From 928bcb10a46939eaf801bea0b633e4624b5b5dfa Mon Sep 17 00:00:00 2001 From: Richard Purdie Date: Tue, 29 Mar 2022 15:17:10 +0100 Subject: bitbake: cooker/process: Fix signal handling lockups If a parser process is terminated while holding a write lock, then it will lead to a deadlock (see https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Process.terminate). With SIGTERM, we don't want to terminate holding the lock. We also don't want a SIGINT to cause a partial write to the event stream. I tried using signal masks to avoid this but it doesn't work, see https://bugs.python.org/issue47139 Instead, add a signal handler and catch the calls around the critical section. We also need a thread lock to ensure other threads in the same process don't handle the signal until all the threads are not in the lock. (Bitbake rev: a40efaa5556a188dfe46c8d060adde37dc400dcd) Signed-off-by: Richard Purdie --- bitbake/lib/bb/cooker.py | 28 ++++++++++++++++++++++++++-- bitbake/lib/bb/server/process.py | 22 ++++++++++++++++++++-- 2 files changed, 46 insertions(+), 4 deletions(-) diff --git a/bitbake/lib/bb/cooker.py b/bitbake/lib/bb/cooker.py index d6fcd9e05c..7c0c5d4efa 100644 --- a/bitbake/lib/bb/cooker.py +++ b/bitbake/lib/bb/cooker.py @@ -2017,6 +2017,22 @@ class Parser(multiprocessing.Process): self.context = bb.utils.get_context().copy() self.handlers = bb.event.get_class_handlers().copy() self.profile = profile + self.queue_signals = False + self.signal_received = [] + self.signal_threadlock = threading.Lock() + + def catch_sig(self, signum, frame): + if self.queue_signals: + self.signal_received.append(signum) + else: + self.handle_sig(signum, frame) + + def handle_sig(self, signum, frame): + if signum == signal.SIGTERM: + signal.signal(signal.SIGTERM, signal.SIG_DFL) + os.kill(os.getpid(), signal.SIGTERM) + elif signum == signal.SIGINT: + signal.default_int_handler(signum, frame) def run(self): @@ -2036,9 +2052,17 @@ class Parser(multiprocessing.Process): prof.dump_stats(logfile) def realrun(self): - signal.signal(signal.SIGTERM, signal.SIG_DFL) + # Signal handling here is hard. We must not terminate any process or thread holding the write + # lock for the event stream as it will not be released, ever, and things will hang. + # Python handles signals in the main thread/process but they can be raised from any thread and + # we want to defer processing of any SIGTERM/SIGINT signal until we're outside the critical section + # and don't hold the lock (see server/process.py). We therefore always catch the signals (so any + # new thread should also do so) and we defer handling but we handle with the local thread lock + # held (a threading lock, not a multiprocessing one) so that no other thread in the process + # can be in the critical section. + signal.signal(signal.SIGTERM, self.catch_sig) signal.signal(signal.SIGHUP, signal.SIG_DFL) - signal.signal(signal.SIGINT, signal.SIG_IGN) + signal.signal(signal.SIGINT, self.catch_sig) bb.utils.set_process_name(multiprocessing.current_process().name) multiprocessing.util.Finalize(None, bb.codeparser.parser_cache_save, exitpriority=1) multiprocessing.util.Finalize(None, bb.fetch.fetcher_parse_save, exitpriority=1) diff --git a/bitbake/lib/bb/server/process.py b/bitbake/lib/bb/server/process.py index 7c587a9110..ce53fdc678 100644 --- a/bitbake/lib/bb/server/process.py +++ b/bitbake/lib/bb/server/process.py @@ -20,6 +20,7 @@ import os import sys import time import select +import signal import socket import subprocess import errno @@ -737,11 +738,28 @@ class ConnectionWriter(object): # Why bb.event needs this I have no idea self.event = self - def send(self, obj): - obj = multiprocessing.reduction.ForkingPickler.dumps(obj) + def _send(self, obj): with self.wlock: self.writer.send_bytes(obj) + def send(self, obj): + obj = multiprocessing.reduction.ForkingPickler.dumps(obj) + # See notes/code in CookerParser + # We must not terminate holding this lock else processes will hang. + # For SIGTERM, raising afterwards avoids this. + # For SIGINT, we don't want to have written partial data to the pipe. + # pthread_sigmask block/unblock would be nice but doesn't work, https://bugs.python.org/issue47139 + process = multiprocessing.current_process() + if process and hasattr(process, "queue_signals"): + with process.signal_threadlock: + process.queue_signals = True + self._send(obj) + process.queue_signals = False + for sig in process.signal_received.pop(): + process.handle_sig(sig, None) + else: + self._send(obj) + def fileno(self): return self.writer.fileno() -- cgit v1.2.3-54-g00ecf