Description of problem:

When a child process is created by clone(CLONE_VM), getpid() returns a parent PID. This problem exists in fc25 (glibc-2.24-4.fc25.x86_64) and doesn't exist in fc24 (glibc-2.23.1-11.fc24.x86_64).

[avagin@laptop ~]$ cat test1.c 
#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <signal.h>
#include <sys/wait.h>

int child(void *a)
{
	printf("1)child: pid=%ld\n", syscall(__NR_getpid));
	printf("2)child: pid=%d\n", getpid());
	if (getpid() != syscall(__NR_getpid))
		printf("FAIL\n");
	return 0;
}

int main(void)
{
	int stack_size = 2 * 1024 * 1024, status;
	char *stack;
	pid_t pid;

	stack = mmap(NULL, stack_size, PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
	if (stack == MAP_FAILED) {
		perror("Can't allocate stack");
		exit(1);
	}

	setbuf(stdout, NULL);

	printf("parent: pid=%d\n", getpid());
	pid = clone(child, stack + stack_size, CLONE_VM | CLONE_FILES | SIGCHLD, NULL);
	printf("parent: fork pid=%d\n", pid);
	waitpid(pid, &status, 0);
}

[avagin@laptop ~]$ rpm -q glibc
glibc-2.24-4.fc25.x86_64
glibc-2.24-4.fc25.i686
[avagin@laptop ~]$ gcc -Wall test1.c 
[avagin@laptop ~]$ ./a.out 
parent: pid=8301
parent: fork pid=8302
1)child: pid=8302
2)child: pid=8301
FAIL

[root@fc24 ~]# rpm -q glibc
glibc-2.23.1-11.fc24.x86_64
glibc-2.23.1-11.fc24.i686
[root@fc24 ~]# gcc -Wall test1.c 
[root@fc24 ~]# ./a.out 
parent: pid=10453
parent: fork pid=10454
1)child: pid=10454
2)child: pid=10454


Version-Release number of selected component (if applicable):
glibc-2.24-4.fc25.x86_64

How reproducible:
100%


Steps to Reproduce:
1. Compile the previous program
2. Check that getpid() and syscall(__NR_getpid) return the same values for a child process

Actual results:
getpid() returns a parent PID

Expected results:
getpid() returns a child PID