do_posix_clock_monotonic_gettime() returns negative nsec

[Herbert Poetzl]

Hi Folks!

recent kernels (tested 2.6.10-rc2 and 2.6.10-rc2-bk15)
produce funny output in /proc/uptime like this:

	# cat /proc/uptime
	  12.4294967218 9.05
	# cat /proc/uptime
	  13.4294967251 10.33
	# cat /proc/uptime
	  14.4294967295 11.73

a short investigation of the issue, ended at
do_posix_clock_monotonic_gettime() which can (and 
often does) return negative nsec values (within
one second), so while the actual 'time' returned
is correct, some parts of the kernel assume that
those part is within the range (0 - NSEC_PER_SEC)

        len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
                        (unsigned long) uptime.tv_sec,
                        (uptime.tv_nsec / (NSEC_PER_SEC / 100)),

as the function itself corrects overflows, it would
make sense to me to correct underflows too, for 
example with the following patch:

--- ./kernel/posix-timers.c.orig	2004-11-19 21:11:05.000000000 +0100
+++ ./kernel/posix-timers.c	2004-12-03 02:23:56.000000000 +0100
@@ -1208,7 +1208,10 @@ int do_posix_clock_monotonic_gettime(str
 	tp->tv_sec += wall_to_mono.tv_sec;
 	tp->tv_nsec += wall_to_mono.tv_nsec;
 
-	if ((tp->tv_nsec - NSEC_PER_SEC) > 0) {
+	if (tp->tv_nsec < 0) {
+		tp->tv_nsec += NSEC_PER_SEC;
+		tp->tv_sec--;
+	} else if ((tp->tv_nsec - NSEC_PER_SEC) > 0) {
 		tp->tv_nsec -= NSEC_PER_SEC;
 		tp->tv_sec++;
 	}

best,
Herbert

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/