/* Test case for async-signal-safe _Fork (with respect to malloc).
Copyright (C) 2021-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, see <https://www.gnu.org/licenses/>. */
/* This test is similar to tst-mallocfork2.c, but specifically stress
the async-signal-safeness of _Fork on multithread environment. */
#include <array_length.h>
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <support/check.h>
#include <support/support.h>
#include <support/xsignal.h>
#include <support/xthread.h>
#include <support/xunistd.h>
#include <sys/wait.h>
/* How many malloc objects to keep arond. */
enum { malloc_objects = 1009 };
/* The maximum size of an object. */
enum { malloc_maximum_size = 70000 };
/* How many iterations the test performs before exiting. */
enum { iterations = 10000 };
/* Barrier for synchronization with the threads sending SIGUSR1
signals, to make it more likely that the signals arrive during a
fork/free/malloc call. */
static pthread_barrier_t barrier;
/* Set to 1 if SIGUSR1 is received. Used to detect a signal during
fork/free/malloc. */
static volatile sig_atomic_t sigusr1_received;
/* Periodically set to 1, to indicate that the thread is making
progress. Checked by liveness_signal_handler. */
static volatile sig_atomic_t progress_indicator = 1;
/* Set to 1 if an error occurs in the signal handler. */
static volatile sig_atomic_t error_indicator = 0;
static void
sigusr1_handler (int signo)
{
sigusr1_received = 1;
/* Perform a fork with a trivial subprocess. */
pid_t pid = _Fork ();
if (pid == -1)
{
write_message ("error: fork\n");
error_indicator = 1;
return;
}
if (pid == 0)
_exit (0);
int status;
int ret = TEMP_FAILURE_RETRY (waitpid (pid, &status, 0));
if (ret < 0)
{
write_message ("error: waitpid\n");
error_indicator = 1;
return;
}
if (status != 0)
{
write_message ("error: unexpected exit status from subprocess\n");
error_indicator = 1;
return;
}
}
static void
liveness_signal_handler (int signo)
{
if (progress_indicator)
progress_indicator = 0;
else
write_message ("warning: thread seems to be stuck\n");
}
struct signal_send_args
{
pthread_t target;
int signo;
bool sleep;
};
#define SIGNAL_SEND_GET_ARG(arg, field) \
(((struct signal_send_args *)(arg))->field)
/* Send SIGNO to the parent thread. If SLEEP, wait a second between
signals, otherwise use barriers to delay sending signals. */
static void *
signal_sender (void *args)
{
int signo = SIGNAL_SEND_GET_ARG (args, signo);
bool sleep = SIGNAL_SEND_GET_ARG (args, sleep);
pthread_t target = SIGNAL_SEND_GET_ARG (args, target);
while (true)
{
if (!sleep)
xpthread_barrier_wait (&barrier);
xpthread_kill (target, signo);
if (sleep)
usleep (1 * 1000 * 1000);
else
xpthread_barrier_wait (&barrier);
}
return NULL;
}
static pthread_t sigusr1_sender[5];
static pthread_t sigusr2_sender;
static int
do_test (void)
{
xsignal (SIGUSR1, sigusr1_handler);
xsignal (SIGUSR2, liveness_signal_handler);
pthread_t self = pthread_self ();
struct signal_send_args sigusr2_args = { self, SIGUSR2, true };
sigusr2_sender = xpthread_create (NULL, signal_sender, &sigusr2_args);
/* Send SIGUSR1 signals from several threads. Hopefully, one
signal will hit one of the critical functions. Use a barrier to
avoid sending signals while not running fork/free/malloc. */
struct signal_send_args sigusr1_args = { self, SIGUSR1, false };
xpthread_barrier_init (&barrier, NULL,
array_length (sigusr1_sender) + 1);
for (size_t i = 0; i < array_length (sigusr1_sender); ++i)
sigusr1_sender[i] = xpthread_create (NULL, signal_sender, &sigusr1_args);
void *objects[malloc_objects] = {};
unsigned int fork_signals = 0;
unsigned int free_signals = 0;
unsigned int malloc_signals = 0;
unsigned int seed = 1;
for (int i = 0; i < iterations; ++i)
{
progress_indicator = 1;
int slot = rand_r (&seed) % malloc_objects;
size_t size = rand_r (&seed) % malloc_maximum_size;
/* Occasionally do a fork first, to catch deadlocks there as
well (see bug 24161). */
bool do_fork = (rand_r (&seed) % 7) == 0;
xpthread_barrier_wait (&barrier);
if (do_fork)
{
sigusr1_received = 0;
pid_t pid = _Fork ();
TEST_VERIFY_EXIT (pid != -1);
if (sigusr1_received)
++fork_signals;
if (pid == 0)
_exit (0);
int status;
int ret = TEMP_FAILURE_RETRY (waitpid (pid, &status, 0));
if (ret < 0)
FAIL_EXIT1 ("waitpid: %m");
TEST_COMPARE (status, 0);
}
sigusr1_received = 0;
free (objects[slot]);
if (sigusr1_received)
++free_signals;
sigusr1_received = 0;
objects[slot] = malloc (size);
if (sigusr1_received)
++malloc_signals;
xpthread_barrier_wait (&barrier);
if (objects[slot] == NULL || error_indicator != 0)
{
printf ("error: malloc: %m\n");
return 1;
}
}
/* Clean up allocations. */
for (int slot = 0; slot < malloc_objects; ++slot)
free (objects[slot]);
printf ("info: signals received during fork: %u\n", fork_signals);
printf ("info: signals received during free: %u\n", free_signals);
printf ("info: signals received during malloc: %u\n", malloc_signals);
return 0;
}
#define TIMEOUT 100
#include <support/test-driver.c>