Re: Bug in ulimit ?

[Stephane Chazelas <Stephane_Chazelas@yahoo.fr>]

On Tue, Apr 17, 2007 at 02:30:40AM -0700, Micah Cowan wrote:
> David Peer wrote:
> > If the user run: ulimit -t 0, he can run jobs without any cputime
> > limitation:
> 
> This sounds more like a kernel problem to me than a zsh bug. I get the
> same behavior on my Ubuntu 7.04 (beta) system, in _bash_.
> 
> I note that getrlimit(2) says:
> 
>  In 2.6.x kernels before 2.6.17, a RLIMIT_CPU  limit  of  0  is  wrongly
>  treated  as "no limit" (like RLIM_INFINITY).  Since kernel 2.6.17, set???
>  ting a limit of 0 does have an effect, but is  actually  treated  as  a
>  limit of 1 second.
> 
> However, I'm running 2.6.20(-14-generic), and still experiencing that
> symptom.
[...]

(note that there's a lot a modern CPU can do in 1 second).

Works as I'd expect from your man page quote here:

$ time zsh -c 'ulimit -t 0; while :; do :; done'
zsh: cpu limit exceeded  zsh -c 'ulimit -t 0; while :; do :; done'
zsh -c 'ulimit -t 0; while :; do :; done'  0.72s user 0.28s system 95% cpu 1.050 total
$ time bash -c 'ulimit -t 0; while :; do :; done'
zsh: killed     bash -c 'ulimit -t 0; while :; do :; done'
bash -c 'ulimit -t 0; while :; do :; done'  1.00s user 0.00s system 95% cpu 1.047 total
$ uname -a
Linux sc.homeunix.net 2.6.21-rc4 #1 PREEMPT Sun Mar 25 15:39:31 BST 2007 i686 GNU/Linux
~$ uname -rs
Linux 2.6.21-rc4


The abnormally high system time with zsh seems to be due to (according to
strace):

rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [CHLD], 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [CHLD], [CHLD], 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [CHLD], 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [CHLD], [CHLD], 8) = 0
[...]

-- 
Stéphane