x86/fpu: Move debugging check from kernel_fpu_begin() to __kernel_fpu_begin()

kernel_fpu_begin() is __kernel_fpu_begin() with a preempt_disable().

Move the kernel_fpu_begin() debugging check into __kernel_fpu_begin(),
so that users of __kernel_fpu_begin() may benefit from it as well.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
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/fpu/core.c

@@ -109,6 +109,8 @@ void __kernel_fpu_begin(void)
 {
 	struct fpu *fpu = &current->thread.fpu;
 
+	WARN_ON_ONCE(!irq_fpu_usable());
+
 	kernel_fpu_disable();
 
 	if (fpu->fpregs_active) {
@@ -138,7 +140,6 @@ EXPORT_SYMBOL(__kernel_fpu_end);
 void kernel_fpu_begin(void)
 {
 	preempt_disable();
-	WARN_ON_ONCE(!irq_fpu_usable());
 	__kernel_fpu_begin();
 }
 EXPORT_SYMBOL_GPL(kernel_fpu_begin);