MIPS: ptrace: Avoid smp_processor_id() when retrieving FPU IR

Whenever ptrace attempts to retrieve the FPU implementation register it
accesses it through current_cpu_data, which calls smp_processor_id().
Since the code may execute with preemption enabled, this can trigger
a warning. Fix this by using boot_cpu_data to get the IR instead.
Signed-off-by: NAlex Smith <alex@alex-smith.me.uk>
Cc: <stable@vger.kernel.org> # v3.15+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7449/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/ptrace.c

@@ -129,7 +129,7 @@ int ptrace_getfpregs(struct task_struct *child, __u32 __user *data)
 	}
 
 	__put_user(child->thread.fpu.fcr31, data + 64);
-	__put_user(current_cpu_data.fpu_id, data + 65);
+	__put_user(boot_cpu_data.fpu_id, data + 65);
 
 	return 0;
 }
@@ -480,7 +480,7 @@ long arch_ptrace(struct task_struct *child, long request,
 			break;
 		case FPC_EIR:
 			/* implementation / version register */
-			tmp = current_cpu_data.fpu_id;
+			tmp = boot_cpu_data.fpu_id;
 			break;
 		case DSP_BASE ... DSP_BASE + 5: {
 			dspreg_t *dregs;

arch/mips/kernel/ptrace32.c

@@ -129,7 +129,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 			break;
 		case FPC_EIR:
 			/* implementation / version register */
-			tmp = current_cpu_data.fpu_id;
+			tmp = boot_cpu_data.fpu_id;
 			break;
 		case DSP_BASE ... DSP_BASE + 5: {
 			dspreg_t *dregs;