Re: Bug in ulimit ?

[David Peer <davidpeer@xxxxxxxxxxxxx>]

I forgot:

The file that needs to be changed, of-course is: kernel/sys.c

It was check on kernel 2.6.20.3


David

David Peer wrote:

> I hope kernel people will add it to the next kernel release,
>
> but here is one rapid fix that solves the problem.
>
> (you will not see the new limit of 1 sec but you'll still see it set 
> to 0, but its 1 sec - believe me && try,
>
> if you want to see it, fork another any shell and you'll see it....bug 
> or feature?!)
>
>
> Before the line: *old_rlim = new_rlim;
>
>
> add:
>
>
> if (resource == RLIMIT_CPU && new_rlim.rlim_cur == 0) {
>            /*
>             * The caller is asking for an immediate RLIMIT_CPU
>             * expiry.  But we use the zero value to mean "it was
>             * never set".  So let's cheat and make it one second
>             * instead
>             */
>            new_rlim.rlim_cur = 1;
>        }
>
>
> You can remove the dumb if statement that does nothing cause the 
> assignment occurs(*old_rlim = new_rlim) before
>
> so it has no meaning! : if (rlim_cur == 0) {....}
>
>
> David
>
>
>
> Stephane Chazelas wrote:
>
> > On Tue, Apr 17, 2007 at 02:24:46PM +0100, Stephane Chazelas wrote:
> >  
> > > On Tue, Apr 17, 2007 at 02:03:16PM +0100, Stephane Chazelas wrote:
> > > [...]
> > >    
> > > > So it would seem that the limit is inherited but not applied in
> > > > the child (and I couldn't see any signal being blocked or
> > > > ignored). So that's probably not a libc issue, rather a Linux
> > > > issue.
> > > >       
> > > [...]
> > >     
> >
> > Please ignore this email, I was talking rubbish again, I should
> > probably get back to sleep....
> >
> >  
> > > The Linux code for setrlimit gives a hint:
> > >
> > >         if (it_prof_secs == 0 || new_rlim.rlim_cur <= it_prof_secs) {
> > >                 unsigned long rlim_cur = new_rlim.rlim_cur;
> > >                 cputime_t cputime;
> > >
> > >                 if (rlim_cur == 0) {
> > >                         /*
> > >                          * The caller is asking for an immediate 
> > > RLIMIT_CPU
> > >                          * expiry.  But we use the zero value to 
> > > mean "it was
> > >                          * never set".  So let's cheat and make it 
> > > one second
> > >                          * instead
> > >                          */
> > >                         rlim_cur = 1;
> > >                 }
> > >
> > > It's stored as being "0" and armed with a 1 second delay. And on a 
> > > fork,
> > > obviously, for the new process, there's no way to distinguish
> > > between a 0 that means "not set" and a 0 that means exit
> > > immediately.
> > >
> > > And one can verify that it_prof_expires will be set to 0 in
> > > copy_signal during the fork and that 0 means not armed in
> > > check_process_timers.
> > >
> > > But what's the point of setting a cputime of 0 anyway?
> > >     
> >
> >   


--
David Peer <!> davidpeer@xxxxxxxxxxxxx
CS System Group | Phone: 02 - 6586942
School of Computer Science and Engineering
Hebrew University of Jerusalem - Israel
Edmund Safra Campus - Givat Ram