about summary refs log tree commit diff
path: root/sysdeps/nptl/fork.c
blob: dfd11698b923143e04c62051453091783c3fd50b (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
/* Copyright (C) 2002-2014 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

   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; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sysdep.h>
#include <libio/libioP.h>
#include <tls.h>
#include <hp-timing.h>
#include <ldsodefs.h>
#include <bits/stdio-lock.h>
#include <atomic.h>
#include <nptl/pthreadP.h>
#include <fork.h>
#include <arch-fork.h>


static void
fresetlockfiles (void)
{
  _IO_ITER i;

  for (i = _IO_iter_begin(); i != _IO_iter_end(); i = _IO_iter_next(i))
    if ((_IO_iter_file (i)->_flags & _IO_USER_LOCK) == 0)
      _IO_lock_init (*((_IO_lock_t *) _IO_iter_file(i)->_lock));
}


pid_t
__libc_fork (void)
{
  pid_t pid;
  struct used_handler
  {
    struct fork_handler *handler;
    struct used_handler *next;
  } *allp = NULL;

  /* Run all the registered preparation handlers.  In reverse order.
     While doing this we build up a list of all the entries.  */
  struct fork_handler *runp;
  while ((runp = __fork_handlers) != NULL)
    {
      /* Make sure we read from the current RUNP pointer.  */
      atomic_full_barrier ();

      unsigned int oldval = runp->refcntr;

      if (oldval == 0)
	/* This means some other thread removed the list just after
	   the pointer has been loaded.  Try again.  Either the list
	   is empty or we can retry it.  */
	continue;

      /* Bump the reference counter.  */
      if (atomic_compare_and_exchange_bool_acq (&__fork_handlers->refcntr,
						oldval + 1, oldval))
	/* The value changed, try again.  */
	continue;

      /* We bumped the reference counter for the first entry in the
	 list.  That means that none of the following entries will
	 just go away.  The unloading code works in the order of the
	 list.

	 While executing the registered handlers we are building a
	 list of all the entries so that we can go backward later on.  */
      while (1)
	{
	  /* Execute the handler if there is one.  */
	  if (runp->prepare_handler != NULL)
	    runp->prepare_handler ();

	  /* Create a new element for the list.  */
	  struct used_handler *newp
	    = (struct used_handler *) alloca (sizeof (*newp));
	  newp->handler = runp;
	  newp->next = allp;
	  allp = newp;

	  /* Advance to the next handler.  */
	  runp = runp->next;
	  if (runp == NULL)
	    break;

	  /* Bump the reference counter for the next entry.  */
	  atomic_increment (&runp->refcntr);
	}

      /* We are done.  */
      break;
    }

  _IO_list_lock ();

#ifndef NDEBUG
  pid_t ppid = THREAD_GETMEM (THREAD_SELF, tid);
#endif

  /* We need to prevent the getpid() code to update the PID field so
     that, if a signal arrives in the child very early and the signal
     handler uses getpid(), the value returned is correct.  */
  pid_t parentpid = THREAD_GETMEM (THREAD_SELF, pid);
  THREAD_SETMEM (THREAD_SELF, pid, -parentpid);

#ifdef ARCH_FORK
  pid = ARCH_FORK ();
#else
# error "ARCH_FORK must be defined so that the CLONE_SETTID flag is used"
  pid = INLINE_SYSCALL (fork, 0);
#endif


  if (pid == 0)
    {
      struct pthread *self = THREAD_SELF;

      assert (THREAD_GETMEM (self, tid) != ppid);

      /* See __pthread_once.  */
      if (__fork_generation_pointer != NULL)
	*__fork_generation_pointer += __PTHREAD_ONCE_FORK_GEN_INCR;

      /* Adjust the PID field for the new process.  */
      THREAD_SETMEM (self, pid, THREAD_GETMEM (self, tid));

#if HP_TIMING_AVAIL
      /* The CPU clock of the thread and process have to be set to zero.  */
      hp_timing_t now;
      HP_TIMING_NOW (now);
      THREAD_SETMEM (self, cpuclock_offset, now);
      GL(dl_cpuclock_offset) = now;
#endif

#ifdef __NR_set_robust_list
      /* Initialize the robust mutex list which has been reset during
	 the fork.  We do not check for errors since if it fails here
	 it failed at process start as well and noone could have used
	 robust mutexes.  We also do not have to set
	 self->robust_head.futex_offset since we inherit the correct
	 value from the parent.  */
# ifdef SHARED
      if (__builtin_expect (__libc_pthread_functions_init, 0))
	PTHFCT_CALL (ptr_set_robust, (self));
# else
      extern __typeof (__nptl_set_robust) __nptl_set_robust
	__attribute__((weak));
      if (__builtin_expect (__nptl_set_robust != NULL, 0))
	__nptl_set_robust (self);
# endif
#endif

      /* Reset the file list.  These are recursive mutexes.  */
      fresetlockfiles ();

      /* Reset locks in the I/O code.  */
      _IO_list_resetlock ();

      /* Reset the lock the dynamic loader uses to protect its data.  */
      __rtld_lock_initialize (GL(dl_load_lock));

      /* Run the handlers registered for the child.  */
      while (allp != NULL)
	{
	  if (allp->handler->child_handler != NULL)
	    allp->handler->child_handler ();

	  /* Note that we do not have to wake any possible waiter.
	     This is the only thread in the new process.  The count
	     may have been bumped up by other threads doing a fork.
	     We reset it to 1, to avoid waiting for non-existing
	     thread(s) to release the count.  */
	  allp->handler->refcntr = 1;

	  /* XXX We could at this point look through the object pool
	     and mark all objects not on the __fork_handlers list as
	     unused.  This is necessary in case the fork() happened
	     while another thread called dlclose() and that call had
	     to create a new list.  */

	  allp = allp->next;
	}

      /* Initialize the fork lock.  */
      __fork_lock = LLL_LOCK_INITIALIZER;
    }
  else
    {
      assert (THREAD_GETMEM (THREAD_SELF, tid) == ppid);

      /* Restore the PID value.  */
      THREAD_SETMEM (THREAD_SELF, pid, parentpid);

      /* We execute this even if the 'fork' call failed.  */
      _IO_list_unlock ();

      /* Run the handlers registered for the parent.  */
      while (allp != NULL)
	{
	  if (allp->handler->parent_handler != NULL)
	    allp->handler->parent_handler ();

	  if (atomic_decrement_and_test (&allp->handler->refcntr)
	      && allp->handler->need_signal)
	    lll_futex_wake (allp->handler->refcntr, 1, LLL_PRIVATE);

	  allp = allp->next;
	}
    }

  return pid;
}
weak_alias (__libc_fork, __fork)
libc_hidden_def (__fork)
weak_alias (__libc_fork, fork)