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c3f1918b6c
glibc/glibc-rh1332917-2.patch
Florian Weimer c3f1918b6c Resolves: #1332917 
Fix deadlock between between fflush, getdelim, and fork
2016-05-06 21:07:01 +02:00

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commit 29d794863cd6e03115d3670707cc873a9965ba92
Author: Florian Weimer <fweimer@redhat.com>
Date: Thu Apr 14 09:17:02 2016 +0200
malloc: Run fork handler as late as possible [BZ #19431]
Previously, a thread M invoking fork would acquire locks in this order:
(M1) malloc arena locks (in the registered fork handler)
(M2) libio list lock
A thread F invoking flush (NULL) would acquire locks in this order:
(F1) libio list lock
(F2) individual _IO_FILE locks
A thread G running getdelim would use this order:
(G1) _IO_FILE lock
(G2) malloc arena lock
After executing (M1), (F1), (G1), none of the threads can make progress.
This commit changes the fork lock order to:
(M'1) libio list lock
(M'2) malloc arena locks
It explicitly encodes the lock order in the implementations of fork,
and does not rely on the registration order, thus avoiding the deadlock.
Index: b/malloc/arena.c
===================================================================
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -141,10 +141,6 @@ static void *(*save_malloc_hook)(size_t
static void (*save_free_hook) (void *__ptr, const void *);
static void *save_arena;
-# ifdef ATFORK_MEM
-ATFORK_MEM;
-# endif
-
/* Magic value for the thread-specific arena pointer when
malloc_atfork() is in use. */
@@ -214,14 +210,14 @@ free_atfork (void *mem, const void *call
/* Counter for number of times the list is locked by the same thread. */
static unsigned int atfork_recursive_cntr;
-/* The following two functions are registered via thread_atfork() to
- make sure that the mutexes remain in a consistent state in the
- fork()ed version of a thread. Also adapt the malloc and free hooks
- temporarily, because the `atfork' handler mechanism may use
- malloc/free internally (e.g. in LinuxThreads). */
+/* The following three functions are called around fork from a
+ multi-threaded process. We do not use the general fork handler
+ mechanism to make sure that our handlers are the last ones being
+ called, so that other fork handlers can use the malloc
+ subsystem. */
-static void
-ptmalloc_lock_all (void)
+void
+__malloc_fork_lock_parent (void)
{
mstate ar_ptr;
@@ -229,7 +225,7 @@ ptmalloc_lock_all (void)
return;
/* We do not acquire free_list_lock here because we completely
- reconstruct free_list in ptmalloc_unlock_all2. */
+ reconstruct free_list in __malloc_fork_unlock_child. */
if (mutex_trylock (&list_lock))
{
@@ -256,7 +252,7 @@ ptmalloc_lock_all (void)
__free_hook = free_atfork;
/* Only the current thread may perform malloc/free calls now.
save_arena will be reattached to the current thread, in
- ptmalloc_lock_all, so save_arena->attached_threads is not
+ __malloc_fork_lock_parent, so save_arena->attached_threads is not
updated. */
tsd_getspecific (arena_key, save_arena);
tsd_setspecific (arena_key, ATFORK_ARENA_PTR);
@@ -264,8 +260,8 @@ out:
++atfork_recursive_cntr;
}
-static void
-ptmalloc_unlock_all (void)
+void
+__malloc_fork_unlock_parent (void)
{
mstate ar_ptr;
@@ -276,8 +272,8 @@ ptmalloc_unlock_all (void)
return;
/* Replace ATFORK_ARENA_PTR with save_arena.
- save_arena->attached_threads was not changed in ptmalloc_lock_all
- and is still correct. */
+ save_arena->attached_threads was not changed in
+ __malloc_fork_lock_parent and is still correct. */
tsd_setspecific (arena_key, save_arena);
__malloc_hook = save_malloc_hook;
__free_hook = save_free_hook;
@@ -291,15 +287,8 @@ ptmalloc_unlock_all (void)
(void) mutex_unlock (&list_lock);
}
-# ifdef __linux__
-
-/* In NPTL, unlocking a mutex in the child process after a
- fork() is currently unsafe, whereas re-initializing it is safe and
- does not leak resources. Therefore, a special atfork handler is
- installed for the child. */
-
-static void
-ptmalloc_unlock_all2 (void)
+void
+__malloc_fork_unlock_child (void)
{
mstate ar_ptr;
@@ -335,11 +324,6 @@ ptmalloc_unlock_all2 (void)
atfork_recursive_cntr = 0;
}
-# else
-
-# define ptmalloc_unlock_all2 ptmalloc_unlock_all
-# endif
-
/* Initialization routine. */
#include <string.h>
extern char **_environ;
@@ -409,7 +393,6 @@ ptmalloc_init (void)
tsd_key_create (&arena_key, NULL);
tsd_setspecific (arena_key, (void *) &main_arena);
- thread_atfork (ptmalloc_lock_all, ptmalloc_unlock_all, ptmalloc_unlock_all2);
const char *s = NULL;
if (__glibc_likely (_environ != NULL))
{
@@ -484,14 +467,6 @@ ptmalloc_init (void)
__malloc_initialized = 1;
}
-/* There are platforms (e.g. Hurd) with a link-time hook mechanism. */
-#ifdef thread_atfork_static
-thread_atfork_static (ptmalloc_lock_all, ptmalloc_unlock_all, \
- ptmalloc_unlock_all2)
-#endif
-
-
-
/* Managing heaps and arenas (for concurrent threads) */
#if MALLOC_DEBUG > 1
@@ -838,7 +813,8 @@ _int_new_arena (size_t size)
limit is reached). At this point, some arena has to be attached
to two threads. We could acquire the arena lock before list_lock
to make it less likely that reused_arena picks this new arena,
- but this could result in a deadlock with ptmalloc_lock_all. */
+ but this could result in a deadlock with
+ __malloc_fork_lock_parent. */
(void) mutex_lock (&a->mutex);
Index: b/malloc/malloc-internal.h
===================================================================
--- /dev/null
+++ b/malloc/malloc-internal.h
@@ -0,0 +1,32 @@
+/* Internal declarations for malloc, for use within libc.
+ Copyright (C) 2016 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 <http://www.gnu.org/licenses/>. */
+
+#ifndef _MALLOC_PRIVATE_H
+#define _MALLOC_PRIVATE_H
+
+/* Called in the parent process before a fork. */
+void __malloc_fork_lock_parent (void) internal_function attribute_hidden;
+
+/* Called in the parent process after a fork. */
+void __malloc_fork_unlock_parent (void) internal_function attribute_hidden;
+
+/* Called in the child process after a fork. */
+void __malloc_fork_unlock_child (void) internal_function attribute_hidden;
+
+
+#endif /* _MALLOC_PRIVATE_H */
Index: b/malloc/malloc.c
===================================================================
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -244,6 +244,7 @@
/* For ALIGN_UP. */
#include <libc-internal.h>
+#include <malloc/malloc-internal.h>
/*
Debugging:
Index: b/malloc/tst-malloc-fork-deadlock.c
===================================================================
--- /dev/null
+++ b/malloc/tst-malloc-fork-deadlock.c
@@ -0,0 +1,220 @@
+/* Test concurrent fork, getline, and fflush (NULL).
+ Copyright (C) 2016 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 <http://www.gnu.org/licenses/>. */
+
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <time.h>
+#include <string.h>
+#include <signal.h>
+
+static int do_test (void);
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
+
+enum {
+ /* Number of threads which call fork. */
+ fork_thread_count = 4,
+ /* Number of threads which call getline (and, indirectly,
+ malloc). */
+ read_thread_count = 8,
+};
+
+static bool termination_requested;
+
+static void *
+fork_thread_function (void *closure)
+{
+ while (!__atomic_load_n (&termination_requested, __ATOMIC_RELAXED))
+ {
+ pid_t pid = fork ();
+ if (pid < 0)
+ {
+ printf ("error: fork: %m\n");
+ abort ();
+ }
+ else if (pid == 0)
+ _exit (17);
+
+ int status;
+ if (waitpid (pid, &status, 0) < 0)
+ {
+ printf ("error: waitpid: %m\n");
+ abort ();
+ }
+ if (!WIFEXITED (status) || WEXITSTATUS (status) != 17)
+ {
+ printf ("error: waitpid returned invalid status: %d\n", status);
+ abort ();
+ }
+ }
+ return NULL;
+}
+
+static char *file_to_read;
+
+static void *
+read_thread_function (void *closure)
+{
+ FILE *f = fopen (file_to_read, "r");
+ if (f == NULL)
+ {
+ printf ("error: fopen (%s): %m\n", file_to_read);
+ abort ();
+ }
+
+ while (!__atomic_load_n (&termination_requested, __ATOMIC_RELAXED))
+ {
+ rewind (f);
+ char *line = NULL;
+ size_t line_allocated = 0;
+ ssize_t ret = getline (&line, &line_allocated, f);
+ if (ret < 0)
+ {
+ printf ("error: getline: %m\n");
+ abort ();
+ }
+ free (line);
+ }
+ fclose (f);
+
+ return NULL;
+}
+
+static void *
+flushall_thread_function (void *closure)
+{
+ while (!__atomic_load_n (&termination_requested, __ATOMIC_RELAXED))
+ if (fflush (NULL) != 0)
+ {
+ printf ("error: fflush (NULL): %m\n");
+ abort ();
+ }
+ return NULL;
+}
+
+static void
+create_threads (pthread_t *threads, size_t count, void *(*func) (void *))
+{
+ for (size_t i = 0; i < count; ++i)
+ {
+ int ret = pthread_create (threads + i, NULL, func, NULL);
+ if (ret != 0)
+ {
+ errno = ret;
+ printf ("error: pthread_create: %m\n");
+ abort ();
+ }
+ }
+}
+
+static void
+join_threads (pthread_t *threads, size_t count)
+{
+ for (size_t i = 0; i < count; ++i)
+ {
+ int ret = pthread_join (threads[i], NULL);
+ if (ret != 0)
+ {
+ errno = ret;
+ printf ("error: pthread_join: %m\n");
+ abort ();
+ }
+ }
+}
+
+/* Create a file which consists of a single long line, and assigns
+ file_to_read. The hope is that this triggers an allocation in
+ getline which needs a lock. */
+static void
+create_file_with_large_line (void)
+{
+ int fd = create_temp_file ("bug19431-large-line", &file_to_read);
+ if (fd < 0)
+ {
+ printf ("error: create_temp_file: %m\n");
+ abort ();
+ }
+ FILE *f = fdopen (fd, "w+");
+ if (f == NULL)
+ {
+ printf ("error: fdopen: %m\n");
+ abort ();
+ }
+ for (int i = 0; i < 50000; ++i)
+ fputc ('x', f);
+ fputc ('\n', f);
+ if (ferror (f))
+ {
+ printf ("error: fputc: %m\n");
+ abort ();
+ }
+ if (fclose (f) != 0)
+ {
+ printf ("error: fclose: %m\n");
+ abort ();
+ }
+}
+
+static int
+do_test (void)
+{
+ /* Make sure that we do not exceed the arena limit with the number
+ of threads we configured. */
+ if (mallopt (M_ARENA_MAX, 400) == 0)
+ {
+ printf ("error: mallopt (M_ARENA_MAX) failed\n");
+ return 1;
+ }
+
+ /* Leave some room for shutting down all threads gracefully. */
+ int timeout = 3;
+ if (timeout > TIMEOUT)
+ timeout = TIMEOUT - 1;
+
+ create_file_with_large_line ();
+
+ pthread_t fork_threads[fork_thread_count];
+ create_threads (fork_threads, fork_thread_count, fork_thread_function);
+ pthread_t read_threads[read_thread_count];
+ create_threads (read_threads, read_thread_count, read_thread_function);
+ pthread_t flushall_threads[1];
+ create_threads (flushall_threads, 1, flushall_thread_function);
+
+ struct timespec ts = {timeout, 0};
+ if (nanosleep (&ts, NULL))
+ {
+ printf ("error: error: nanosleep: %m\n");
+ abort ();
+ }
+
+ __atomic_store_n (&termination_requested, true, __ATOMIC_RELAXED);
+
+ join_threads (flushall_threads, 1);
+ join_threads (read_threads, read_thread_count);
+ join_threads (fork_threads, fork_thread_count);
+
+ free (file_to_read);
+
+ return 0;
+}
Index: b/manual/memory.texi
===================================================================
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -1055,14 +1055,6 @@ systems that do not support @w{ISO C11}.
@c _dl_addr_inside_object ok
@c determine_info ok
@c __rtld_lock_unlock_recursive (dl_load_lock) @aculock
-@c thread_atfork @asulock @aculock @acsfd @acsmem
-@c __register_atfork @asulock @aculock @acsfd @acsmem
-@c lll_lock (__fork_lock) @asulock @aculock
-@c fork_handler_alloc @asulock @aculock @acsfd @acsmem
-@c calloc dup @asulock @aculock @acsfd @acsmem
-@c __linkin_atfork ok
-@c catomic_compare_and_exchange_bool_acq ok
-@c lll_unlock (__fork_lock) @aculock
@c *_environ @mtsenv
@c next_env_entry ok
@c strcspn dup ok
Index: b/sysdeps/mach/hurd/fork.c
===================================================================
--- a/sysdeps/mach/hurd/fork.c
+++ b/sysdeps/mach/hurd/fork.c
@@ -26,6 +26,7 @@
#include <assert.h>
#include "hurdmalloc.h" /* XXX */
#include <tls.h>
+#include <malloc/malloc-internal.h>
#undef __fork
@@ -107,6 +108,12 @@ __fork (void)
/* Run things that prepare for forking before we create the task. */
RUN_HOOK (_hurd_fork_prepare_hook, ());
+ /* Acquire malloc locks. This needs to come last because fork
+ handlers may use malloc, and the libio list lock has an
+ indirect malloc dependency as well (via the getdelim
+ function). */
+ __malloc_fork_lock_parent ();
+
/* Lock things that want to be locked before we fork. */
{
void *const *p;
@@ -608,6 +615,9 @@ __fork (void)
nthreads * sizeof (*threads));
}
+ /* Release malloc locks. */
+ __malloc_fork_unlock_parent ();
+
/* Run things that want to run in the parent to restore it to
normality. Usually prepare hooks and parent hooks are
symmetrical: the prepare hook arrests state in some way for the
@@ -659,6 +669,9 @@ __fork (void)
/* Forking clears the trace flag. */
__sigemptyset (&_hurdsig_traced);
+ /* Release malloc locks. */
+ __malloc_fork_unlock_child ();
+
/* Run things that want to run in the child task to set up. */
RUN_HOOK (_hurd_fork_child_hook, ());
Index: b/sysdeps/nptl/fork.c
===================================================================
--- a/sysdeps/nptl/fork.c
+++ b/sysdeps/nptl/fork.c
@@ -31,7 +31,7 @@
#include <fork.h>
#include <arch-fork.h>
#include <futex-internal.h>
-
+#include <malloc/malloc-internal.h>
static void
fresetlockfiles (void)
@@ -111,6 +111,11 @@ __libc_fork (void)
_IO_list_lock ();
+ /* Acquire malloc locks. This needs to come last because fork
+ handlers may use malloc, and the libio list lock has an indirect
+ malloc dependency as well (via the getdelim function). */
+ __malloc_fork_lock_parent ();
+
#ifndef NDEBUG
pid_t ppid = THREAD_GETMEM (THREAD_SELF, tid);
#endif
@@ -168,6 +173,9 @@ __libc_fork (void)
# endif
#endif
+ /* Release malloc locks. */
+ __malloc_fork_unlock_child ();
+
/* Reset the file list. These are recursive mutexes. */
fresetlockfiles ();
@@ -209,6 +217,9 @@ __libc_fork (void)
/* Restore the PID value. */
THREAD_SETMEM (THREAD_SELF, pid, parentpid);
+ /* Release malloc locks, parent process variant. */
+ __malloc_fork_unlock_parent ();
+
/* We execute this even if the 'fork' call failed. */
_IO_list_unlock ();
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