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bpo-33613, test_semaphore_tracker_sigint: fix race condition (#7850)

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Fail `test_semaphore_tracker_sigint` if no warnings are expected and one is received.

Fix race condition when the child receives SIGINT before it can register signal handlers for it.

The race condition occurs when the parent calls
`_semaphore_tracker.ensure_running()` (which in turn spawns the
semaphore_tracker using `_posixsubprocess.fork_exec`), the child
registers the signal handlers and the parent tries to kill the child.
What seem to happen is that in some slow systems, the parent sends the
signal to kill the child before the child protects against the signal.
This commit is contained in:
Pablo Galindo 2018-09-04 09:53:54 +01:00 • committed by Antoine Pitrou
parent e9ba3705de
commit ec74d187f5
3 changed files with 52 additions and 12 deletions
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34
Lib/multiprocessing/semaphore_tracker.py
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@ -23,6 +23,9 @@ from . import util
__all__ = ['ensure_running', 'register', 'unregister']
_HAVE_SIGMASK = hasattr(signal, 'pthread_sigmask')
_IGNORED_SIGNALS = (signal.SIGINT, signal.SIGTERM)
class SemaphoreTracker(object):
@ -43,10 +46,16 @@ class SemaphoreTracker(object):
with self._lock:
if self._pid is not None:
# semaphore tracker was launched before, is it still running?
pid, status = os.waitpid(self._pid, os.WNOHANG)
if not pid:
# => still alive
return
try:
pid, _ = os.waitpid(self._pid, os.WNOHANG)
except ChildProcessError:
# The process terminated
pass
else:
if not pid:
# => still alive
return
# => dead, launch it again
os.close(self._fd)
self._fd = None
@ -68,7 +77,19 @@ class SemaphoreTracker(object):
exe = spawn.get_executable()
args = [exe] + util._args_from_interpreter_flags()
args += ['-c', cmd % r]
pid = util.spawnv_passfds(exe, args, fds_to_pass)
# bpo-33613: Register a signal mask that will block the signals.
# This signal mask will be inherited by the child that is going
# to be spawned and will protect the child from a race condition
# that can make the child die before it registers signal handlers
# for SIGINT and SIGTERM. The mask is unregistered after spawning
# the child.
try:
if _HAVE_SIGMASK:
signal.pthread_sigmask(signal.SIG_BLOCK, _IGNORED_SIGNALS)
pid = util.spawnv_passfds(exe, args, fds_to_pass)
finally:
if _HAVE_SIGMASK:
signal.pthread_sigmask(signal.SIG_UNBLOCK, _IGNORED_SIGNALS)
except:
os.close(w)
raise
@ -104,12 +125,13 @@ register = _semaphore_tracker.register
unregister = _semaphore_tracker.unregister
getfd = _semaphore_tracker.getfd
def main(fd):
'''Run semaphore tracker.'''
# protect the process from ^C and "killall python" etc
signal.signal(signal.SIGINT, signal.SIG_IGN)
signal.signal(signal.SIGTERM, signal.SIG_IGN)
if _HAVE_SIGMASK:
signal.pthread_sigmask(signal.SIG_UNBLOCK, _IGNORED_SIGNALS)
for f in (sys.stdin, sys.stdout):
try: