Package: libc6-dev
Version: 2.24-9
Severity: grave
Dear Maintainer,
the program below shows the problem, happening on my Debian laptop.
When I create a child using clone(CLONE_VM), glibc's clone wrapper
does not update cached pid, and I receive parent's pid in getpid().
Here is output of the program:
$strace -o strace.log -f ./a.out
parent: pid=17530
parent: fork pid=17531
1)child: pid=17531
2)child: pid=17530
When CLONE_VM flag is not passed, the problem does not occur.
My case is not in the list of the cases, described in clone(2),
when wrong pid may be returned, so this is a BUG.
Regards,
Kirill
P.S. Strange, but reportbug-ng did not fill packages versions. So,
I do this manually:
$ dpkg-query -l 'libc6*'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture
Description
+++-=============================-===================-===================-================================================================
ii libc6:amd64 2.24-9 amd64 GNU C
Library: Shared libraries
ii libc6:i386 2.24-9 i386 GNU C
Library: Shared libraries
ii libc6-amd64:i386 2.24-9 i386 GNU C
Library: 64bit Shared libraries for AMD64
ii libc6-arm64-cross 2.24-9cross3 all GNU C
Library: Shared libraries (for cross-compiling)
un libc6-arm64-dcv1 <none> <none> (no
description available)
ii libc6-dbg:amd64 2.24-9 amd64 GNU C
Library: detached debugging symbols
ii libc6-dev:amd64 2.24-9 amd64 GNU C
Library: Development Libraries and Header Files
ii libc6-dev-arm64-cross 2.24-9cross3 all GNU C
Library: Development Libraries and Header Files (for cross
un libc6-dev-arm64-dcv1 <none> <none> (no
description available)
ii libc6-dev-i386 2.24-9 amd64 GNU C
Library: 32-bit development libraries for AMD64
ii libc6-dev-x32 2.24-9 amd64 GNU C
Library: X32 ABI Development Libraries for AMD64
ii libc6-i386 2.24-9 amd64 GNU C
Library: 32-bit shared libraries for AMD64
un libc6-i686 <none> <none> (no
description available)
ii libc6-x32 2.24-9 amd64 GNU C
Library: X32 ABI Shared libraries for AMD64
un libc6.1 <none> <none> (no
description available)
un libc6.1-dev <none> <none> (no
description available)
un libc6.1-dev-arm64-cross <none> <none> (no
description available)
#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>
int child(void *a)
{
printf("1)child: pid=%d\n", syscall(__NR_getpid));
printf("2)child: pid=%d\n", getpid());
return 0;
}
int main(void)
{
int stack_size = 2 * 1024 * 1024;
char *stack = mmap(NULL, stack_size, PROT_WRITE | PROT_READ,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
pid_t pid;
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);
}
--- System information. ---
Architecture:
Kernel: Linux 4.10.1+
Debian Release: 9.0
500 unstable ftp.ru.debian.org
500 testing ftp.ru.debian.org
500 stable-updates ftp.ru.debian.org
500 stable security.debian.org
500 stable ftp.ru.debian.org
1 experimental ftp.ru.debian.org
--- Package information. ---
Depends (Version) | Installed
===============================-+-=============
libc6 (= 2.24-9) |
libc-dev-bin (= 2.24-9) |
linux-libc-dev (>= 4.9.2-2) |
Package's Recommends field is empty.
Suggests (Version) | Installed
===========================-+-===========
glibc-doc |
manpages-dev | 4.09-2
17530 execve("./a.out", ["./a.out"], [/* 48 vars */]) = 0
17530 brk(NULL) = 0x123e000
17530 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
17530 mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb686e47000
17530 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
17530 open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
17530 fstat(3, {st_mode=S_IFREG|0644, st_size=190344, ...}) = 0
17530 mmap(NULL, 190344, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fb686e18000
17530 close(3) = 0
17530 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
17530 open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
17530 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\3\2\0\0\0\0\0"..., 832) = 832
17530 fstat(3, {st_mode=S_IFREG|0755, st_size=1685264, ...}) = 0
17530 mmap(NULL, 3791264, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fb686889000
17530 mprotect(0x7fb686a1e000, 2093056, PROT_NONE) = 0
17530 mmap(0x7fb686c1d000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x194000) = 0x7fb686c1d000
17530 mmap(0x7fb686c23000, 14752, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fb686c23000
17530 close(3) = 0
17530 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb686e16000
17530 arch_prctl(ARCH_SET_FS, 0x7fb686e16700) = 0
17530 mprotect(0x7fb686c1d000, 16384, PROT_READ) = 0
17530 mprotect(0x600000, 4096, PROT_READ) = 0
17530 mprotect(0x7fb686e4a000, 4096, PROT_READ) = 0
17530 munmap(0x7fb686e18000, 190344) = 0
17530 mmap(NULL, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb686689000
17530 getpid() = 17530
17530 write(1, "parent: pid=17530\n", 18) = 18
17530 clone(child_stack=0x7fb686888ff0, flags=CLONE_VM|CLONE_FILES|SIGCHLD) = 17531
17531 getpid( <unfinished ...>
17530 write(1, "parent: fork pid=17531\n", 23 <unfinished ...>
17531 <... getpid resumed> ) = 17531
17530 <... write resumed> ) = 23
17530 exit_group(0) = ?
17531 write(1, "1)child: pid=17531\n", 19 <unfinished ...>
17530 +++ exited with 0 +++
17531 <... write resumed> ) = 19
17531 write(1, "2)child: pid=17530\n", 19) = 19
17531 exit_group(0) = ?
17531 +++ exited with 0 +++
