[New-bugs-announce] [issue14173] PyOS_FiniInterupts leaves signal.getsignal segfaulty

[Ferringb]

New submission from Ferringb <ferringb at gmail.com>:

During Py_Finalize (pythonrun.c), it does the following:
1) suppress signal handling PyOs_FiniInterupts
2) clear caches
3) force gc collection; first for objects, then via wiping modules.

The problem is that for unix OSs, Modules/signal.c's PyOs_FiniInterrupts leaves itself in a state where its internal Handlers are effectively reset to NULL, except the various functions don't properly handle that scenario.

Attached is a test case demonstrating it; it segfaults on every python version I've tested (2.4->3.2; haven't tried 3.3).

Since this *only* occurs during the final gc sweep when modules are destroyed, its a bit of a pain in the ass to detect that we're in that scenario, and that we must not touch signal.getsignal lest it segfault the interp.  That said,

def _SignalModuleUsable():
try:
  signal.signal(signal.SIGUSR1, signal.signal(signal.SIGUSR1, some_handler))
  return True
except (TypeError, AttributeError, SystemError):
  # we were invoked in a module cleanup context.
  return False

does manage to poke the api just right so that it can be detected w/out segfaulting the interp.

Finally, note that while folks could point at __del__... its not really at fault.  Doing a proper weakref.ref finalizer can trigger the same- the fault is signal.c's PyOs_FiniInterrupts leaving the signal module in a bad state.  For the testcase, I used __del__ just because it was quicker/less code to do so.

----------
components: Interpreter Core
files: test.py
messages: 154758
nosy: ferringb
priority: normal
severity: normal
status: open
title: PyOS_FiniInterupts leaves signal.getsignal segfaulty
type: crash
versions: Python 2.6, Python 2.7, Python 3.1, Python 3.2
Added file: http://bugs.python.org/file24703/test.py

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