x86/fpu: Simplify fpu__unlazy_stopped()

Open code the PF_USED_MATH logic, to make the logic more obvious.

(We'll slowly convert the other users of *_used_math() methods as well.)
Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/i387.c

@@ -290,7 +290,7 @@ static int fpu__unlazy_stopped(struct task_struct *child)
 	if (WARN_ON_ONCE(child == current))
 		return -EINVAL;
 
-	if (tsk_used_math(child)) {
+	if (child->flags & PF_USED_MATH) {
 		task_disable_lazy_fpu_restore(child);
 		return 0;
 	}
@@ -304,7 +304,9 @@ static int fpu__unlazy_stopped(struct task_struct *child)
 
 	fpu_finit(&child->thread.fpu);
 
-	set_stopped_child_used_math(child);
+	/* Safe to do for stopped child tasks: */
+	child->flags |= PF_USED_MATH;
+
 	return 0;
 }