https://github.com/python/cpython/commit/6b37486184590d19c6f24e620545ec8f8f65e4c7
commit: 6b37486184590d19c6f24e620545ec8f8f65e4c7
branch: 3.11
author: Diego Russo <diego.ru...@arm.com>
committer: pablogsal <pablog...@gmail.com>
date: 2025-03-11T15:31:03Z
summary:
[3.11] gh-106883 Fix deadlock in threaded application (#117332)
When using threaded applications, there is a high risk of a deadlock in
the interpreter. It's a lock ordering deadlock with HEAD_LOCK(&_PyRuntime); and
the GIL.
By disabling the GC during the _PyThread_CurrentFrames() and
_PyThread_CurrentExceptions() calls fixes the issue.
files:
A Misc/NEWS.d/next/C API/2024-04-05-14-32-21.gh-issue-106883.OKmc0Q.rst
M Lib/test/test_sys.py
M Python/pystate.c
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 86cf1a794f973c..28931039f3792e 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -14,6 +14,7 @@
from test.support.script_helper import assert_python_ok, assert_python_failure
from test.support import threading_helper
from test.support import import_helper
+from test.support import skip_if_sanitizer
import textwrap
import unittest
import warnings
@@ -471,6 +472,79 @@ def g456():
leave_g.set()
t.join()
+ @skip_if_sanitizer(memory=True, address=True, reason= "Test too slow "
+ "when the address sanitizer is enabled.")
+ @threading_helper.reap_threads
+ @threading_helper.requires_working_threading()
+ @support.requires_fork()
+ def test_current_frames_exceptions_deadlock(self):
+ """
+ Reproduce the bug raised in GH-106883 and GH-116969.
+ """
+ import threading
+ import time
+ import signal
+
+ class MockObject:
+ def __init__(self):
+ # Create some garbage
+ self._list = list(range(10000))
+ # Call the functions under test
+ self._trace = sys._current_frames()
+ self._exceptions = sys._current_exceptions()
+
+ def __del__(self):
+ # The presence of the __del__ method causes the deadlock when
+ # there is one thread executing the _current_frames or
+ # _current_exceptions functions and the other thread is
+ # running the GC:
+ # thread 1 has the interpreter lock and it is trying to
+ # acquire the GIL; thread 2 holds the GIL but is trying to
+ # acquire the interpreter lock.
+ # When the GC is running and it finds that an
+ # object has the __del__ method, it needs to execute the
+ # Python code in it and it requires the GIL to execute it
+ # (which will never happen because it is held by another thread
+ # blocked on the acquisition of the interpreter lock)
+ pass
+
+ def thread_function(num_objects):
+ obj = None
+ for _ in range(num_objects):
+ obj = MockObject()
+
+ # The number of objects should be big enough to increase the
+ # chances to call the GC.
+ NUM_OBJECTS = 1000
+ NUM_THREADS = 10
+
+ # 40 seconds should be enough for the test to be executed: if it
+ # is more than 40 seconds it means that the process is in deadlock
+ # hence the test fails
+ TIMEOUT = 40
+
+ # Test the sys._current_frames and sys._current_exceptions calls
+ pid = os.fork()
+ if pid: # parent process
+ try:
+ support.wait_process(pid, exitcode=0, timeout=TIMEOUT)
+ except KeyboardInterrupt:
+ # When pressing CTRL-C kill the deadlocked process
+ os.kill(pid, signal.SIGTERM)
+ raise
+ else: # child process
+ # Run the actual test in the forked process.
+ threads = []
+ for i in range(NUM_THREADS):
+ thread = threading.Thread(
+ target=thread_function, args=(NUM_OBJECTS,)
+ )
+ threads.append(thread)
+ thread.start()
+ for t in threads:
+ t.join()
+ os._exit(0)
+
@threading_helper.reap_threads
@threading_helper.requires_working_threading()
def test_current_exceptions(self):
diff --git a/Misc/NEWS.d/next/C
API/2024-04-05-14-32-21.gh-issue-106883.OKmc0Q.rst b/Misc/NEWS.d/next/C
API/2024-04-05-14-32-21.gh-issue-106883.OKmc0Q.rst
new file mode 100644
index 00000000000000..01c7fb0c790708
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2024-04-05-14-32-21.gh-issue-106883.OKmc0Q.rst
@@ -0,0 +1 @@
+Disable GC during the _PyThread_CurrentFrames() and
_PyThread_CurrentExceptions() calls to avoid the interpreter to deadlock.
diff --git a/Python/pystate.c b/Python/pystate.c
index db2ce878af64ec..a45116665fe195 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1398,6 +1398,9 @@ _PyThread_CurrentFrames(void)
return NULL;
}
+ // gh-106883: Disable the GC as this can cause the interpreter to deadlock
+ int gc_was_enabled = PyGC_Disable();
+
/* for i in all interpreters:
* for t in all of i's thread states:
* if t's frame isn't NULL, map t's id to its frame
@@ -1440,6 +1443,12 @@ _PyThread_CurrentFrames(void)
done:
HEAD_UNLOCK(runtime);
+
+ // Once the runtime is released, the GC can be reenabled.
+ if (gc_was_enabled) {
+ PyGC_Enable();
+ }
+
return result;
}
@@ -1459,6 +1468,9 @@ _PyThread_CurrentExceptions(void)
return NULL;
}
+ // gh-106883: Disable the GC as this can cause the interpreter to deadlock
+ int gc_was_enabled = PyGC_Disable();
+
/* for i in all interpreters:
* for t in all of i's thread states:
* if t's frame isn't NULL, map t's id to its frame
@@ -1499,6 +1511,12 @@ _PyThread_CurrentExceptions(void)
done:
HEAD_UNLOCK(runtime);
+
+ // Once the runtime is released, the GC can be reenabled.
+ if (gc_was_enabled) {
+ PyGC_Enable();
+ }
+
return result;
}
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