1/* Copyright (C) 2002-2017 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <stdlib.h>
21#include <unistd.h>
22#include <sys/types.h>
23#include <sysdep.h>
24#include <libio/libioP.h>
25#include <tls.h>
26#include <hp-timing.h>
27#include <ldsodefs.h>
28#include <stdio-lock.h>
29#include <atomic.h>
30#include <nptl/pthreadP.h>
31#include <fork.h>
32#include <arch-fork.h>
33#include <futex-internal.h>
34#include <malloc/malloc-internal.h>
35
36static void
37fresetlockfiles (void)
38{
39 _IO_ITER i;
40
41 for (i = _IO_iter_begin(); i != _IO_iter_end(); i = _IO_iter_next(i))
42 if ((_IO_iter_file (i)->_flags & _IO_USER_LOCK) == 0)
43 _IO_lock_init (*((_IO_lock_t *) _IO_iter_file(i)->_lock));
44}
45
46
47pid_t
48__libc_fork (void)
49{
50 pid_t pid;
51 struct used_handler
52 {
53 struct fork_handler *handler;
54 struct used_handler *next;
55 } *allp = NULL;
56
57 /* Determine if we are running multiple threads. We skip some fork
58 handlers in the single-thread case, to make fork safer to use in
59 signal handlers. POSIX requires that fork is async-signal-safe,
60 but our current fork implementation is not. */
61 bool multiple_threads = THREAD_GETMEM (THREAD_SELF, header.multiple_threads);
62
63 /* Run all the registered preparation handlers. In reverse order.
64 While doing this we build up a list of all the entries. */
65 struct fork_handler *runp;
66 while ((runp = __fork_handlers) != NULL)
67 {
68 /* Make sure we read from the current RUNP pointer. */
69 atomic_full_barrier ();
70
71 unsigned int oldval = runp->refcntr;
72
73 if (oldval == 0)
74 /* This means some other thread removed the list just after
75 the pointer has been loaded. Try again. Either the list
76 is empty or we can retry it. */
77 continue;
78
79 /* Bump the reference counter. */
80 if (atomic_compare_and_exchange_bool_acq (&__fork_handlers->refcntr,
81 oldval + 1, oldval))
82 /* The value changed, try again. */
83 continue;
84
85 /* We bumped the reference counter for the first entry in the
86 list. That means that none of the following entries will
87 just go away. The unloading code works in the order of the
88 list.
89
90 While executing the registered handlers we are building a
91 list of all the entries so that we can go backward later on. */
92 while (1)
93 {
94 /* Execute the handler if there is one. */
95 if (runp->prepare_handler != NULL)
96 runp->prepare_handler ();
97
98 /* Create a new element for the list. */
99 struct used_handler *newp
100 = (struct used_handler *) alloca (sizeof (*newp));
101 newp->handler = runp;
102 newp->next = allp;
103 allp = newp;
104
105 /* Advance to the next handler. */
106 runp = runp->next;
107 if (runp == NULL)
108 break;
109
110 /* Bump the reference counter for the next entry. */
111 atomic_increment (&runp->refcntr);
112 }
113
114 /* We are done. */
115 break;
116 }
117
118 /* If we are not running multiple threads, we do not have to
119 preserve lock state. If fork runs from a signal handler, only
120 async-signal-safe functions can be used in the child. These data
121 structures are only used by unsafe functions, so their state does
122 not matter if fork was called from a signal handler. */
123 if (multiple_threads)
124 {
125 _IO_list_lock ();
126
127 /* Acquire malloc locks. This needs to come last because fork
128 handlers may use malloc, and the libio list lock has an
129 indirect malloc dependency as well (via the getdelim
130 function). */
131 call_function_static_weak (__malloc_fork_lock_parent);
132 }
133
134#ifndef NDEBUG
135 pid_t ppid = THREAD_GETMEM (THREAD_SELF, tid);
136#endif
137
138#ifdef ARCH_FORK
139 pid = ARCH_FORK ();
140#else
141# error "ARCH_FORK must be defined so that the CLONE_SETTID flag is used"
142 pid = INLINE_SYSCALL (fork, 0);
143#endif
144
145
146 if (pid == 0)
147 {
148 struct pthread *self = THREAD_SELF;
149
150 assert (THREAD_GETMEM (self, tid) != ppid);
151
152 /* See __pthread_once. */
153 if (__fork_generation_pointer != NULL)
154 *__fork_generation_pointer += __PTHREAD_ONCE_FORK_GEN_INCR;
155
156#if HP_TIMING_AVAIL
157 /* The CPU clock of the thread and process have to be set to zero. */
158 hp_timing_t now;
159 HP_TIMING_NOW (now);
160 THREAD_SETMEM (self, cpuclock_offset, now);
161 GL(dl_cpuclock_offset) = now;
162#endif
163
164#ifdef __NR_set_robust_list
165 /* Initialize the robust mutex list setting in the kernel which has
166 been reset during the fork. We do not check for errors because if
167 it fails here, it must have failed at process startup as well and
168 nobody could have used robust mutexes.
169 Before we do that, we have to clear the list of robust mutexes
170 because we do not inherit ownership of mutexes from the parent.
171 We do not have to set self->robust_head.futex_offset since we do
172 inherit the correct value from the parent. We do not need to clear
173 the pending operation because it must have been zero when fork was
174 called. */
175# ifdef __PTHREAD_MUTEX_HAVE_PREV
176 self->robust_prev = &self->robust_head;
177# endif
178 self->robust_head.list = &self->robust_head;
179# ifdef SHARED
180 if (__builtin_expect (__libc_pthread_functions_init, 0))
181 PTHFCT_CALL (ptr_set_robust, (self));
182# else
183 extern __typeof (__nptl_set_robust) __nptl_set_robust
184 __attribute__((weak));
185 if (__builtin_expect (__nptl_set_robust != NULL, 0))
186 __nptl_set_robust (self);
187# endif
188#endif
189
190 /* Reset the lock state in the multi-threaded case. */
191 if (multiple_threads)
192 {
193 /* Release malloc locks. */
194 call_function_static_weak (__malloc_fork_unlock_child);
195
196 /* Reset the file list. These are recursive mutexes. */
197 fresetlockfiles ();
198
199 /* Reset locks in the I/O code. */
200 _IO_list_resetlock ();
201 }
202
203 /* Reset the lock the dynamic loader uses to protect its data. */
204 __rtld_lock_initialize (GL(dl_load_lock));
205
206 /* Run the handlers registered for the child. */
207 while (allp != NULL)
208 {
209 if (allp->handler->child_handler != NULL)
210 allp->handler->child_handler ();
211
212 /* Note that we do not have to wake any possible waiter.
213 This is the only thread in the new process. The count
214 may have been bumped up by other threads doing a fork.
215 We reset it to 1, to avoid waiting for non-existing
216 thread(s) to release the count. */
217 allp->handler->refcntr = 1;
218
219 /* XXX We could at this point look through the object pool
220 and mark all objects not on the __fork_handlers list as
221 unused. This is necessary in case the fork() happened
222 while another thread called dlclose() and that call had
223 to create a new list. */
224
225 allp = allp->next;
226 }
227
228 /* Initialize the fork lock. */
229 __fork_lock = LLL_LOCK_INITIALIZER;
230 }
231 else
232 {
233 assert (THREAD_GETMEM (THREAD_SELF, tid) == ppid);
234
235 /* Release acquired locks in the multi-threaded case. */
236 if (multiple_threads)
237 {
238 /* Release malloc locks, parent process variant. */
239 call_function_static_weak (__malloc_fork_unlock_parent);
240
241 /* We execute this even if the 'fork' call failed. */
242 _IO_list_unlock ();
243 }
244
245 /* Run the handlers registered for the parent. */
246 while (allp != NULL)
247 {
248 if (allp->handler->parent_handler != NULL)
249 allp->handler->parent_handler ();
250
251 if (atomic_decrement_and_test (&allp->handler->refcntr)
252 && allp->handler->need_signal)
253 futex_wake (&allp->handler->refcntr, 1, FUTEX_PRIVATE);
254
255 allp = allp->next;
256 }
257 }
258
259 return pid;
260}
261weak_alias (__libc_fork, __fork)
262libc_hidden_def (__fork)
263weak_alias (__libc_fork, fork)
264