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glibc/sysdeps/nptl/fork.c
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/* Copyright (C) 2002-2015 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 <stdio-lock.h> | |
#include <atomic.h> | |
#include <nptl/pthreadP.h> | |
#include <fork.h> | |
#include <arch-fork.h> | |
#include <futex-internal.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) | |
futex_wake (&allp->handler->refcntr, 1, FUTEX_PRIVATE); | |
allp = allp->next; | |
} | |
} | |
return pid; | |
} | |
weak_alias (__libc_fork, __fork) | |
libc_hidden_def (__fork) | |
weak_alias (__libc_fork, fork) |