Re: fork: mach_port_mod_refs: EKERN_UREFS_OWERFLOW

[Thomas Schwinge]

Hello!

On Tue, Nov 30, 2010 at 12:07:05PM +0100, I wrote:
> On Fri, Nov 26, 2010 at 01:22:05AM +0100, I wrote:
> > Should refs have simply been initialized to zero (as the zero value is
> > noneffective, and we'll set the ss->thread, etc. values later on)?
> 
> At the moment, I don't have the time to analyze this further, but I'll
> simply give this glibc code change a try, and re-run the GCC testsuite
> afterwards.

Hung again; at another position (understandably), but with the same
symptoms as before.  (I'm assuming that `fork' isn't linked into some
relevant binary statically, but as GDB shows the shared library's
version, I think I'm fine.)

Here is a program to make this same thing happen in 30 minutes instead of
the testsuite's one or two days.

    $ ./fork_forever
    [...]
    1817: 33
    1818: 37
    1819: 34
    1820: 35
    1821: 36
    1822: 38
    1823: 35
    1824: 36
    1825: 34
    1826: 37
    [hangs]

The GDB backtrace looks very much like the one on
<http://www.bddebian.com/~hurd-web/open_issues/fork_mach_port_mod_refs_ekern_urefs_owerflow/>.

Oh, and interesting piece of maths: 1826 * 35.5 (roughly) = 65536.  So I
guess that we're ``simply'' leaking something with every fork call...
I'll try to find some time to go hunting.


Regards,
 Thomas

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/wait.h>

int
main(int argc, char * argv[])
{
  pid_t child, pid;
  int status;
  time_t starttime, lasttime, nowtime;
  unsigned long int n_forks = 0;

  starttime = lasttime = time (NULL);

  while (1)
    {
      child = fork();
#define CHILD_EXIT 42
      if (child == -1)
        {
          perror("fork");
          exit(EXIT_FAILURE);
        }
      if (child == 0)
        _exit(CHILD_EXIT);
      pid = waitpid(child, &status, 0);
      if (pid == -1
          || !WIFEXITED(status)
          || WEXITSTATUS(status) != CHILD_EXIT)
        {
          perror("waitpid");
          exit(EXIT_FAILURE);
        }
      n_forks++;

      nowtime = time (NULL);
      if (lasttime != nowtime)
        {
          printf ("%u: %lu\n", (unsigned int) (nowtime - starttime), n_forks);
          n_forks = 0;
          lasttime = nowtime;
        }
    }

  return 0;
}

signature.asc
Description: Digital signature