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Possible race condition between signal catching and signal.signal #87572

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pitrou opened this issue Mar 4, 2021 · 10 comments
Closed

Possible race condition between signal catching and signal.signal #87572

pitrou opened this issue Mar 4, 2021 · 10 comments
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3.8 only security fixes 3.9 only security fixes 3.10 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@pitrou
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pitrou commented Mar 4, 2021

BPO 43406
Nosy @pitrou, @vstinner, @miss-islington
PRs
  • bpo-43406: Fix possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler #24756
  • [3.9] bpo-43406: Fix possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler (GH-24756) #24761
  • [3.8] bpo-43406: Fix possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler (GH-24756) #24762
  • bpo-43356: Allow passing a signal number to interrupt_main() #24755
  • bpo-43406: Fix test_signal.test_stress_modifying_handlers() #24815
  • [3.8] bpo-43406: Fix test_signal.test_stress_modifying_handlers() (GH-24815) #24816
  • [3.9] bpo-43406: Fix test_signal.test_stress_modifying_handlers() (GH-24815) #24817
  • Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
    closed_at = <Date 2021-03-10.14:30:05.963>
    created_at = <Date 2021-03-04.21:31:08.922>
    labels = ['interpreter-core', 'type-bug', '3.8', '3.9', '3.10', 'library']
    title = 'Possible race condition between signal catching and signal.signal'
    updated_at = <Date 2021-03-10.15:11:06.044>
    user = 'https://github.com/pitrou'

    bugs.python.org fields:

    activity = <Date 2021-03-10.15:11:06.044>
    actor = 'vstinner'
    assignee = 'none'
    closed = True
    closed_date = <Date 2021-03-10.14:30:05.963>
    closer = 'vstinner'
    components = ['Interpreter Core', 'Library (Lib)']
    creation = <Date 2021-03-04.21:31:08.922>
    creator = 'pitrou'
    dependencies = []
    files = []
    hgrepos = []
    issue_num = 43406
    keywords = ['patch']
    message_count = 10.0
    messages = ['388131', '388132', '388150', '388202', '388203', '388429', '388431', '388435', '388437', '388438']
    nosy_count = 4.0
    nosy_names = ['pitrou', 'vstinner', 'neologix', 'miss-islington']
    pr_nums = ['24756', '24761', '24762', '24755', '24815', '24816', '24817']
    priority = 'normal'
    resolution = 'fixed'
    stage = 'resolved'
    status = 'closed'
    superseder = None
    type = 'behavior'
    url = 'https://bugs.python.org/issue43406'
    versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

    @pitrou
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    pitrou commented Mar 4, 2021

    We can receive signals (at the C level, in trip_signal() in signalmodule.c) while signal.signal is being called to modify the corresponding handler. Later when PyErr_CheckSignals() is called to handle the given signal, the handler may be a non-callable object and will raise a cryptic asynchronous exception.

    @pitrou pitrou added 3.8 only security fixes 3.9 only security fixes 3.10 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Mar 4, 2021
    @pitrou
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    pitrou commented Mar 4, 2021

    Here is a reproducer:
    https://gist.github.com/pitrou/e5a566e644730516b51de71145c5ea06

    If you execute it, it will fail after a few iterations:

    sig 2
    sig 2
    sig 2
    Traceback (most recent call last):
      File "/home/antoine/cpython/default/setinterrupt.py", line 30, in <module>
        main()
      File "/home/antoine/cpython/default/setinterrupt.py", line 27, in main
        cycle_handlers(signum)
      File "/home/antoine/cpython/default/setinterrupt.py", line 19, in cycle_handlers
        signal.signal(signum, handler)
      File "/home/antoine/cpython/default/Lib/signal.py", line 48, in signal
        return _int_to_enum(handler, Handlers)
      File "/home/antoine/cpython/default/Lib/signal.py", line 30, in _int_to_enum
        return enum_klass(value)
      File "/home/antoine/cpython/default/Lib/enum.py", line 606, in __call__
        return cls.__new__(cls, value)
      File "/home/antoine/cpython/default/Lib/enum.py", line 927, in __new__
        ve_exc = ValueError("%r is not a valid %s" % (value, cls.__qualname__))
    TypeError: 'int' object is not callable

    @pitrou
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    pitrou commented Mar 5, 2021

    New changeset 68245b7 by Antoine Pitrou in branch 'master':
    bpo-43406: Fix possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler (GH-24756)
    68245b7

    @miss-islington
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    New changeset 1385f83 by Miss Islington (bot) in branch '3.9':
    [3.9] bpo-43406: Fix possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler (GH-24756) (GH-24761)
    1385f83

    @miss-islington
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    New changeset 4715be8 by Antoine Pitrou in branch '3.8':
    [3.8] bpo-43406: Fix possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler (GH-24756) (GH-24762)
    4715be8

    @pitrou pitrou closed this as completed Mar 6, 2021
    @pitrou pitrou closed this as completed Mar 6, 2021
    @vstinner
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    The change added a new functional test. As I expected, it failed on "AMD64 Debian root". I expected it because the previously added functional test failed failed on "AMD64 Debian root", I reported the race condition in 2017 and it's still not fixed: bpo-30849.

    The new functional test has two race conditions.

    I reopen the issue.

    == Race condition 1 ==

    AMD64 Debian root 3.x:
    https://buildbot.python.org/all/#/builders/345/builds/903

    0:15:05 load avg: 2.58 [137/427/1] test_signal failed (env changed) (1 min 13 sec)
    Warning -- Unraisable exception
    Traceback (most recent call last):
      File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/threading.py", line 1067, in _wait_for_tstate_lock
        elif lock.acquire(block, timeout):
    OSError: Signal 10 ignored due to race condition

    == Race condition 2 ==

    By the way, the test also fails when I stress my laptop:

    $ ./python -m test --fail-env-changed test_signal -F -j40 -m test_stress_modifying_handlers -v
    == CPython 3.10.0a6+ (heads/master:a9c03d7fb7, Mar 10 2021, 12:41:26) [GCC 10.2.1 20201125 (Red Hat 10.2.1-9)]
    == Linux-5.10.15-200.fc33.x86_64-x86_64-with-glibc2.32 little-endian
    == cwd: /home/vstinner/python/master/build/test_python_223315æ
    == CPU count: 8
    == encodings: locale=UTF-8, FS=utf-8
    0:00:00 load avg: 4.17 Run tests in parallel using 40 child processes
    (...)
    0:00:05 load avg: 7.52 [  5/1] test_signal failed
    test_stress_modifying_handlers (test.test_signal.StressTest) ... FAIL

    ======================================================================
    FAIL: test_stress_modifying_handlers (test.test_signal.StressTest)
    ----------------------------------------------------------------------

    Traceback (most recent call last):
      File "/home/vstinner/python/master/Lib/test/test_signal.py", line 1297, in test_stress_modifying_handlers
        self.assertGreater(num_received_signals, 0)
    AssertionError: 0 not greater than 0

    Ran 1 test in 0.039s

    FAILED (failures=1)
    test test_signal failed
    (...)

    @vstinner vstinner reopened this Mar 10, 2021
    @vstinner vstinner reopened this Mar 10, 2021
    @vstinner
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    The new functional test has two race conditions.

    I don't think that it's a bug in Python, but more race conditions in the test.

    @vstinner
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    New changeset 1fa17e8 by Victor Stinner in branch 'master':
    bpo-43406: Fix test_signal.test_stress_modifying_handlers() (GH-24815)
    1fa17e8

    @miss-islington
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    New changeset ac5e23c by Miss Islington (bot) in branch '3.8':
    bpo-43406: Fix test_signal.test_stress_modifying_handlers() (GH-24815)
    ac5e23c

    @vstinner
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    New changeset 531f2eb by Miss Islington (bot) in branch '3.9':
    bpo-43406: Fix test_signal.test_stress_modifying_handlers() (GH-24815) (GH-24817)
    531f2eb

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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    Labels
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