to produce annoying warnings during bootup
on both x86 and powerpc.

kernel_locked() is not a valid test in IRQ context (we update the
BKL's ->lock_depth and the preempt count separately and non-atomicalyy),
so we cannot put it into the generic preempt debugging checks which
can run in IRQ contexts too.
Reported-and-bisected-by: NAlexey Zaytsev <alexey.zaytsev@gmail.com>
Reported-and-bisected-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -4440,7 +4440,7 @@ void __kprobes sub_preempt_count(int val)
 	/*
 	 * Underflow?
 	 */
-       if (DEBUG_LOCKS_WARN_ON(val > preempt_count() - (!!kernel_locked())))
+	if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
 		return;
 	/*
 	 * Is the spinlock portion underflowing?