Date: Fri, 21 Aug 1998 19:49:34 -0400 (EDT) From: Brian Feldman <green@unixhelp.org> To: Stefan Eggers <seggers@semyam.dinoco.de> Cc: freebsd-current@FreeBSD.ORG Subject: Re: 13 months of user time? Message-ID: <Pine.BSF.4.02.9808211944040.23238-100000@zone.syracuse.net> In-Reply-To: <199808210836.KAA02477@semyam.dinoco.de>
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Argh, you're right, I entirely forgot about having to handle the
microsecond counter, that it's not like seconds since the epoch, and rolls
over all the time ;) But in all these cases, it's a BIG change, so tv_usec
shouldn't matter at all anyway, so the following should do:
if (switchtime.tv_sec < p->p_switchtime.tv_sec)
panic("%s at line %d: time check failed, time going backwards",
__FILE__, __LINE__);
Cheers,
Brian Feldman
On Fri, 21 Aug 1998, Stefan Eggers wrote:
> > SIGXCPU kill problem could try putting the following in kern/kern_synch.c
> > line 638:
>
> I think better not this one as that is a safe way to a panic IMHO. A
> version I think does what you intend this to do I add below. It is
> untested code I just added while writing the mail.
>
> > if (switchtime.tv_usec < p->p_switchtime.tv_usec ||
> > switchtime.tv_sec < p->p_switchtime.tv_sec)
> > panic("bogus microuptime twiddling");
> >
> > And see if we get some nice panics and cores. Is it worth a shot? I've
>
> As far as I can see the timeval in the process structure is a real
> timeval and not abused to be something else. So tv_usec contains the
> micro seconds part and tv_sec the seconds.
>
> Let's assume that p->p_switchtime.tv_usec contains 999999 now and
> p->p_switchtime.tv_sec is 0. Lets suppose the time continues a little
> bit and when we reach the if statement switchtime.tv_usec might
> contain 0 and switchtime.tv_sec 1. The time didn't go backward but
> with the code above causes a panic.
>
> > never gotten a SIGXCPU out of place, so my machine wouldn't be the one to
> > test this on.
>
> And I don't think you want the test this way, anyway. ;-)
>
> One has first to calculate a 64 bit integer from the seconds and micro
> seconds and then compare the two resulting numbers. With that it
> could actually detect switchtime going backward.
>
> Something like this:
>
> int64_t time1, time2;
> [...]
> time1 = switchtime.tv_usec + switchtime.tv_sec * (int64_t)1000000;
> time2 = p->p_switchtime.tv_usec + p->p_switchtime.tv_sec * (int64_t)1000000;
> if (time1 < time2)
> panic("Ooops! Switchtime going backward!");
>
> Stefan.
> --
> Stefan Eggers Lu4 yao2 zhi1 ma3 li4,
> Max-Slevogt-Str. 1 ri4 jiu3 jian4 ren2 xin1.
> 51109 Koeln
> Federal Republic of Germany
>
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