Messages in this thread Patch in this message | | | Date | Fri, 3 Dec 2004 03:03:58 +0100 | From | Herbert Poetzl <> | Subject | do_posix_clock_monotonic_gettime() returns negative nsec |
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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
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