mutini: handle possible missed zombie cleanup

Rather than reaping on SIGCHLD, use a poll() with a timeout that will
check for zombies, the poll() exits on SIGCHLD and also on timeout. This
seems to catch the case we had before were we missed cleaning up a
zombie

Also we avoid logging in the signal handler which was causing an
exception.

Signed-off-by: Christian Hopps <[email protected]>

munet/mutini.py

@@ -15,6 +15,7 @@
 import logging
 import os
 import re
+import select
 import shlex
 import signal
 import subprocess
@@ -119,9 +120,15 @@ def exit_with_status(status):
  sys.exit(ec)
 
 
-def waitpid(tag):
- logging.debug("%s: waitid for exiting process", tag)
- idobj = os.waitid(os.P_ALL, 0, os.WEXITED)
+def __waitpid(tag, nohang=False): # pylint: disable=inconsistent-return-statements
+ if nohang:
+ idobj = os.waitid(os.P_ALL, 0, os.WEXITED | os.WNOHANG)
+ if idobj is None:
+ return True
+ else:
+ idobj = os.waitid(os.P_ALL, 0, os.WEXITED)
+ assert idobj is not None
+
  pid = idobj.si_pid
  status = idobj.si_status
 
@@ -130,13 +137,23 @@ def waitpid(tag):
  logging.debug(
  "%s: reaped zombie %s (%s) w/ status %s", tag, pid, pidname, status
  )
- return
+ return False
 
  logging.debug("reaped child with status %s", status)
  exit_with_status(status)
  # NOTREACHED
 
 
+def waitpid(tag):
+ logging.debug("%s: waitid for exiting process", tag)
+ __waitpid(tag, False)
+
+ while True:
+ logging.debug("%s: checking for another exiting process", tag)
+ if __waitpid(tag, True):
+ return
+
+
 def sig_trasmit(signum, _):
  signame = signal.Signals(signum).name
  if g.child_pid == -1:
@@ -158,10 +175,6 @@ def sig_trasmit(signum, _):
 
 def sig_sigchld(signum, _):
  assert signum == S.SIGCHLD
- try:
- waitpid("SIGCHLD")
- except ChildProcessError as error:
- logging.warning("got SIGCHLD but no pid to wait on: %s", error)
 
 
 def setup_init_signals():
@@ -250,6 +263,19 @@ def is_creating_pid_namespace():
  return p1name != p2name
 
 
+def poll_for_pids(msg, tag):
+ poller = select.poll()
+ while True:
+ logging.info("%s", msg)
+ events = poller.poll(1000)
+ logging.info("init: poll: checking for zombies and child exit: %s", events)
+ try:
+ waitpid(tag)
+ except ChildProcessError as error:
+ logging.warning("init: got SIGCHLD but no pid to wait on: %s", error)
+ # NOTREACHED
+
+
 def be_init(new_pg, exec_args):
  #
  # Arrange for us to be killed when our parent dies, this will subsequently also kill
@@ -299,10 +325,7 @@ def be_init(new_pg, exec_args):
  # Reap children as init process
  vdebug("installing local handler for SIGCHLD")
  signal.signal(signal.SIGCHLD, sig_sigchld)
-
- while True:
- logging.info("init: waiting to reap zombies")
- linux.pause()
+ poll_for_pids("init: waiting to reap zombies", "PAUSE-EXIT")
  # NOTREACHED
 
  # Set (parent) signal handlers before any fork to avoid race
@@ -321,9 +344,8 @@ def be_init(new_pg, exec_args):
  os.execvp(exec_args[0], exec_args)
  # NOTREACHED
 
- while True:
- logging.info("parent: waiting for child pid %s to exit", g.child_pid)
- waitpid("parent")
+ poll_for_pids(f"parent: waiting for child pid {g.child_pid} to exit", "PARENT")
+ # NOTREACHED
 
 
 def unshare(flags):
@@ -411,9 +433,7 @@ def main():
 
  if g.orig_pid != 1 and not new_pid:
  # Simply hold the namespaces
- while True:
- logging.info("holding namespace waiting to be signaled to exit")
- linux.pause()
+ poll_for_pids("holding namespace waiting to be signaled to exit", "PARENT")
  # NOTREACHED
 
  be_init(not args.no_proc_group, args.rest)