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stdlib: Allow concurrent quick_exit (BZ 31997)

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As for exit, also allows concurrent quick_exit to avoid race
conditions when it is called concurrently.  Since it uses the same
internal function as exit, the __exit_lock lock is moved to
__run_exit_handlers.  It also solved a potential concurrent when
calling exit and quick_exit concurrently.

The test case 'expected' is expanded to a value larger than the
minimum required by C/POSIX (32 entries) so at_quick_exit() will
require libc to allocate a new block.  This makes the test mre likely to
trigger concurrent issues (through free() at __run_exit_handlers)
if quick_exit() interacts with the at_quick_exit list concurrently.

This is also the latest interpretation of the Austin Ticket [1].

Checked on x86_64-linux-gnu.

[1] https://austingroupbugs.net/view.php?id=1845
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Adhemerval Zanella 2024-08-05 11:27:35 -03:00
parent 5097cd344f
commit c6af8a9a3c
5 changed files with 196 additions and 146 deletions
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1
stdlib/Makefile
View File

@ -274,6 +274,7 @@ tests := \
tst-bz20544 \
tst-canon-bz26341 \
tst-concurrent-exit \
tst-concurrent-quick_exit \
tst-cxa_atexit \
tst-environ \
tst-getrandom \

18
stdlib/exit.c
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@ -28,6 +28,13 @@
__exit_funcs_lock is declared. */
bool __exit_funcs_done = false;
/* The lock handles concurrent exit() and quick_exit(), even though the
C/POSIX standard states that calling exit() more than once is UB. The
recursive lock allows atexit() handlers or destructors to call exit()
itself. In this case, the handler list execution will resume at the
point of the current handler. */
__libc_lock_define_initialized_recursive (static, __exit_lock)
/* Call all functions registered with `atexit' and `on_exit',
in the reverse of the order in which they were registered
perform stdio cleanup, and terminate program execution with STATUS. */
@ -36,6 +43,9 @@ attribute_hidden
__run_exit_handlers (int status, struct exit_function_list **listp,
bool run_list_atexit, bool run_dtors)
{
/* The exit should never return, so there is no need to unlock it. */
__libc_lock_lock_recursive (__exit_lock);
/* First, call the TLS destructors. */
if (run_dtors)
call_function_static_weak (__call_tls_dtors);
@ -132,17 +142,9 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
}
/* The lock handles concurrent exit(), even though the C/POSIX standard states
that calling exit() more than once is UB. The recursive lock allows
atexit() handlers or destructors to call exit() itself. In this case, the
handler list execution will resume at the point of the current handler. */
__libc_lock_define_initialized_recursive (static, __exit_lock)
void
exit (int status)
{
/* The exit should never return, so there is no need to unlock it. */
__libc_lock_lock_recursive (__exit_lock);
__run_exit_handlers (status, &__exit_funcs, true, true);
}
libc_hidden_def (exit)

160
stdlib/tst-concurrent-exit-skeleton.c Normal file
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@ -0,0 +1,160 @@
/* Check if exit/quick_exit can be called concurrently by multiple threads.
Copyright (C) 2024 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; if not, see
<https://www.gnu.org/licenses/>. */
#include <array_length.h>
#include <stdlib.h>
#include <support/check.h>
#include <support/xthread.h>
#include <stdio.h>
#include <support/xunistd.h>
#include <string.h>
/* A value larger than the minimum required by C/POSIX (32), to trigger a
new block memory allocation. */
#define MAX_atexit 64
static pthread_barrier_t barrier;
static void *
tf (void *closure)
{
xpthread_barrier_wait (&barrier);
EXIT (0);
return NULL;
}
static const char expected[] = "00000000000000000000000000000000000"
"00000000000000000000003021121130211";
static char crumbs[sizeof (expected)];
static int next_slot = 0;
static void
exit_with_flush (int code)
{
fflush (stdout);
/* glibc allows recursive EXIT, the ATEXIT handlers execution will be
resumed from the where the previous EXIT was interrupted. */
EXIT (code);
}
/* Take some time, so another thread potentially issue EXIT. */
#define SETUP_NANOSLEEP \
if (nanosleep (&(struct timespec) { .tv_sec = 0, .tv_nsec = 1000L }, \
NULL) != 0) \
FAIL_EXIT1 ("nanosleep: %m")
static void
fn0 (void)
{
crumbs[next_slot++] = '0';
SETUP_NANOSLEEP;
}
static void
fn1 (void)
{
crumbs[next_slot++] = '1';
SETUP_NANOSLEEP;
}
static void
fn2 (void)
{
crumbs[next_slot++] = '2';
ATEXIT (fn1);
SETUP_NANOSLEEP;
}
static void
fn3 (void)
{
crumbs[next_slot++] = '3';
ATEXIT (fn2);
ATEXIT (fn0);
SETUP_NANOSLEEP;
}
static void
fn_final (void)
{
TEST_COMPARE_STRING (crumbs, expected);
exit_with_flush (0);
}
_Noreturn static void
child (void)
{
enum { nthreads = 8 };
xpthread_barrier_init (&barrier, NULL, nthreads + 1);
pthread_t thr[nthreads];
for (int i = 0; i < nthreads; i++)
thr[i] = xpthread_create (NULL, tf, NULL);
xpthread_barrier_wait (&barrier);
for (int i = 0; i < nthreads; i++)
{
pthread_join (thr[i], NULL);
/* It should not be reached, it means that thread did not exit for
some reason. */
support_record_failure ();
}
EXIT (2);
}
static int
do_test (void)
{
/* Register a large number of handler that will trigger a heap allocation
for the handle state. On EXIT, each block will be freed after the
handle is processed. */
int slots_remaining = MAX_atexit;
/* Register this first so it can verify expected order of the rest. */
ATEXIT (fn_final); --slots_remaining;
TEST_VERIFY_EXIT (ATEXIT (fn1) == 0); --slots_remaining;
TEST_VERIFY_EXIT (ATEXIT (fn3) == 0); --slots_remaining;
TEST_VERIFY_EXIT (ATEXIT (fn1) == 0); --slots_remaining;
TEST_VERIFY_EXIT (ATEXIT (fn2) == 0); --slots_remaining;
TEST_VERIFY_EXIT (ATEXIT (fn1) == 0); --slots_remaining;
TEST_VERIFY_EXIT (ATEXIT (fn3) == 0); --slots_remaining;
while (slots_remaining > 0)
{
TEST_VERIFY_EXIT (ATEXIT (fn0) == 0); --slots_remaining;
}
pid_t pid = xfork ();
if (pid != 0)
{
int status;
xwaitpid (pid, &status, 0);
TEST_VERIFY (WIFEXITED (status));
}
else
child ();
return 0;
}
#include <support/test-driver.c>

141
stdlib/tst-concurrent-exit.c
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@ -16,142 +16,7 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <array_length.h>
#include <stdlib.h>
#include <support/check.h>
#include <support/xthread.h>
#include <stdio.h>
#include <support/xunistd.h>
#include <string.h>
#define EXIT(__r) exit (__r)
#define ATEXIT(__f) atexit (__f)
#define MAX_atexit 32
static pthread_barrier_t barrier;
static void *
tf (void *closure)
{
xpthread_barrier_wait (&barrier);
exit (0);
return NULL;
}
static const char expected[] = "00000000000000000000000003021121130211";
static char crumbs[sizeof (expected)];
static int next_slot = 0;
static void
exit_with_flush (int code)
{
fflush (stdout);
/* glibc allows recursive exit, the atexit handlers execution will be
resumed from the where the previous exit was interrupted. */
exit (code);
}
/* Take some time, so another thread potentially issue exit. */
#define SETUP_NANOSLEEP \
if (nanosleep (&(struct timespec) { .tv_sec = 0, .tv_nsec = 1000L }, \
NULL) != 0) \
FAIL_EXIT1 ("nanosleep: %m")
static void
fn0 (void)
{
crumbs[next_slot++] = '0';
SETUP_NANOSLEEP;
}
static void
fn1 (void)
{
crumbs[next_slot++] = '1';
SETUP_NANOSLEEP;
}
static void
fn2 (void)
{
crumbs[next_slot++] = '2';
atexit (fn1);
SETUP_NANOSLEEP;
}
static void
fn3 (void)
{
crumbs[next_slot++] = '3';
atexit (fn2);
atexit (fn0);
SETUP_NANOSLEEP;
}
static void
fn_final (void)
{
TEST_COMPARE_STRING (crumbs, expected);
exit_with_flush (0);
}
_Noreturn static void
child (void)
{
enum { nthreads = 8 };
xpthread_barrier_init (&barrier, NULL, nthreads + 1);
pthread_t thr[nthreads];
for (int i = 0; i < nthreads; i++)
thr[i] = xpthread_create (NULL, tf, NULL);
xpthread_barrier_wait (&barrier);
for (int i = 0; i < nthreads; i++)
{
pthread_join (thr[i], NULL);
/* It should not be reached, it means that thread did not exit for
some reason. */
support_record_failure ();
}
exit (2);
}
static int
do_test (void)
{
/* Register a large number of handler that will trigger a heap allocation
for the handle state. On exit, each block will be freed after the
handle is processed. */
int slots_remaining = MAX_atexit;
/* Register this first so it can verify expected order of the rest. */
atexit (fn_final); --slots_remaining;
TEST_VERIFY_EXIT (atexit (fn1) == 0); --slots_remaining;
TEST_VERIFY_EXIT (atexit (fn3) == 0); --slots_remaining;
TEST_VERIFY_EXIT (atexit (fn1) == 0); --slots_remaining;
TEST_VERIFY_EXIT (atexit (fn2) == 0); --slots_remaining;
TEST_VERIFY_EXIT (atexit (fn1) == 0); --slots_remaining;
TEST_VERIFY_EXIT (atexit (fn3) == 0); --slots_remaining;
while (slots_remaining > 0)
{
TEST_VERIFY_EXIT (atexit (fn0) == 0); --slots_remaining;
}
pid_t pid = xfork ();
if (pid != 0)
{
int status;
xwaitpid (pid, &status, 0);
TEST_VERIFY (WIFEXITED (status));
}
else
child ();
return 0;
}
#include <support/test-driver.c>
#include "tst-concurrent-exit-skeleton.c"

22
stdlib/tst-concurrent-quick_exit.c Normal file
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@ -0,0 +1,22 @@
/* Check if quick_exit can be called concurrently by multiple threads.
Copyright (C) 2024 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; if not, see
<https://www.gnu.org/licenses/>. */
#define EXIT(__r) quick_exit (__r)
#define ATEXIT(__f) at_quick_exit (__f)
#include "tst-concurrent-exit-skeleton.c"