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From: Bhishan Hemrajani <bhishan@cytosine.dhs.org>
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Subject: Re: Code that crashes 3.4-Stable
In-Reply-To: <38c85e65.27328632@mail.afnetinc.com> from Elliot Finley at "Mar
 10, 2000 02:47:19 am"
To: lists@efinley.com
Date: Thu, 9 Mar 2000 18:51:38 -0800 (PST)
Cc: freebsd-questions@FreeBSD.ORG
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It does work when there are no limits on the users.

I recommend that everyone audits their users using /etc/login.conf.

I have my users limited to 32 processes, and 16m per process.

It didn't crash my system when I was logged in as a limited user.

--bhishan

P.S, after editing /etc/login.conf you have to 'cap_mkdb /etc/login.conf'


> I'm in the process of stress testing a system for a program that I'm
> writing.  This program will be starting lots of processes, so I wrote
> a short bit a code to test this out.
> 
> The machine is 3.4-stable as of a couple of days ago, PII-350 384M
> RAM, and 500M swap.  The kernel has MAXUSERS 512, which should give us
> about 8200 process slots.  After forking approx. 5100 children
> processes, the machine runs out of RAM, and starts using swap, after
> about 64K of swap is used (as shown by top), the machine freezes
> solid.  No core, no logged messages, no socket activity, no messages
> on console, nothing.
> 
> If someone can see a problem with the code, I would appreciate some
> pointers.  But even if there IS a problem...  You shouldn't be able to
> crash the system with a user program running with no privileges.
> 
> If I take out the 'sleep(30)' from the child process, then this
> program runs fine, even with the loop counter set to 100,000 (one
> hundred thousand), because the child processes go away fast enough
> that I can only get about 400 of them running at any one time.  The
> problem seems to be when the machine runs out of memory, and starts to
> swap.
> 
> Here is the code, it was compiled with 'g++ -o test test.c'
> -----------------------------------------------------------
> 
> #include <iostream.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <signal.h>
> #include <unistd.h>
> //#include <stdlib.h>
> 
> void sig_child(int i)
> {
>   int pid;
>   int status;
> 
>   while ( (pid = wait3(&status, WNOHANG, (struct rusage *) 0)) > 0) ;
> }
> 
> main()
> {
>   cout << "Hello World!" << endl;
> 
>   void sig_child(int i);
> 
>   signal(SIGCHLD, sig_child);
> 
>   int iIsParent;
> 
>   for(int i = 0; i < 8000; i++) {
>       iIsParent = fork();
>       if(iIsParent < 0) { cout << "Error Forking!" << endl; }
>       if(!iIsParent) {
>         cout << "I'm child #" << i << endl;
>         sleep(30);
>         return 0;
>       }
>   }
> 
>   sleep(10);
>   cout << "Parent done." << endl;
>   return 0;
> }
> 
> -- 
> Elliot (efinley@efinley.com) Weird Science!
> 
> 
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