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malloc: Fix attached thread reference count handling [BZ #19243]

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reused_arena can increase the attached thread count of arenas on the
free list.  This means that the assertion that the reference count is
zero is incorrect.  In this case, the reference count initialization
is incorrect as well and could cause arenas to be put on the free
list too early (while they still have attached threads).

	* malloc/arena.c (get_free_list): Remove assert and adjust
	reference count handling.  Add comment about reused_arena
	interaction.
	(reused_arena): Add comments abount get_free_list interaction.
	* malloc/tst-malloc-thread-exit.c: New file.
	* malloc/Makefile (tests): Add tst-malloc-thread-exit.
	(tst-malloc-thread-exit): Link against libpthread.
This commit is contained in:
Florian Weimer 2015-12-16 12:39:48 +01:00
parent f1aceee392
commit 3da825ce48
4 changed files with 239 additions and 5 deletions
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11
ChangeLog
View File

@ -1,3 +1,14 @@
2015-12-16 Florian Weimer <fweimer@redhat.com>
[BZ #19243]
* malloc/arena.c (get_free_list): Remove assert and adjust
reference count handling. Add comment about reused_arena
interaction.
(reused_arena): Add comments abount get_free_list interaction.
* malloc/tst-malloc-thread-exit.c: New file.
* malloc/Makefile (tests): Add tst-malloc-thread-exit.
(tst-malloc-thread-exit): Link against libpthread.
2015-12-15 H.J. Lu <hongjiu.lu@intel.com>
[BZ #19367]

4
malloc/Makefile
View File

@ -28,7 +28,7 @@ tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
tst-mallocstate tst-mcheck tst-mallocfork tst-trim1 \
tst-malloc-usable tst-realloc tst-posix_memalign \
tst-pvalloc tst-memalign tst-mallopt tst-scratch_buffer \
tst-malloc-backtrace
tst-malloc-backtrace tst-malloc-thread-exit
test-srcs = tst-mtrace
routines = malloc morecore mcheck mtrace obstack \
@ -47,6 +47,8 @@ libmemusage-inhibit-o = $(filter-out .os,$(object-suffixes))
$(objpfx)tst-malloc-backtrace: $(common-objpfx)nptl/libpthread.so \
$(common-objpfx)nptl/libpthread_nonshared.a
$(objpfx)tst-malloc-thread-exit: $(common-objpfx)nptl/libpthread.so \
$(common-objpfx)nptl/libpthread_nonshared.a
# These should be removed by `make clean'.
extra-objs = mcheck-init.o libmcheck.a

12
malloc/arena.c
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@ -805,6 +805,8 @@ _int_new_arena (size_t size)
}
/* Remove an arena from free_list. The arena may be in use because it
was attached concurrently to a thread by reused_arena below. */
static mstate
get_free_list (void)
{
@ -818,10 +820,8 @@ get_free_list (void)
{
free_list = result->next_free;
/* Arenas on the free list are not attached to any thread. */
assert (result->attached_threads == 0);
/* But the arena will now be attached to this thread. */
result->attached_threads = 1;
/* The arena will be attached to this thread. */
++result->attached_threads;
detach_arena (replaced_arena);
}
@ -849,6 +849,8 @@ reused_arena (mstate avoid_arena)
if (next_to_use == NULL)
next_to_use = &main_arena;
/* Iterate over all arenas (including those linked from
free_list). */
result = next_to_use;
do
{
@ -883,6 +885,8 @@ reused_arena (mstate avoid_arena)
(void) mutex_lock (&result->mutex);
out:
/* Attach the arena to the current thread. Note that we may have
selected an arena which was on free_list. */
{
mstate replaced_arena = thread_arena;
(void) mutex_lock (&list_lock);

217
malloc/tst-malloc-thread-exit.c Normal file
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@ -0,0 +1,217 @@
/* Test malloc with concurrent thread termination.
Copyright (C) 2015 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
<http://www.gnu.org/licenses/>. */
/* This thread spawns a number of outer threads, equal to the arena
limit. The outer threads run a loop which start and join two
different kinds of threads: the first kind allocates (attaching an
arena to the thread; malloc_first_thread) and waits, the second
kind waits and allocates (wait_first_threads). Both kinds of
threads exit immediately after waiting. The hope is that this will
exhibit races in thread termination and arena management,
particularly related to the arena free list. */
#include <errno.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define TIMEOUT 7
static bool termination_requested;
static int inner_thread_count = 4;
static size_t malloc_size = 32;
static void
__attribute__ ((noinline, noclone))
unoptimized_free (void *ptr)
{
free (ptr);
}
static void *
malloc_first_thread (void * closure)
{
pthread_barrier_t *barrier = closure;
void *ptr = malloc (malloc_size);
if (ptr == NULL)
{
printf ("error: malloc: %m\n");
abort ();
}
int ret = pthread_barrier_wait (barrier);
if (ret != 0 && ret != PTHREAD_BARRIER_SERIAL_THREAD)
{
errno = ret;
printf ("error: pthread_barrier_wait: %m\n");
abort ();
}
unoptimized_free (ptr);
return NULL;
}
static void *
wait_first_thread (void * closure)
{
pthread_barrier_t *barrier = closure;
int ret = pthread_barrier_wait (barrier);
if (ret != 0 && ret != PTHREAD_BARRIER_SERIAL_THREAD)
{
errno = ret;
printf ("error: pthread_barrier_wait: %m\n");
abort ();
}
void *ptr = malloc (malloc_size);
if (ptr == NULL)
{
printf ("error: malloc: %m\n");
abort ();
}
unoptimized_free (ptr);
return NULL;
}
static void *
outer_thread (void *closure)
{
pthread_t *threads = calloc (sizeof (*threads), inner_thread_count);
if (threads == NULL)
{
printf ("error: calloc: %m\n");
abort ();
}
while (!__atomic_load_n (&termination_requested, __ATOMIC_RELAXED))
{
pthread_barrier_t barrier;
int ret = pthread_barrier_init (&barrier, NULL, inner_thread_count + 1);
if (ret != 0)
{
errno = ret;
printf ("pthread_barrier_init: %m\n");
abort ();
}
for (int i = 0; i < inner_thread_count; ++i)
{
void *(*func) (void *);
if ((i % 2) == 0)
func = malloc_first_thread;
else
func = wait_first_thread;
ret = pthread_create (threads + i, NULL, func, &barrier);
if (ret != 0)
{
errno = ret;
printf ("error: pthread_create: %m\n");
abort ();
}
}
ret = pthread_barrier_wait (&barrier);
if (ret != 0 && ret != PTHREAD_BARRIER_SERIAL_THREAD)
{
errno = ret;
printf ("pthread_wait: %m\n");
abort ();
}
for (int i = 0; i < inner_thread_count; ++i)
{
ret = pthread_join (threads[i], NULL);
if (ret != 0)
{
ret = errno;
printf ("error: pthread_join: %m\n");
abort ();
}
}
ret = pthread_barrier_destroy (&barrier);
if (ret != 0)
{
ret = errno;
printf ("pthread_barrier_destroy: %m\n");
abort ();
}
}
free (threads);
return NULL;
}
static int
do_test (void)
{
/* The number of top-level threads should be equal to the number of
arenas. See arena_get2. */
long outer_thread_count = sysconf (_SC_NPROCESSORS_ONLN);
if (outer_thread_count >= 1)
{
/* See NARENAS_FROM_NCORES in malloc.c. */
if (sizeof (long) == 4)
outer_thread_count *= 2;
else
outer_thread_count *= 8;
}
/* Leave some room for shutting down all threads gracefully. */
int timeout = TIMEOUT - 2;
pthread_t *threads = calloc (sizeof (*threads), outer_thread_count);
if (threads == NULL)
{
printf ("error: calloc: %m\n");
abort ();
}
for (long i = 0; i < outer_thread_count; ++i)
{
int ret = pthread_create (threads + i, NULL, outer_thread, NULL);
if (ret != 0)
{
errno = ret;
printf ("error: pthread_create: %m\n");
abort ();
}
}
struct timespec ts = {timeout, 0};
if (nanosleep (&ts, NULL))
{
printf ("error: error: nanosleep: %m\n");
abort ();
}
__atomic_store_n (&termination_requested, true, __ATOMIC_RELAXED);
for (long i = 0; i < outer_thread_count; ++i)
{
int ret = pthread_join (threads[i], NULL);
if (ret != 0)
{
errno = ret;
printf ("error: pthread_join: %m\n");
abort ();
}
}
free (threads);
return 0;
}
#define TEST_FUNCTION do_test ()
#include "../test-skeleton.c"