Message-ID: <40C1E6A9.3010307@elegant-software.com>
Date: Sat, 05 Jun 2004 11:28:41 -0400
From: Russell Leighton <russ@elegant-software.com>
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To: linux-kernel@vger.kernel.org
Subject: clone() <-> getpid() bug in 2.6?
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I have a test program (see attached) that shows what looks like a bug in 
2.6.5-1.358 (FedoraCore2)...and breaks my program :(

In summary, I am doing:

 clone(run_thread, stack + sizeof(stack) -1,
            CLONE_FS|CLONE_FILES|CLONE_VM|SIGCHLD, NULL))

According to the man page the child process should have its own pid as 
returned by getpid()...much like fork().

In 2.6 the child receives the parent's pid from getpid(), while 2.4 
works as documented:

In 2.4 the test program does:
 parent pid: 26647
 clone returned pid: 26648
 thread reported pid: 26648

In 2.6 the test program does:
 parent pid: 16665
 thread reported pid: 16665
 clone returned pid: 16666

Is this fixed in later kernels?

Thx

Russ

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

/* to compile:
  gcc -Wall clone-pid-test.c -o clone-pid-test
 */

static int run_thread(void *arg)
{
  printf("thread reported pid: %d\n", getpid()); 

  return 0;
}

static char stack[4096];

static int create_thread()
{
  int
    pid;

  /* create thread */
  if ( (pid = clone(run_thread, stack + sizeof(stack) -1,
		    CLONE_FS|CLONE_FILES|CLONE_VM|SIGCHLD, NULL)) == -1 ) {
    perror("clone:");
    exit(-1);
  }/* end if */

  return pid ;
}

int main(int argc, char *argv[])
{
  printf("parent pid: %d\n", getpid());
  printf("clone returned pid: %d\n",  create_thread());
  wait(NULL);
  return 0;
}

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