x86: cpuid: propagate error from smp_call_function_single()

Propagate error (-ENXIO) from smp_call_function_single() in the CPUID
driver.  This can happen when a CPU is unplugged while the CPUID
driver is open.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/cpuid.c

@@ -89,6 +89,7 @@ static ssize_t cpuid_read(struct file *file, char __user *buf,
 	struct cpuid_regs cmd;
 	int cpu = iminor(file->f_path.dentry->d_inode);
 	u64 pos = *ppos;
+	int err;
 
 	if (count % 16)
 		return -EINVAL;	/* Invalid chunk size */
@@ -96,7 +97,9 @@ static ssize_t cpuid_read(struct file *file, char __user *buf,
 	for (; count; count -= 16) {
 		cmd.eax = pos;
 		cmd.ecx = pos >> 32;
-		smp_call_function_single(cpu, cpuid_smp_cpuid, &cmd, 1);
+		err = smp_call_function_single(cpu, cpuid_smp_cpuid, &cmd, 1);
+		if (err)
+			return err;
 		if (copy_to_user(tmp, &cmd, 16))
 			return -EFAULT;
 		tmp += 16;