[POWERPC] Enable interrupts if we are doing fp math emulation

Anytime we are emulating an instruction we are going to be doing some form of
get_user() to get the instruction image to decode.  Since get_user() might
sleep we need to ensure we have interrupts enabled or we might see something
like:

Debug: sleeping function called from invalid context at arch/powerpc/kernel/traps.c:697
in_atomic():0, irqs_disabled():1
Call Trace:
[D6023EB0] [C0007F84] show_stack+0x58/0x174 (unreliable)
[D6023EE0] [C0022C34] __might_sleep+0xbc/0xd0
[D6023EF0] [C000D158] program_check_exception+0x1d8/0x4fc
[D6023F40] [C000E744] ret_from_except_full+0x0/0x4c
--- Exception: 700 at 0x102a7100
    LR = 0xdb9ef04

However, we want to ensure that interrupts are disabled when handling a trap
exception that might be used for a kernel breakpoint.  This is why ProgramCheck
is marked as EXC_XFER_STD instead of EXC_XFER_EE.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/kernel/traps.c

@@ -739,20 +739,7 @@ void __kprobes program_check_exception(struct pt_regs *regs)
 	extern int do_mathemu(struct pt_regs *regs);
 
 	/* We can now get here via a FP Unavailable exception if the core
-	 * has no FPU, in that case no reason flags will be set */
-#ifdef CONFIG_MATH_EMULATION
-	/* (reason & REASON_ILLEGAL) would be the obvious thing here,
-	 * but there seems to be a hardware bug on the 405GP (RevD)
-	 * that means ESR is sometimes set incorrectly - either to
-	 * ESR_DST (!?) or 0.  In the process of chasing this with the
-	 * hardware people - not sure if it can happen on any illegal
-	 * instruction or only on FP instructions, whether there is a
-	 * pattern to occurences etc. -dgibson 31/Mar/2003 */
-	if (!(reason & REASON_TRAP) && do_mathemu(regs) == 0) {
-		emulate_single_step(regs);
-		return;
-	}
-#endif /* CONFIG_MATH_EMULATION */
+	 * has no FPU, in that case the reason flags will be 0 */
 
 	if (reason & REASON_FP) {
 		/* IEEE FP exception */
@@ -778,6 +765,20 @@ void __kprobes program_check_exception(struct pt_regs *regs)
 
 	local_irq_enable();
 
+#ifdef CONFIG_MATH_EMULATION
+	/* (reason & REASON_ILLEGAL) would be the obvious thing here,
+	 * but there seems to be a hardware bug on the 405GP (RevD)
+	 * that means ESR is sometimes set incorrectly - either to
+	 * ESR_DST (!?) or 0.  In the process of chasing this with the
+	 * hardware people - not sure if it can happen on any illegal
+	 * instruction or only on FP instructions, whether there is a
+	 * pattern to occurences etc. -dgibson 31/Mar/2003 */
+	if (do_mathemu(regs) == 0) {
+		emulate_single_step(regs);
+		return;
+	}
+#endif /* CONFIG_MATH_EMULATION */
+
 	/* Try to emulate it if we should. */
 	if (reason & (REASON_ILLEGAL | REASON_PRIVILEGED)) {
 		switch (emulate_instruction(regs)) {