Messages in this thread | | | Date | Fri, 03 Dec 2004 00:43:53 -0800 | From | George Anzinger <> | Subject | Re: do_posix_clock_monotonic_gettime() returns negative nsec |
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john stultz wrote: > On Thu, 2004-12-02 at 18:03, Herbert Poetzl wrote: > >>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++; >> } > > > Sounds like its a good fix to me. > > George: You have any comment?
Two, in fact. First, the result here is the sum of wall_to_monotonic and getnstimeofday(). If nsec < 0, one or more of these must be also. Both of these values are SUPPOSED to be normalized.
Second, I would rather see: set_normalized_timespec(tp, tp->tv_sec + wall_to_mono.tv_sec, tp->tv_nsec + wall_to_mono.tv_nsec);
Still, doing this paves over the first issue....
> > thanks > -john > >
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/
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