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glibc.7805
malloc-fork-deadlock.patch
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File malloc-fork-deadlock.patch of Package glibc.7805
2016-05-04 Florian Weimer <fweimer@redhat.com> * malloc/malloc-internal.h: Adjust header file guard. 2016-04-14 Florian Weimer <fweimer@redhat.com> * malloc/arena.c (__malloc_fork_lock_parent) (__malloc_fork_unlock_parent, __malloc_fork_unlock_child): Add internal_function attribute. 2016-04-14 Florian Weimer <fweimer@redhat.com> Remove malloc hooks from fork handler. They are no longer needed because malloc runs right before fork, and no malloc calls from other fork handlers are not possible anymore. * malloc/malloc.c (malloc_atfork, free_atfork): Remove declarations. * malloc/arena.c (save_malloc_hook, save_free_hook, save_arena) (ATFORK_ARENA_PTR, malloc_atfork, free_atfork) (atfork_recursive_cntr): Remove. (__malloc_fork_lock_parent): Do not override malloc hooks and thread_arena. (__malloc_fork_unlock_parent): Do not restore malloc hooks and thread_arena. (__malloc_fork_unlock_child): Do not restore malloc hooks. Use thread_arena instead of save_arena. 2016-04-14 Florian Weimer <fweimer@redhat.com> [BZ #19431] Run the malloc fork handler as late as possible to avoid deadlocks. * malloc/malloc-internal.h: New file. * malloc/malloc.c: Include it. * malloc/arena.c (ATFORK_MEM): Remove. (__malloc_fork_lock_parent): Rename from ptmalloc_lock_all. Update comment. (__malloc_fork_unlock_parent): Rename from ptmalloc_unlock_all. (__malloc_fork_unlock_child): Rename from ptmalloc_unlock_all2. Remove outdated comment. (ptmalloc_init): Do not call thread_atfork. Remove thread_atfork_static. * malloc/tst-malloc-fork-deadlock.c: New file. * Makefile (tests): Add tst-malloc-fork-deadlock. (tst-malloc-fork-deadlock): Link against libpthread. * manual/memory.texi (Aligned Memory Blocks): Update safety annotation comments. * sysdeps/nptl/fork.c (__libc_fork): Call __malloc_fork_lock_parent, __malloc_fork_unlock_parent, __malloc_fork_unlock_child. * sysdeps/mach/hurd/fork.c (__fork): Likewise. 2016-02-19 Florian Weimer <fweimer@redhat.com> * sysdeps/generic/malloc-machine.h: Assume mutex_init is always available. Do not define NO_THREADS. * malloc/malloc.c: Do not check NO_THREADS. * malloc/arena.c: Likewise. Index: glibc-2.22/malloc/Makefile =================================================================== --- glibc-2.22.orig/malloc/Makefile +++ glibc-2.22/malloc/Makefile @@ -28,7 +28,8 @@ tests := mallocbug tst-malloc tst-valloc 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-thread-exit + tst-malloc-backtrace tst-malloc-thread-exit \ + tst-malloc-fork-deadlock test-srcs = tst-mtrace routines = malloc morecore mcheck mtrace obstack \ @@ -49,6 +50,8 @@ $(objpfx)tst-malloc-backtrace: $(common- $(common-objpfx)nptl/libpthread_nonshared.a $(objpfx)tst-malloc-thread-exit: $(common-objpfx)nptl/libpthread.so \ $(common-objpfx)nptl/libpthread_nonshared.a +$(objpfx)tst-malloc-fork-deadlock: $(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 Index: glibc-2.22/malloc/arena.c =================================================================== --- glibc-2.22.orig/malloc/arena.c +++ glibc-2.22/malloc/arena.c @@ -128,149 +128,43 @@ int __malloc_initialized = -1; /**************************************************************************/ -#ifndef NO_THREADS - /* atfork support. */ -static void *(*save_malloc_hook)(size_t __size, const void *); -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. */ - -# define ATFORK_ARENA_PTR ((void *) -1) - -/* The following hooks are used while the `atfork' handling mechanism - is active. */ - -static void * -malloc_atfork (size_t sz, const void *caller) -{ - void *vptr = NULL; - void *victim; - - tsd_getspecific (arena_key, vptr); - if (vptr == ATFORK_ARENA_PTR) - { - /* We are the only thread that may allocate at all. */ - if (save_malloc_hook != malloc_check) - { - return _int_malloc (&main_arena, sz); - } - else - { - if (top_check () < 0) - return 0; +/* 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. */ - victim = _int_malloc (&main_arena, sz + 1); - return mem2mem_check (victim, sz); - } - } - else - { - /* Suspend the thread until the `atfork' handlers have completed. - By that time, the hooks will have been reset as well, so that - mALLOc() can be used again. */ - (void) mutex_lock (&list_lock); - (void) mutex_unlock (&list_lock); - return __libc_malloc (sz); - } -} - -static void -free_atfork (void *mem, const void *caller) -{ - void *vptr = NULL; - mstate ar_ptr; - mchunkptr p; /* chunk corresponding to mem */ - - if (mem == 0) /* free(0) has no effect */ - return; - - p = mem2chunk (mem); /* do not bother to replicate free_check here */ - - if (chunk_is_mmapped (p)) /* release mmapped memory. */ - { - munmap_chunk (p); - return; - } - - ar_ptr = arena_for_chunk (p); - tsd_getspecific (arena_key, vptr); - _int_free (ar_ptr, p, vptr == ATFORK_ARENA_PTR); -} - - -/* 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). */ - -static void -ptmalloc_lock_all (void) +void +internal_function +__malloc_fork_lock_parent (void) { - mstate ar_ptr; - if (__malloc_initialized < 1) 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)) - { - void *my_arena; - tsd_getspecific (arena_key, my_arena); - if (my_arena == ATFORK_ARENA_PTR) - /* This is the same thread which already locks the global list. - Just bump the counter. */ - goto out; + (void) mutex_lock (&list_lock); - /* This thread has to wait its turn. */ - (void) mutex_lock (&list_lock); - } - for (ar_ptr = &main_arena;; ) + for (mstate ar_ptr = &main_arena;; ) { (void) mutex_lock (&ar_ptr->mutex); ar_ptr = ar_ptr->next; if (ar_ptr == &main_arena) break; } - save_malloc_hook = __malloc_hook; - save_free_hook = __free_hook; - __malloc_hook = malloc_atfork; - __free_hook = free_atfork; - /* Only the current thread may perform malloc/free calls now. */ - tsd_getspecific (arena_key, save_arena); - tsd_setspecific (arena_key, ATFORK_ARENA_PTR); -out: - ++atfork_recursive_cntr; } -static void -ptmalloc_unlock_all (void) +void +internal_function +__malloc_fork_unlock_parent (void) { - mstate ar_ptr; - if (__malloc_initialized < 1) return; - if (--atfork_recursive_cntr != 0) - return; - - tsd_setspecific (arena_key, save_arena); - __malloc_hook = save_malloc_hook; - __free_hook = save_free_hook; - for (ar_ptr = &main_arena;; ) + for (mstate ar_ptr = &main_arena;; ) { (void) mutex_unlock (&ar_ptr->mutex); ar_ptr = ar_ptr->next; @@ -280,35 +174,26 @@ 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 +internal_function +__malloc_fork_unlock_child (void) { - mstate ar_ptr; - if (__malloc_initialized < 1) return; - tsd_setspecific (arena_key, save_arena); - __malloc_hook = save_malloc_hook; - __free_hook = save_free_hook; + void *vptr = NULL; + mstate current_arena = tsd_getspecific (arena_key, vptr); - /* Push all arenas to the free list, except save_arena, which is + /* Push all arenas to the free list, except thread_arena, which is attached to the current thread. */ mutex_init (&free_list_lock); - if (save_arena != NULL) - ((mstate) save_arena)->attached_threads = 1; + if (current_arena != NULL) + current_arena->attached_threads = 1; free_list = NULL; - for (ar_ptr = &main_arena;; ) + for (mstate ar_ptr = &main_arena;; ) { mutex_init (&ar_ptr->mutex); - if (ar_ptr != save_arena) + if (ar_ptr != current_arena) { /* This arena is no longer attached to any thread. */ ar_ptr->attached_threads = 0; @@ -321,15 +206,8 @@ ptmalloc_unlock_all2 (void) } mutex_init (&list_lock); - atfork_recursive_cntr = 0; } -# else - -# define ptmalloc_unlock_all2 ptmalloc_unlock_all -# endif -#endif /* !NO_THREADS */ - /* Initialization routine. */ #include <string.h> extern char **_environ; @@ -399,7 +277,6 @@ 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)) { @@ -474,14 +351,6 @@ 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 @@ -831,7 +700,8 @@ _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: glibc-2.22/malloc/malloc-internal.h =================================================================== --- /dev/null +++ glibc-2.22/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_INTERNAL_H +#define _MALLOC_INTERNAL_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_INTERNAL_H */ Index: glibc-2.22/malloc/malloc.c =================================================================== --- glibc-2.22.orig/malloc/malloc.c +++ glibc-2.22/malloc/malloc.c @@ -244,6 +244,7 @@ /* For ALIGN_UP. */ #include <libc-internal.h> +#include <malloc/malloc-internal.h> /* Debugging: @@ -1074,10 +1075,6 @@ static void* realloc_check(void* oldme const void *caller); static void* memalign_check(size_t alignment, size_t bytes, const void *caller); -#ifndef NO_THREADS -static void* malloc_atfork(size_t sz, const void *caller); -static void free_atfork(void* mem, const void *caller); -#endif /* ------------------ MMAP support ------------------ */ Index: glibc-2.22/malloc/tst-malloc-fork-deadlock.c =================================================================== --- /dev/null +++ glibc-2.22/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: glibc-2.22/manual/memory.texi =================================================================== --- glibc-2.22.orig/manual/memory.texi +++ glibc-2.22/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: glibc-2.22/sysdeps/generic/malloc-machine.h =================================================================== --- glibc-2.22.orig/sysdeps/generic/malloc-machine.h +++ glibc-2.22/sysdeps/generic/malloc-machine.h @@ -22,30 +22,9 @@ #include <atomic.h> -#ifndef mutex_init /* No threads, provide dummy macros */ +#ifndef mutex_init -# define NO_THREADS - -/* The mutex functions used to do absolutely nothing, i.e. lock, - trylock and unlock would always just return 0. However, even - without any concurrently active threads, a mutex can be used - legitimately as an `in use' flag. To make the code that is - protected by a mutex async-signal safe, these macros would have to - be based on atomic test-and-set operations, for example. */ -typedef int mutex_t; - -# define mutex_init(m) (*(m) = 0) -# define mutex_lock(m) ({ *(m) = 1; 0; }) -# define mutex_trylock(m) (*(m) ? 1 : ((*(m) = 1), 0)) -# define mutex_unlock(m) (*(m) = 0) -# define MUTEX_INITIALIZER (0) - -typedef void *tsd_key_t; -# define tsd_key_create(key, destr) do {} while(0) -# define tsd_setspecific(key, data) ((key) = (data)) -# define tsd_getspecific(key, vptr) (vptr = (key)) - -# define thread_atfork(prepare, parent, child) do {} while(0) +#error NO_THREADS no longer supported #endif /* !defined mutex_init */ Index: glibc-2.22/sysdeps/mach/hurd/fork.c =================================================================== --- glibc-2.22.orig/sysdeps/mach/hurd/fork.c +++ glibc-2.22/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: glibc-2.22/sysdeps/nptl/fork.c =================================================================== --- glibc-2.22.orig/sysdeps/nptl/fork.c +++ glibc-2.22/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 (); @@ -210,6 +218,9 @@ __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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