Re: ntpd wedged by libc?

[Dave Hart <hart%ntp.org@localhost>]

On Tue, Mar 6, 2012 at 14:22, Christos Zoulas <christos%zoulas.com@localhost> 
wrote:
> On Mar 5,  8:03pm, agcarver+netbsd%acarver.net@localhost (AGC) wrote:
> | I had to bump it up to 30,000 but it finally did finish:
>
> Then I don't think it is leaking... You can try with the old libc,
> and you'll see it will run out of memory.

The problem has evolved.  At first, ntpd stopped responding due to out
of memory due to a leak triggered by lots of snprintf with floating
point.  With the leak so identified now fixed, it's still ntpd is now
reported to be "wedging" (I assume meaning spinning using lots of CPU
and not responding to network traffic) and it's still apparently
related to snprintf of floating points.  The opening message of this
thread has a stack trace which I assume came from attaching a debugger
to the spinning ntpd:

======
Seems I'm still having issues with libc on 5.1/sparc specifically with
ntpd wedging when doing math:

#0  0x103d38c8 in __pow5mult_D2A () from /usr/lib/libc.so.12
#1  0x103d3ac4 in __muldi3 () from /usr/lib/libc.so.12
#2  0x103d34dc in __mult_D2A () from /usr/lib/libc.so.12
#3  0x103d3728 in __pow5mult_D2A () from /usr/lib/libc.so.12
#4  0x103c61d4 in __dtoa () from /usr/lib/libc.so.12
#5  0x103c315c in __vfprintf_unlocked () from /usr/lib/libc.so.12
#6  0x103330c4 in snprintf () from /usr/lib/libc.so.12
#7  0x000256f4 in ctl_putdblf (tag=0x87d79 "", fmt=0x88458 "%.3f",
d=4.5623779296875)
   at ntp_control.c:1431
======

There have been over 50 messages in the thread, so I think we can all
be forgiven forgetting a detail or two along the way, but I don't
think anyone has suggested the original leak bug hasn't been fixed.
Rather, it seems there is still some sort of problem on "5.1" (not
-current, clearly) on sparc with ntpd being polled every few seconds
by ntpq triggering a hang snprintf'ing with floating point.

The stack trace looks very similar to the first go-around.  If
accurate, it suggests the same code still has issues that ntpd's abuse
tickles but t_printf.c doesn't.

Cheers,
Dave Hart