[1.6.4][libs/zbxsysinfo] about parent process behavior when fork() failed

[t2y]

Hi

PANDA and I have a question about calling fork() action.
Target function is RUN_COMMAND() in "src/libs/zbxsysinfo/common/common.c".
That's as follows code.

This code means 3 processes exist normally.
I named them PARENT, CHILD and GRAND-CHILD.
At line 417-419, we suspect strange behavior is returning "SYSINFO_RET_FAIL" if "fork2" failed.
Because, we suspect the PARENT keep to wait at line 443.
However, it may run normally instead of PARENT after CHILD was returned.
I think the best way is exiting waited original PARENT process.
What do you think?

407  pid = zbx_fork(); /* run new thread 1 */
408  switch(pid)
409  {
410  case -1:
411          zabbix_log(LOG_LEVEL_WARNING, "fork failed for command '%s'",command);
412          return SYSINFO_RET_FAIL;
413  case 0:
414          pid = zbx_fork(); /* run new tread 2 to replace by command */
415          switch(pid)
416          {
417          case -1:
418                  zabbix_log(LOG_LEVEL_WARNING, "fork2 failed for '%s'",command);
419                  return SYSINFO_RET_FAIL;
420          case 0:
421                  /*
422                   * DON'T REMOVE SLEEP
423                   * sleep needed to return server result as "1"
424                   * then we can run "execl"
425                   * otherwise command print result into socket with STDOUT id
426                   */
427                  sleep(3);
428                  /**/
429
430                  /* replace thread 2 by the execution of command */
431                  if(execl("/bin/sh", "sh", "-c", command, (char *)0))
432                  {
433                          zabbix_log(LOG_LEVEL_WARNING, "execl failed for command '%s'",command);
434                  }
435                  /* In normal case the program will never reach this point */
436                  exit(0);
437          default:
438                  waitpid(pid, NULL, WNOHANG); /* NO WAIT can be used for thread 2 closing */
439                  exit(0); /* close thread 1 and transmit thread 2 to system (solve zombie state) */
440                  break;
441          }
442  default:
443          waitpid(pid, NULL, 0); /* wait thread 1 closing */
444          break;
445  }

I made sample code(named t2y_fork.c) verifying this problem. That's the result.

$ gcc -g -Wall t2y_fork.c
$ ./a.out
-- start fork
@ I am child,  pid is 1199, ppid is 1198
# I am parent, pid is 1198, ppid is 2836
fork: Success
^C
You have to Ctrl-C to stop.

[richlv]

i don't code and i didn't understand what this is about, but if you feel that is a correct way for something, maybe it's worth submitting on the tracker

[t2y]

Hi richlv,

Sorry for my poor explanation.
I think this is a kind of memory leak problem, because PARENT process keep to wait in certain state. However, I'm not sure how to fix this problem.