diff --git a/Misc/NEWS.d/next/Library/2019-08-21-13-43-04.bpo-37851.mIIfD_.rst b/Misc/NEWS.d/next/Library/2019-08-21-13-43-04.bpo-37851.mIIfD_.rst new file mode 100644 index 000000000000000..997011f023f2729 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2019-08-21-13-43-04.bpo-37851.mIIfD_.rst @@ -0,0 +1,3 @@ +The :mod:`faulthandler` module no longer allocates its alternative stack at +Python startup. Now the stack is only allocated at the first faulthandler +usage. diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c index 5dbbcad057e643e..35e7b34c29ccd5d 100644 --- a/Modules/faulthandler.c +++ b/Modules/faulthandler.c @@ -125,7 +125,13 @@ static fault_handler_t faulthandler_handlers[] = { static const size_t faulthandler_nsignals = \ Py_ARRAY_LENGTH(faulthandler_handlers); -#ifdef HAVE_SIGALTSTACK +/* Using an alternative stack requires sigaltstack() + and sigaction() SA_ONSTACK */ +#if defined(HAVE_SIGALTSTACK) && defined(HAVE_SIGACTION) +# define FAULTHANDLER_USE_ALT_STACK +#endif + +#ifdef FAULTHANDLER_USE_ALT_STACK static stack_t stack; static stack_t old_stack; #endif @@ -427,6 +433,36 @@ faulthandler_exc_handler(struct _EXCEPTION_POINTERS *exc_info) } #endif + +#ifdef FAULTHANDLER_USE_ALT_STACK +static int +faulthandler_allocate_stack(void) +{ + if (stack.ss_sp != NULL) { + return 0; + } + /* Allocate an alternate stack for faulthandler() signal handler + to be able to execute a signal handler on a stack overflow error */ + stack.ss_sp = PyMem_Malloc(stack.ss_size); + if (stack.ss_sp == NULL) { + PyErr_NoMemory(); + return -1; + } + + int err = sigaltstack(&stack, &old_stack); + if (err) { + /* Release the stack to retry sigaltstack() next time */ + PyMem_Free(stack.ss_sp); + stack.ss_sp = NULL; + + PyErr_SetFromErrno(PyExc_OSError); + return -1; + } + return 0; +} +#endif + + /* Install the handler for fatal signals, faulthandler_fatal_error(). */ static int @@ -437,32 +473,35 @@ faulthandler_enable(void) } fatal_error.enabled = 1; +#ifdef FAULTHANDLER_USE_ALT_STACK + if (faulthandler_allocate_stack() < 0) { + return -1; + } +#endif + for (size_t i=0; i < faulthandler_nsignals; i++) { fault_handler_t *handler; -#ifdef HAVE_SIGACTION - struct sigaction action; -#endif int err; handler = &faulthandler_handlers[i]; assert(!handler->enabled); #ifdef HAVE_SIGACTION + struct sigaction action; action.sa_handler = faulthandler_fatal_error; sigemptyset(&action.sa_mask); /* Do not prevent the signal from being received from within its own signal handler */ action.sa_flags = SA_NODEFER; -#ifdef HAVE_SIGALTSTACK - if (stack.ss_sp != NULL) { - /* Call the signal handler on an alternate signal stack - provided by sigaltstack() */ - action.sa_flags |= SA_ONSTACK; - } +#ifdef FAULTHANDLER_USE_ALT_STACK + assert(stack.ss_sp != NULL); + /* Call the signal handler on an alternate signal stack + provided by sigaltstack() */ + action.sa_flags |= SA_ONSTACK; #endif err = sigaction(handler->signum, &action, &handler->previous); #else handler->previous = signal(handler->signum, - faulthandler_fatal_error); + faulthandler_fatal_error); err = (handler->previous == SIG_ERR); #endif if (err) { @@ -676,17 +715,37 @@ faulthandler_dump_traceback_later(PyObject *self, } tstate = get_thread_state(); - if (tstate == NULL) + if (tstate == NULL) { return NULL; + } fd = faulthandler_get_fileno(&file); - if (fd < 0) + if (fd < 0) { return NULL; + } + + if (!thread.running) { + thread.running = PyThread_allocate_lock(); + if (!thread.running) { + return PyErr_NoMemory(); + } + } + if (!thread.cancel_event) { + thread.cancel_event = PyThread_allocate_lock(); + if (!thread.cancel_event || !thread.running) { + return PyErr_NoMemory(); + } + + /* cancel_event starts to be acquired: it's only released to cancel + the thread. */ + PyThread_acquire_lock(thread.cancel_event, 1); + } /* format the timeout */ header = format_timeout(timeout_us); - if (header == NULL) + if (header == NULL) { return PyErr_NoMemory(); + } header_len = strlen(header); /* Cancel previous thread, if running */ @@ -728,9 +787,10 @@ faulthandler_cancel_dump_traceback_later_py(PyObject *self, } #endif /* FAULTHANDLER_LATER */ + #ifdef FAULTHANDLER_USER static int -faulthandler_register(int signum, int chain, _Py_sighandler_t *p_previous) +faulthandler_register(int signum, int chain, _Py_sighandler_t *previous_p) { #ifdef HAVE_SIGACTION struct sigaction action; @@ -745,19 +805,19 @@ faulthandler_register(int signum, int chain, _Py_sighandler_t *p_previous) own signal handler */ action.sa_flags = SA_NODEFER; } -#ifdef HAVE_SIGALTSTACK - if (stack.ss_sp != NULL) { - /* Call the signal handler on an alternate signal stack - provided by sigaltstack() */ - action.sa_flags |= SA_ONSTACK; - } +#ifdef FAULTHANDLER_USE_ALT_STACK + assert(stack.ss_sp != NULL); + /* Call the signal handler on an alternate signal stack + provided by sigaltstack() */ + action.sa_flags |= SA_ONSTACK; #endif - return sigaction(signum, &action, p_previous); + return sigaction(signum, &action, previous_p); #else _Py_sighandler_t previous; previous = signal(signum, faulthandler_user); - if (p_previous != NULL) - *p_previous = previous; + if (previous_p != NULL) { + *previous_p = previous; + } return (previous == SIG_ERR); #endif } @@ -861,6 +921,12 @@ faulthandler_register_py(PyObject *self, user = &user_signals[signum]; if (!user->enabled) { +#ifdef FAULTHANDLER_USE_ALT_STACK + if (faulthandler_allocate_stack() < 0) { + return NULL; + } +#endif + err = faulthandler_register(signum, chain, &previous); if (err) { PyErr_SetFromErrno(PyExc_OSError); @@ -1094,7 +1160,7 @@ faulthandler_fatal_error_py(PyObject *self, PyObject *args) Py_RETURN_NONE; } -#if defined(HAVE_SIGALTSTACK) && defined(HAVE_SIGACTION) +#if defined(FAULTHANDLER_USE_ALT_STACK) #define FAULTHANDLER_STACK_OVERFLOW #ifdef __INTEL_COMPILER @@ -1153,7 +1219,7 @@ faulthandler_stack_overflow(PyObject *self, PyObject *Py_UNUSED(ignored)) size, depth); return NULL; } -#endif /* defined(HAVE_SIGALTSTACK) && defined(HAVE_SIGACTION) */ +#endif /* defined(FAULTHANDLER_USE_ALT_STACK) && defined(HAVE_SIGACTION) */ static int @@ -1318,35 +1384,18 @@ faulthandler_init_enable(void) PyStatus _PyFaulthandler_Init(int enable) { -#ifdef HAVE_SIGALTSTACK - int err; - - /* Try to allocate an alternate stack for faulthandler() signal handler to - * be able to allocate memory on the stack, even on a stack overflow. If it - * fails, ignore the error. */ +#ifdef FAULTHANDLER_USE_ALT_STACK + memset(&stack, 0, sizeof(stack)); stack.ss_flags = 0; /* bpo-21131: allocate dedicated stack of SIGSTKSZ*2 bytes, instead of just SIGSTKSZ bytes. Calling the previous signal handler in faulthandler signal handler uses more than SIGSTKSZ bytes of stack memory on some platforms. */ stack.ss_size = SIGSTKSZ * 2; - stack.ss_sp = PyMem_Malloc(stack.ss_size); - if (stack.ss_sp != NULL) { - err = sigaltstack(&stack, &old_stack); - if (err) { - PyMem_Free(stack.ss_sp); - stack.ss_sp = NULL; - } - } #endif + #ifdef FAULTHANDLER_LATER - thread.file = NULL; - thread.cancel_event = PyThread_allocate_lock(); - thread.running = PyThread_allocate_lock(); - if (!thread.cancel_event || !thread.running) { - return _PyStatus_ERR("failed to allocate locks for faulthandler"); - } - PyThread_acquire_lock(thread.cancel_event, 1); + memset(&thread, 0, sizeof(thread)); #endif if (enable) { @@ -1386,7 +1435,8 @@ void _PyFaulthandler_Fini(void) /* fatal */ faulthandler_disable(); -#ifdef HAVE_SIGALTSTACK + +#ifdef FAULTHANDLER_USE_ALT_STACK if (stack.ss_sp != NULL) { /* Fetch the current alt stack */ stack_t current_stack;