Fix idle time field in /proc/uptime

commit 96830a57 upstream.

Git commit 79741dd3 changes idle cputime accounting, but unfortunately
the /proc/uptime file hasn't caught up.  Here the idle time calculation
from /proc/stat is copied over.
Signed-off-by: Michael Abbott <michael.abbott@diamond.ac.uk>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/proc/uptime.c

@@ -4,13 +4,18 @@
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/time.h>
+#include <linux/kernel_stat.h>
 #include <asm/cputime.h>
 
 static int uptime_proc_show(struct seq_file *m, void *v)
 {
 	struct timespec uptime;
 	struct timespec idle;
-	cputime_t idletime = cputime_add(init_task.utime, init_task.stime);
+	int i;
+	cputime_t idletime = cputime_zero;
+
+	for_each_possible_cpu(i)
+		idletime = cputime64_add(idletime, kstat_cpu(i).cpustat.idle);
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	monotonic_to_bootbased(&uptime);