https://github.com/python/cpython/commit/befcfdfdaba15ecae38739ecabebd8046c1b1977
commit: befcfdfdaba15ecae38739ecabebd8046c1b1977
branch: main
author: Peter Bierma <[email protected]>
committer: colesbury <[email protected]>
date: 2025-01-03T14:14:57-05:00
summary:
gh-128400: Only show the current thread in `faulthandler` if the GIL is
disabled (GH-128425)
files:
A Misc/NEWS.d/next/Library/2025-01-02-15-20-17.gh-issue-128400.UMiG4f.rst
M Doc/library/faulthandler.rst
M Lib/test/test_faulthandler.py
M Modules/faulthandler.c
diff --git a/Doc/library/faulthandler.rst b/Doc/library/faulthandler.rst
index 4067d7912b88b2..b81da4af3cff58 100644
--- a/Doc/library/faulthandler.rst
+++ b/Doc/library/faulthandler.rst
@@ -91,6 +91,10 @@ Fault handler state
The dump now mentions if a garbage collector collection is running
if *all_threads* is true.
+ .. versionchanged:: next
+ Only the current thread is dumped if the :term:`GIL` is disabled to
+ prevent the risk of data races.
+
.. function:: disable()
Disable the fault handler: uninstall the signal handlers installed by
diff --git a/Lib/test/test_faulthandler.py b/Lib/test/test_faulthandler.py
index fd56dee5d842ac..2088793cbb9387 100644
--- a/Lib/test/test_faulthandler.py
+++ b/Lib/test/test_faulthandler.py
@@ -100,7 +100,12 @@ def check_error(self, code, lineno, fatal_error, *,
Raise an error if the output doesn't match the expected format.
"""
- if all_threads:
+ all_threads_disabled = (
+ (not py_fatal_error)
+ and all_threads
+ and (not sys._is_gil_enabled())
+ )
+ if all_threads and not all_threads_disabled:
if know_current_thread:
header = 'Current thread 0x[0-9a-f]+'
else:
@@ -111,8 +116,10 @@ def check_error(self, code, lineno, fatal_error, *,
if py_fatal_error:
regex.append("Python runtime state: initialized")
regex.append('')
+ if all_threads_disabled:
+ regex.append("<Cannot show all threads while the GIL is disabled>")
regex.append(fr'{header} \(most recent call first\):')
- if garbage_collecting:
+ if garbage_collecting and not all_threads_disabled:
regex.append(' Garbage-collecting')
regex.append(fr' File "<string>", line {lineno} in {function}')
regex = '\n'.join(regex)
diff --git
a/Misc/NEWS.d/next/Library/2025-01-02-15-20-17.gh-issue-128400.UMiG4f.rst
b/Misc/NEWS.d/next/Library/2025-01-02-15-20-17.gh-issue-128400.UMiG4f.rst
new file mode 100644
index 00000000000000..f9d5f84224c8dc
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-01-02-15-20-17.gh-issue-128400.UMiG4f.rst
@@ -0,0 +1,2 @@
+Only show the current thread in :mod:`faulthandler` on the :term:`free
+threaded <free threading>` build to prevent races.
diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index 2d16028a5232d0..b44b964b29484b 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -1,4 +1,5 @@
#include "Python.h"
+#include "pycore_ceval.h" // _PyEval_IsGILEnabled
#include "pycore_initconfig.h" // _PyStatus_ERR
#include "pycore_pyerrors.h" // _Py_DumpExtensionModules
#include "pycore_pystate.h" // _PyThreadState_GET()
@@ -27,6 +28,8 @@
# include <sys/auxv.h> // getauxval()
#endif
+/* Sentinel to ignore all_threads on free-threading */
+#define FT_IGNORE_ALL_THREADS 2
/* Allocate at maximum 100 MiB of the stack to raise the stack overflow */
#define STACK_OVERFLOW_MAX_SIZE (100 * 1024 * 1024)
@@ -201,10 +204,13 @@ faulthandler_dump_traceback(int fd, int all_threads,
PyGILState_GetThisThreadState(). */
PyThreadState *tstate = PyGILState_GetThisThreadState();
- if (all_threads) {
+ if (all_threads == 1) {
(void)_Py_DumpTracebackThreads(fd, NULL, tstate);
}
else {
+ if (all_threads == FT_IGNORE_ALL_THREADS) {
+ PUTS(fd, "<Cannot show all threads while the GIL is disabled>\n");
+ }
if (tstate != NULL)
_Py_DumpTraceback(fd, tstate);
}
@@ -271,6 +277,27 @@ faulthandler_disable_fatal_handler(fault_handler_t
*handler)
#endif
}
+static int
+deduce_all_threads(void)
+{
+#ifndef Py_GIL_DISABLED
+ return fatal_error.all_threads;
+#else
+ if (fatal_error.all_threads == 0) {
+ return 0;
+ }
+ // We can't use _PyThreadState_GET, so use the stored GILstate one
+ PyThreadState *tstate = PyGILState_GetThisThreadState();
+ if (tstate == NULL) {
+ return 0;
+ }
+
+ /* In theory, it's safe to dump all threads if the GIL is enabled */
+ return _PyEval_IsGILEnabled(tstate)
+ ? fatal_error.all_threads
+ : FT_IGNORE_ALL_THREADS;
+#endif
+}
/* Handler for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals.
@@ -325,7 +352,7 @@ faulthandler_fatal_error(int signum)
PUTS(fd, "\n\n");
}
- faulthandler_dump_traceback(fd, fatal_error.all_threads,
+ faulthandler_dump_traceback(fd, deduce_all_threads(),
fatal_error.interp);
_Py_DumpExtensionModules(fd, fatal_error.interp);
@@ -401,7 +428,7 @@ faulthandler_exc_handler(struct _EXCEPTION_POINTERS
*exc_info)
}
}
- faulthandler_dump_traceback(fd, fatal_error.all_threads,
+ faulthandler_dump_traceback(fd, deduce_all_threads(),
fatal_error.interp);
/* call the next exception handler */
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