1/* Copyright (C) 2002-2018 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#ifdef ARCH_FORK
135 pid = ARCH_FORK ();
136#else
137# error "ARCH_FORK must be defined so that the CLONE_SETTID flag is used"
138 pid = INLINE_SYSCALL (fork, 0);
139#endif
140
141
142 if (pid == 0)
143 {
144 struct pthread *self = THREAD_SELF;
145
146 /* See __pthread_once. */
147 if (__fork_generation_pointer != NULL)
148 *__fork_generation_pointer += __PTHREAD_ONCE_FORK_GEN_INCR;
149
150#if HP_TIMING_AVAIL
151 /* The CPU clock of the thread and process have to be set to zero. */
152 hp_timing_t now;
153 HP_TIMING_NOW (now);
154 THREAD_SETMEM (self, cpuclock_offset, now);
155 GL(dl_cpuclock_offset) = now;
156#endif
157
158#ifdef __NR_set_robust_list
159 /* Initialize the robust mutex list setting in the kernel which has
160 been reset during the fork. We do not check for errors because if
161 it fails here, it must have failed at process startup as well and
162 nobody could have used robust mutexes.
163 Before we do that, we have to clear the list of robust mutexes
164 because we do not inherit ownership of mutexes from the parent.
165 We do not have to set self->robust_head.futex_offset since we do
166 inherit the correct value from the parent. We do not need to clear
167 the pending operation because it must have been zero when fork was
168 called. */
169# if __PTHREAD_MUTEX_HAVE_PREV
170 self->robust_prev = &self->robust_head;
171# endif
172 self->robust_head.list = &self->robust_head;
173# ifdef SHARED
174 if (__builtin_expect (__libc_pthread_functions_init, 0))
175 PTHFCT_CALL (ptr_set_robust, (self));
176# else
177 extern __typeof (__nptl_set_robust) __nptl_set_robust
178 __attribute__((weak));
179 if (__builtin_expect (__nptl_set_robust != NULL, 0))
180 __nptl_set_robust (self);
181# endif
182#endif
183
184 /* Reset the lock state in the multi-threaded case. */
185 if (multiple_threads)
186 {
187 /* Release malloc locks. */
188 call_function_static_weak (__malloc_fork_unlock_child);
189
190 /* Reset the file list. These are recursive mutexes. */
191 fresetlockfiles ();
192
193 /* Reset locks in the I/O code. */
194 _IO_list_resetlock ();
195 }
196
197 /* Reset the lock the dynamic loader uses to protect its data. */
198 __rtld_lock_initialize (GL(dl_load_lock));
199
200 /* Run the handlers registered for the child. */
201 while (allp != NULL)
202 {
203 if (allp->handler->child_handler != NULL)
204 allp->handler->child_handler ();
205
206 /* Note that we do not have to wake any possible waiter.
207 This is the only thread in the new process. The count
208 may have been bumped up by other threads doing a fork.
209 We reset it to 1, to avoid waiting for non-existing
210 thread(s) to release the count. */
211 allp->handler->refcntr = 1;
212
213 /* XXX We could at this point look through the object pool
214 and mark all objects not on the __fork_handlers list as
215 unused. This is necessary in case the fork() happened
216 while another thread called dlclose() and that call had
217 to create a new list. */
218
219 allp = allp->next;
220 }
221
222 /* Initialize the fork lock. */
223 __fork_lock = LLL_LOCK_INITIALIZER;
224 }
225 else
226 {
227 /* Release acquired locks in the multi-threaded case. */
228 if (multiple_threads)
229 {
230 /* Release malloc locks, parent process variant. */
231 call_function_static_weak (__malloc_fork_unlock_parent);
232
233 /* We execute this even if the 'fork' call failed. */
234 _IO_list_unlock ();
235 }
236
237 /* Run the handlers registered for the parent. */
238 while (allp != NULL)
239 {
240 if (allp->handler->parent_handler != NULL)
241 allp->handler->parent_handler ();
242
243 if (atomic_decrement_and_test (&allp->handler->refcntr)
244 && allp->handler->need_signal)
245 futex_wake (&allp->handler->refcntr, 1, FUTEX_PRIVATE);
246
247 allp = allp->next;
248 }
249 }
250
251 return pid;
252}
253weak_alias (__libc_fork, __fork)
254libc_hidden_def (__fork)
255weak_alias (__libc_fork, fork)
256