Date: Sat, 23 Dec 2006 00:45:57 -0600 From: "Scot Hetzel" <swhetzel@gmail.com> To: "M. Warner Losh" <imp@bsdimp.com> Cc: youshi10@u.washington.edu, freebsd-current@freebsd.org Subject: Re: settimeofday function taking 24 - 30 minutes to complete Message-ID: <790a9fff0612222245n70994662y49aebed77c8eb45b@mail.gmail.com> In-Reply-To: <20061220.185514.-345500127.imp@bsdimp.com> References: <45887A31.4050801@paradise.net.nz> <790a9fff0612191741r656fbbe0ic8660a9c59ba632b@mail.gmail.com> <45889598.3030408@u.washington.edu> <20061220.185514.-345500127.imp@bsdimp.com>
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On 12/20/06, M. Warner Losh <imp@bsdimp.com> wrote:
> It does run almost instantly if you use a time from 2000. The date
> command also causes the lockup if you say 'date 1970010100140' as
> well. Looks like there's a loop in the kernel to do division, but I
> can't quite find where it is.
>
> If you have a good test setup, maybe you can do a binary search in the
> settimeofday code to find why a large leap backwards causes problems.
>
Found the source of the problem by following the code in
kern_settimeofday (sys/kern/kern_time.c), settime
(sys/kern/kern_time.c), and finally in resettodr
(sys/amd64/isa/clock.c).
/*
* Write system time back to RTC
*/
void
resettodr()
{
:
s = splclock();
tm = time_second;
splx(s);
:
/* Calculate local time to put in RTC */
tm -= utc_offset();
:
/* We have now the days since 01-01-1970 in tm */
writertc(RTC_WDAY, (tm + 4) % 7 + 1); /* Write back Weekday */
for (y = 1970, m = DAYSPERYEAR + LEAPYEAR(y);
tm >= m;
y++, m = DAYSPERYEAR + LEAPYEAR(y))
tm -= m;
:
}
After adding some printf's to the resettodor, I was able to get some
interesting results:
hp010# ./t1
INFO: test running as root
INFO: Saved current time
settime: delta.tv_sec = - 1166842289
resettodr: tm = 100
resettodr: tm = -21500, utc_offset = 21600 <- value after subtracting
utc_offset()
resettodr: tm= 229, y = 426495804 <- the hang occurs in the
calculation for year.
INFO: settimeofday completed successfully
settime: delta.tv_sec = 1166840819
resettodr: tm = 1166842388
resettodr: tm = 1166820788
resettodr: tm = 355, y = 2006
INFO: Reset time to original value
By making the following change, the test program no longer hangs the system:
/*
* Calculate local time to put in RTC
* Ignore UTC offset, if it would cause the time < Jan 1, 1970 00:00.
*/
if (tm >= utc_offset())
tm -= utc_offset();
else
printf("resettodr: utc_offset > tm");
We probably need to change all the locations that use utc_offset(), to
have a similar "if (x >= utc_offset()) x -= utc_offset();".
Scot
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