Bug#599361: python2.6: please reset SIGCHLD to SIG_DFL at start

[Jakub Wilk]

Package: python2.6
Version: 2.6.6-5
Severity: minor

According to POSIX, “If the SIGCHLD signal is set to be ignored by the calling
process image, it is unspecified whether [after an exec*() call] the SIGCHLD
signal is set to be ignored or to the default action in the new process
image.”[0] In fact, SIGCHLD->SIG_IGN is inherited by child processes on Linux



I attach a simple program to expose the current buggy behavior:

$ python test-sigchld.py SIG_DFL
Hello world!

$ python test-sigchld.py SIG_IGN
Hello world!
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.6/subprocess.py", line 470, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/usr/lib/python2.6/subprocess.py", line 1182, in wait
    pid, sts = _eintr_retry_call(os.waitpid, self.pid, 0)
  File "/usr/lib/python2.6/subprocess.py", line 455, in _eintr_retry_call
    return func(*args)
OSError: [Errno 10] No child processes


[0] http://www.opengroup.org/onlinepubs/009695399/functions/exec.html

-- System Information:
Debian Release: squeeze/sid
   APT prefers unstable
   APT policy: (990, 'unstable'), (500, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 2.6.32-5-686 (SMP w/1 CPU core)
Locale: LANG=C, LC_CTYPE=pl_PL.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages python2.6 depends on:
ii  libbz2-1.0                1.0.5-6        high-quality block-sorting file co
ii  libc6                     2.11.2-6       Embedded GNU C Library: Shared lib
ii  libdb4.8                  4.8.30-2       Berkeley v4.8 Database Libraries [
ii  libexpat1                 2.0.1-7        XML parsing C library - runtime li
ii  libncursesw5              5.7+20100313-4 shared libraries for terminal hand
ii  libreadline6              6.1-3          GNU readline and history libraries
ii  libsqlite3-0              3.7.2-1        SQLite 3 shared library
ii  mime-support              3.48-1         MIME files 'mime.types' & 'mailcap
ii  python2.6-minimal         2.6.6-5        A minimal subset of the Python lan

--
Jakub Wilk

#!/usr/bin/python
import os
import sys
import signal

actions = 'SIG_DFL', 'SIG_IGN'

if len(sys.argv) != 2 or sys.argv[1] not in actions:
    print >>sys.stderr, '%s {%s}' % (sys.argv[0], '|'.join(actions))
    sys.exit(1)

action = sys.argv[1]
signal.signal(signal.SIGCHLD, getattr(signal, action))
os.execv('/usr/bin/python', [
    'python', '-c',
    "import subprocess; subprocess.call('echo Hello world!', shell=True)"
])

# vim:ts=4 sw=4 et

and Hurd systems (though, apparently, not on kFreeBSD). However, the subprocess module and (possibly) other process spawning functions are broken if SIGCHLD is set to SIG_IGN. Therefore, the interpreter should reset SIGCHLD to a sane value (i.e. SIG_DFL) at start.

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