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[3.9] bpo-40826: Fix GIL usage in PyOS_Readline() #20613

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Merged
merged 2 commits into from
Jun 3, 2020
Merged

[3.9] bpo-40826: Fix GIL usage in PyOS_Readline() #20613

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2686c49
bpo-40826: Fix GIL usage in PyOS_Readline() (GH-20579)
vstinner Jun 1, 2020
3c16f81
bpo-40826: Add _PyOS_InterruptOccurred(tstate) function (GH-20599)
vstinner Jun 3, 2020
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3 changes: 3 additions & 0 deletions Include/internal/pycore_pystate.h
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,9 @@ PyAPI_FUNC(int) _PyState_AddModule(
PyObject* module,
struct PyModuleDef* def);


PyAPI_FUNC(int) _PyOS_InterruptOccurred(PyThreadState *tstate);

#ifdef __cplusplus
}
#endif
Expand Down
22 changes: 16 additions & 6 deletions Lib/test/test_repl.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,9 @@ def spawn_repl(*args, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, **kw):
# test.support.script_helper.
env = kw.setdefault('env', dict(os.environ))
env['TERM'] = 'vt100'
return subprocess.Popen(cmd_line, executable=sys.executable,
return subprocess.Popen(cmd_line,
executable=sys.executable,
text=True,
stdin=subprocess.PIPE,
stdout=stdout, stderr=stderr,
**kw)
Expand All @@ -49,12 +51,11 @@ def test_no_memory(self):
sys.exit(0)
"""
user_input = dedent(user_input)
user_input = user_input.encode()
p = spawn_repl()
with SuppressCrashReport():
p.stdin.write(user_input)
output = kill_python(p)
self.assertIn(b'After the exception.', output)
self.assertIn('After the exception.', output)
# Exit code 120: Py_FinalizeEx() failed to flush stdout and stderr.
self.assertIn(p.returncode, (1, 120))

Expand Down Expand Up @@ -86,13 +87,22 @@ def test_multiline_string_parsing(self):
</test>"""
'''
user_input = dedent(user_input)
user_input = user_input.encode()
p = spawn_repl()
with SuppressCrashReport():
p.stdin.write(user_input)
p.stdin.write(user_input)
output = kill_python(p)
self.assertEqual(p.returncode, 0)

def test_close_stdin(self):
user_input = dedent('''
import os
print("before close")
os.close(0)
''')
process = spawn_repl()
output = process.communicate(user_input)[0]
self.assertEqual(process.returncode, 0)
self.assertIn('before close', output)


if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-06-01-20-31-07.bpo-40826.XCI4M2.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix GIL usage in :c:func:`PyOS_Readline`: lock the GIL to set an exception
and pass the Python thread state when checking if there is a pending signal.
18 changes: 15 additions & 3 deletions Modules/signalmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1779,11 +1779,13 @@ PyOS_FiniInterrupts(void)
finisignal();
}


// The caller doesn't have to hold the GIL
int
PyOS_InterruptOccurred(void)
_PyOS_InterruptOccurred(PyThreadState *tstate)
{
PyInterpreterState *interp = _PyInterpreterState_GET();
if (!_Py_ThreadCanHandleSignals(interp)) {
assert(tstate != NULL);
if (!_Py_ThreadCanHandleSignals(tstate->interp)) {
return 0;
}

Expand All @@ -1795,6 +1797,16 @@ PyOS_InterruptOccurred(void)
return 1;
}


// The caller must to hold the GIL
int
PyOS_InterruptOccurred(void)
{
PyThreadState *tstate = _PyThreadState_GET();
return _PyOS_InterruptOccurred(tstate);
}


static void
_clear_pending_signals(void)
{
Expand Down
118 changes: 85 additions & 33 deletions Parser/myreadline.c
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Expand Up @@ -24,25 +24,36 @@ static PyThread_type_lock _PyOS_ReadlineLock = NULL;
int (*PyOS_InputHook)(void) = NULL;

/* This function restarts a fgets() after an EINTR error occurred
except if PyOS_InterruptOccurred() returns true. */
except if _PyOS_InterruptOccurred() returns true. */

static int
my_fgets(char *buf, int len, FILE *fp)
my_fgets(PyThreadState* tstate, char *buf, int len, FILE *fp)
{
#ifdef MS_WINDOWS
HANDLE hInterruptEvent;
HANDLE handle;
_Py_BEGIN_SUPPRESS_IPH
handle = (HANDLE)_get_osfhandle(fileno(fp));
_Py_END_SUPPRESS_IPH

/* bpo-40826: fgets(fp) does crash if fileno(fp) is closed */
if (handle == INVALID_HANDLE_VALUE) {
return -1; /* EOF */
}
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_get_osfhandle sets errno to EBADF if the fd is closed, so this is an error case that should return -2. That's consistent with Linux fgets for this case.

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my_fgets() is not a generic wrapper for fgets(), but a helper function for PyOS_StdioReadline() which doesn't use errno.

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If you see a bug in my change, please comment https://bugs.python.org/issue40826.

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I just thought it would be better to be consistent with the function's API -- returning -2 for an error -- and to be consistent how the same case would behave in Linux. Also, to not include a misleading /* EOF */ comment for a case that has nothing to do with EOF.

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Well... the caller handles -1 and -2 the same way :-) This PR is a backport to 3.9. If you want to adjust the behavior, you can propose a PR on the master branch ;-)

#endif
char *p;
int err;

while (1) {
if (PyOS_InputHook != NULL)
if (PyOS_InputHook != NULL) {
(void)(PyOS_InputHook)();
}

errno = 0;
clearerr(fp);
p = fgets(buf, len, fp);
if (p != NULL)
char *p = fgets(buf, len, fp);
if (p != NULL) {
return 0; /* No error */
err = errno;
}
int err = errno;

#ifdef MS_WINDOWS
/* Ctrl-C anywhere on the line or Ctrl-Z if the only character
on a line will set ERROR_OPERATION_ABORTED. Under normal
Expand All @@ -58,7 +69,7 @@ my_fgets(char *buf, int len, FILE *fp)
through to check for EOF.
*/
if (GetLastError()==ERROR_OPERATION_ABORTED) {
hInterruptEvent = _PyOS_SigintEvent();
HANDLE hInterruptEvent = _PyOS_SigintEvent();
switch (WaitForSingleObjectEx(hInterruptEvent, 10, FALSE)) {
case WAIT_OBJECT_0:
ResetEvent(hInterruptEvent);
Expand All @@ -68,23 +79,27 @@ my_fgets(char *buf, int len, FILE *fp)
}
}
#endif /* MS_WINDOWS */

if (feof(fp)) {
clearerr(fp);
return -1; /* EOF */
}

#ifdef EINTR
if (err == EINTR) {
int s;
PyEval_RestoreThread(_PyOS_ReadlineTState);
s = PyErr_CheckSignals();
PyEval_RestoreThread(tstate);
int s = PyErr_CheckSignals();
PyEval_SaveThread();
if (s < 0)
return 1;
/* try again */

if (s < 0) {
return 1;
}
/* try again */
continue;
}
#endif
if (PyOS_InterruptOccurred()) {

if (_PyOS_InterruptOccurred(tstate)) {
return 1; /* Interrupt */
}
return -2; /* Error */
Expand All @@ -98,7 +113,7 @@ my_fgets(char *buf, int len, FILE *fp)
extern char _get_console_type(HANDLE handle);

char *
_PyOS_WindowsConsoleReadline(HANDLE hStdIn)
_PyOS_WindowsConsoleReadline(PyThreadState *tstate, HANDLE hStdIn)
{
static wchar_t wbuf_local[1024 * 16];
const DWORD chunk_size = 1024;
Expand Down Expand Up @@ -133,11 +148,12 @@ _PyOS_WindowsConsoleReadline(HANDLE hStdIn)
if (WaitForSingleObjectEx(hInterruptEvent, 100, FALSE)
== WAIT_OBJECT_0) {
ResetEvent(hInterruptEvent);
PyEval_RestoreThread(_PyOS_ReadlineTState);
PyEval_RestoreThread(tstate);
s = PyErr_CheckSignals();
PyEval_SaveThread();
if (s < 0)
if (s < 0) {
goto exit;
}
}
break;
}
Expand All @@ -150,17 +166,22 @@ _PyOS_WindowsConsoleReadline(HANDLE hStdIn)
if (wbuf == wbuf_local) {
wbuf[total_read] = '\0';
wbuf = (wchar_t*)PyMem_RawMalloc(wbuflen * sizeof(wchar_t));
if (wbuf)
if (wbuf) {
wcscpy_s(wbuf, wbuflen, wbuf_local);
}
else {
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
goto exit;
}
}
else {
wchar_t *tmp = PyMem_RawRealloc(wbuf, wbuflen * sizeof(wchar_t));
if (tmp == NULL) {
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
goto exit;
}
wbuf = tmp;
Expand All @@ -169,33 +190,45 @@ _PyOS_WindowsConsoleReadline(HANDLE hStdIn)

if (wbuf[0] == '\x1a') {
buf = PyMem_RawMalloc(1);
if (buf)
if (buf) {
buf[0] = '\0';
}
else {
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
}
goto exit;
}

u8len = WideCharToMultiByte(CP_UTF8, 0, wbuf, total_read, NULL, 0, NULL, NULL);
u8len = WideCharToMultiByte(CP_UTF8, 0,
wbuf, total_read,
NULL, 0,
NULL, NULL);
buf = PyMem_RawMalloc(u8len + 1);
if (buf == NULL) {
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
goto exit;
}
u8len = WideCharToMultiByte(CP_UTF8, 0, wbuf, total_read, buf, u8len, NULL, NULL);

u8len = WideCharToMultiByte(CP_UTF8, 0,
wbuf, total_read,
buf, u8len,
NULL, NULL);
buf[u8len] = '\0';

exit:
if (wbuf != wbuf_local)
if (wbuf != wbuf_local) {
PyMem_RawFree(wbuf);
}

if (err) {
PyEval_RestoreThread(_PyOS_ReadlineTState);
PyEval_RestoreThread(tstate);
PyErr_SetFromWindowsErr(err);
PyEval_SaveThread();
}

return buf;
}

Expand All @@ -209,6 +242,8 @@ PyOS_StdioReadline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
{
size_t n;
char *p, *pr;
PyThreadState *tstate = _PyOS_ReadlineTState;
assert(tstate != NULL);

#ifdef MS_WINDOWS
if (!Py_LegacyWindowsStdioFlag && sys_stdin == stdin) {
Expand All @@ -230,7 +265,9 @@ PyOS_StdioReadline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
if (wlen) {
wbuf = PyMem_RawMalloc(wlen * sizeof(wchar_t));
if (wbuf == NULL) {
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
return NULL;
}
wlen = MultiByteToWideChar(CP_UTF8, 0, prompt, -1,
Expand All @@ -249,24 +286,27 @@ PyOS_StdioReadline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
}
}
clearerr(sys_stdin);
return _PyOS_WindowsConsoleReadline(hStdIn);
return _PyOS_WindowsConsoleReadline(tstate, hStdIn);
}
}
#endif

n = 100;
p = (char *)PyMem_RawMalloc(n);
if (p == NULL) {
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
return NULL;
}

fflush(sys_stdout);
if (prompt)
if (prompt) {
fprintf(stderr, "%s", prompt);
}
fflush(stderr);

switch (my_fgets(p, (int)n, sys_stdin)) {
switch (my_fgets(tstate, p, (int)n, sys_stdin)) {
case 0: /* Normal case */
break;
case 1: /* Interrupt */
Expand All @@ -278,29 +318,40 @@ PyOS_StdioReadline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
*p = '\0';
break;
}

n = strlen(p);
while (n > 0 && p[n-1] != '\n') {
size_t incr = n+2;
if (incr > INT_MAX) {
PyMem_RawFree(p);
PyEval_RestoreThread(tstate);
PyErr_SetString(PyExc_OverflowError, "input line too long");
PyEval_SaveThread();
return NULL;
}

pr = (char *)PyMem_RawRealloc(p, n + incr);
if (pr == NULL) {
PyMem_RawFree(p);
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
return NULL;
}
p = pr;
if (my_fgets(p+n, (int)incr, sys_stdin) != 0)

if (my_fgets(tstate, p+n, (int)incr, sys_stdin) != 0) {
break;
}
n += strlen(p+n);
}

pr = (char *)PyMem_RawRealloc(p, n+1);
if (pr == NULL) {
PyMem_RawFree(p);
PyEval_RestoreThread(tstate);
PyErr_NoMemory();
PyEval_SaveThread();
return NULL;
}
return pr;
Expand All @@ -323,7 +374,8 @@ PyOS_Readline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
char *rv, *res;
size_t len;

if (_PyOS_ReadlineTState == _PyThreadState_GET()) {
PyThreadState *tstate = _PyThreadState_GET();
if (_PyOS_ReadlineTState == tstate) {
PyErr_SetString(PyExc_RuntimeError,
"can't re-enter readline");
return NULL;
Expand All @@ -342,7 +394,7 @@ PyOS_Readline(FILE *sys_stdin, FILE *sys_stdout, const char *prompt)
}
}

_PyOS_ReadlineTState = _PyThreadState_GET();
_PyOS_ReadlineTState = tstate;
Py_BEGIN_ALLOW_THREADS
PyThread_acquire_lock(_PyOS_ReadlineLock, 1);

Expand Down