Most recent kernel where this bug did not occur: unknown
Distribution: PLD Linux
Hardware Environment: i686
Software Environment: glibc-2.6.1 (NPTL)
Problem Description: Calling setpgid on a child process by a thread other than the main thread fails with ESRCH.

Steps to reproduce:

#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <stdio.h>

void *thread_body(void *arg) {
   pid_t pid;
   int status;
   (void)arg;
   pid = fork();
   if (pid == 0) {
      sleep(1);
      exit(0);
   }
   if (setpgid(pid, 0) == -1)
      perror("setpgid");
   else
      printf("ok\n");
   return NULL;
}

int main(void) {
   pthread_t th;
   printf("From the main thread\n");
   thread_body(NULL);
   printf("From another thread\n");
   pthread_create(&th, NULL, thread_body, NULL);
   pthread_join(th, NULL);
   return 0;
}

Actual result:

From the main thread
ok
From another thread
setpgid: No such process

Expected result:

From the main thread
ok
From another thread
ok