1/* Copyright (C) 2002-2016 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
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 /* Run all the registered preparation handlers. In reverse order.
58 While doing this we build up a list of all the entries. */
59 struct fork_handler *runp;
60 while ((runp = __fork_handlers) != NULL)
61 {
62 /* Make sure we read from the current RUNP pointer. */
63 atomic_full_barrier ();
64
65 unsigned int oldval = runp->refcntr;
66
67 if (oldval == 0)
68 /* This means some other thread removed the list just after
69 the pointer has been loaded. Try again. Either the list
70 is empty or we can retry it. */
71 continue;
72
73 /* Bump the reference counter. */
74 if (atomic_compare_and_exchange_bool_acq (&__fork_handlers->refcntr,
75 oldval + 1, oldval))
76 /* The value changed, try again. */
77 continue;
78
79 /* We bumped the reference counter for the first entry in the
80 list. That means that none of the following entries will
81 just go away. The unloading code works in the order of the
82 list.
83
84 While executing the registered handlers we are building a
85 list of all the entries so that we can go backward later on. */
86 while (1)
87 {
88 /* Execute the handler if there is one. */
89 if (runp->prepare_handler != NULL)
90 runp->prepare_handler ();
91
92 /* Create a new element for the list. */
93 struct used_handler *newp
94 = (struct used_handler *) alloca (sizeof (*newp));
95 newp->handler = runp;
96 newp->next = allp;
97 allp = newp;
98
99 /* Advance to the next handler. */
100 runp = runp->next;
101 if (runp == NULL)
102 break;
103
104 /* Bump the reference counter for the next entry. */
105 atomic_increment (&runp->refcntr);
106 }
107
108 /* We are done. */
109 break;
110 }
111
112 _IO_list_lock ();
113
114#ifndef NDEBUG
115 pid_t ppid = THREAD_GETMEM (THREAD_SELF, tid);
116#endif
117
118 /* We need to prevent the getpid() code to update the PID field so
119 that, if a signal arrives in the child very early and the signal
120 handler uses getpid(), the value returned is correct. */
121 pid_t parentpid = THREAD_GETMEM (THREAD_SELF, pid);
122 THREAD_SETMEM (THREAD_SELF, pid, -parentpid);
123
124#ifdef ARCH_FORK
125 pid = ARCH_FORK ();
126#else
127# error "ARCH_FORK must be defined so that the CLONE_SETTID flag is used"
128 pid = INLINE_SYSCALL (fork, 0);
129#endif
130
131
132 if (pid == 0)
133 {
134 struct pthread *self = THREAD_SELF;
135
136 assert (THREAD_GETMEM (self, tid) != ppid);
137
138 /* See __pthread_once. */
139 if (__fork_generation_pointer != NULL)
140 *__fork_generation_pointer += __PTHREAD_ONCE_FORK_GEN_INCR;
141
142 /* Adjust the PID field for the new process. */
143 THREAD_SETMEM (self, pid, THREAD_GETMEM (self, tid));
144
145#if HP_TIMING_AVAIL
146 /* The CPU clock of the thread and process have to be set to zero. */
147 hp_timing_t now;
148 HP_TIMING_NOW (now);
149 THREAD_SETMEM (self, cpuclock_offset, now);
150 GL(dl_cpuclock_offset) = now;
151#endif
152
153#ifdef __NR_set_robust_list
154 /* Initialize the robust mutex list which has been reset during
155 the fork. We do not check for errors since if it fails here
156 it failed at process start as well and noone could have used
157 robust mutexes. We also do not have to set
158 self->robust_head.futex_offset since we inherit the correct
159 value from the parent. */
160# ifdef SHARED
161 if (__builtin_expect (__libc_pthread_functions_init, 0))
162 PTHFCT_CALL (ptr_set_robust, (self));
163# else
164 extern __typeof (__nptl_set_robust) __nptl_set_robust
165 __attribute__((weak));
166 if (__builtin_expect (__nptl_set_robust != NULL, 0))
167 __nptl_set_robust (self);
168# endif
169#endif
170
171 /* Reset the file list. These are recursive mutexes. */
172 fresetlockfiles ();
173
174 /* Reset locks in the I/O code. */
175 _IO_list_resetlock ();
176
177 /* Reset the lock the dynamic loader uses to protect its data. */
178 __rtld_lock_initialize (GL(dl_load_lock));
179
180 /* Run the handlers registered for the child. */
181 while (allp != NULL)
182 {
183 if (allp->handler->child_handler != NULL)
184 allp->handler->child_handler ();
185
186 /* Note that we do not have to wake any possible waiter.
187 This is the only thread in the new process. The count
188 may have been bumped up by other threads doing a fork.
189 We reset it to 1, to avoid waiting for non-existing
190 thread(s) to release the count. */
191 allp->handler->refcntr = 1;
192
193 /* XXX We could at this point look through the object pool
194 and mark all objects not on the __fork_handlers list as
195 unused. This is necessary in case the fork() happened
196 while another thread called dlclose() and that call had
197 to create a new list. */
198
199 allp = allp->next;
200 }
201
202 /* Initialize the fork lock. */
203 __fork_lock = LLL_LOCK_INITIALIZER;
204 }
205 else
206 {
207 assert (THREAD_GETMEM (THREAD_SELF, tid) == ppid);
208
209 /* Restore the PID value. */
210 THREAD_SETMEM (THREAD_SELF, pid, parentpid);
211
212 /* We execute this even if the 'fork' call failed. */
213 _IO_list_unlock ();
214
215 /* Run the handlers registered for the parent. */
216 while (allp != NULL)
217 {
218 if (allp->handler->parent_handler != NULL)
219 allp->handler->parent_handler ();
220
221 if (atomic_decrement_and_test (&allp->handler->refcntr)
222 && allp->handler->need_signal)
223 futex_wake (&allp->handler->refcntr, 1, FUTEX_PRIVATE);
224
225 allp = allp->next;
226 }
227 }
228
229 return pid;
230}
231weak_alias (__libc_fork, __fork)
232libc_hidden_def (__fork)
233weak_alias (__libc_fork, fork)
234