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glibc/sysdeps/mach/hurd/fork.c

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/* Copyright (C) 1994-2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <unistd.h>
#include <hurd.h>
#include <hurd/signal.h>
#include <hurd/threadvar.h>
#include <setjmp.h>
#include <thread_state.h>
#include <sysdep.h> /* For stack growth direction. */
#include "set-hooks.h"
#include <assert.h>
#include "hurdmalloc.h" /* XXX */
#include <tls.h>
#include <malloc/malloc-internal.h>
#undef __fork
/* Things that want to be locked while forking. */
symbol_set_declare (_hurd_fork_locks)
/* Application callbacks registered through pthread_atfork. */
DEFINE_HOOK (_hurd_atfork_prepare_hook, (void));
DEFINE_HOOK (_hurd_atfork_child_hook, (void));
DEFINE_HOOK (_hurd_atfork_parent_hook, (void));
/* Things that want to be called before we fork, to prepare the parent for
task_create, when the new child task will inherit our address space. */
DEFINE_HOOK (_hurd_fork_prepare_hook, (void));
/* Things that want to be called when we are forking, with the above all
locked. They are passed the task port of the child. The child process
is all set up except for doing proc_child, and has no threads yet. */
DEFINE_HOOK (_hurd_fork_setup_hook, (void));
/* Things to be run in the child fork. */
DEFINE_HOOK (_hurd_fork_child_hook, (void));
/* Things to be run in the parent fork. */
DEFINE_HOOK (_hurd_fork_parent_hook, (void));
/* Clone the calling process, creating an exact copy.
Return -1 for errors, 0 to the new process,
and the process ID of the new process to the old process. */
pid_t
__fork (void)
{
jmp_buf env;
pid_t pid;
size_t i;
error_t err;
struct hurd_sigstate *volatile ss;
RUN_HOOK (_hurd_atfork_prepare_hook, ());
ss = _hurd_self_sigstate ();
__spin_lock (&ss->critical_section_lock);
#undef LOSE
#define LOSE do { assert_perror (err); goto lose; } while (0) /* XXX */
if (! setjmp (env))
{
process_t newproc;
task_t newtask;
thread_t thread, sigthread;
mach_port_urefs_t thread_refs, sigthread_refs;
struct machine_thread_state state;
mach_msg_type_number_t statecount;
mach_port_t *portnames = NULL;
mach_msg_type_number_t nportnames = 0;
mach_port_type_t *porttypes = NULL;
mach_msg_type_number_t nporttypes = 0;
thread_t *threads = NULL;
mach_msg_type_number_t nthreads = 0;
int ports_locked = 0, stopped = 0;
void resume_threads (void)
{
if (! stopped)
return;
assert (threads);
for (i = 0; i < nthreads; ++i)
if (threads[i] != ss->thread)
__thread_resume (threads[i]);
stopped = 0;
}
/* Run things that prepare for forking before we create the task. */
RUN_HOOK (_hurd_fork_prepare_hook, ());
/* Lock things that want to be locked before we fork. */
{
void *const *p;
for (p = symbol_set_first_element (_hurd_fork_locks);
! symbol_set_end_p (_hurd_fork_locks, p);
++p)
__mutex_lock (*p);
}
__mutex_lock (&_hurd_siglock);
/* Acquire malloc locks. This needs to come last because fork
handlers may use malloc, and the libio list lock has an
indirect malloc dependency as well (via the getdelim
function). */
call_function_static_weak (__malloc_fork_lock_parent);
_hurd_malloc_fork_prepare ();
newtask = MACH_PORT_NULL;
thread = sigthread = MACH_PORT_NULL;
newproc = MACH_PORT_NULL;
/* Lock all the port cells for the standard ports while we copy the
address space. We want to insert all the send rights into the
child with the same names. */
for (i = 0; i < _hurd_nports; ++i)
__spin_lock (&_hurd_ports[i].lock);
ports_locked = 1;
/* Keep our SS locked while stopping other threads, so they don't get a
chance to have it locked in the copied space. */
__spin_lock (&ss->lock);
/* Stop all other threads while copying the address space,
so nothing changes. */
err = __proc_dostop (_hurd_ports[INIT_PORT_PROC].port, ss->thread);
__spin_unlock (&ss->lock);
if (!err)
{
stopped = 1;
#define XXX_KERNEL_PAGE_FAULT_BUG /* XXX work around page fault bug in mk */
#ifdef XXX_KERNEL_PAGE_FAULT_BUG
/* Gag me with a pitchfork.
The bug scenario is this:
- The page containing __mach_task_self_ is paged out.
- The signal thread was faulting on that page when we
suspended it via proc_dostop. It holds some lock, or set
some busy bit, or somesuch.
- Now this thread faults on that same page.
- GRATUIOUS DEADLOCK
We can break the deadlock by aborting the thread that faulted
first, which if the bug happened was the signal thread because
it is the only other thread and we just suspended it.
*/
__thread_abort (_hurd_msgport_thread);
#endif
/* Create the child task. It will inherit a copy of our memory. */
err = __task_create (__mach_task_self (),
#ifdef KERN_INVALID_LEDGER
NULL, 0, /* OSF Mach */
#endif
1, &newtask);
}
/* Unlock the global signal state lock, so we do not
block the signal thread any longer than necessary. */
__mutex_unlock (&_hurd_siglock);
if (err)
LOSE;
/* Fetch the names of all ports used in this task. */
if (err = __mach_port_names (__mach_task_self (),
&portnames, &nportnames,
&porttypes, &nporttypes))
LOSE;
if (nportnames != nporttypes)
{
err = EGRATUITOUS;
LOSE;
}
/* Get send rights for all the threads in this task.
We want to avoid giving these rights to the child. */
if (err = __task_threads (__mach_task_self (), &threads, &nthreads))
LOSE;
/* Get the child process's proc server port. We will insert it into
the child with the same name as we use for our own proc server
port; and we will need it to set the child's message port. */
if (err = __proc_task2proc (_hurd_ports[INIT_PORT_PROC].port,
newtask, &newproc))
LOSE;
/* Insert all our port rights into the child task. */
thread_refs = sigthread_refs = 0;
for (i = 0; i < nportnames; ++i)
{
if (porttypes[i] & MACH_PORT_TYPE_RECEIVE)
{
/* This is a receive right. We want to give the child task
its own new receive right under the same name. */
if (err = __mach_port_allocate_name (newtask,
MACH_PORT_RIGHT_RECEIVE,
portnames[i]))
LOSE;
if (porttypes[i] & MACH_PORT_TYPE_SEND)
{
/* Give the child as many send rights for its receive
right as we have for ours. */
mach_port_urefs_t refs;
mach_port_t port;
mach_msg_type_name_t poly;
if (err = __mach_port_get_refs (__mach_task_self (),
portnames[i],
MACH_PORT_RIGHT_SEND,
&refs))
LOSE;
if (err = __mach_port_extract_right (newtask,
portnames[i],
MACH_MSG_TYPE_MAKE_SEND,
&port, &poly))
LOSE;
if (portnames[i] == _hurd_msgport)
{
/* We just created a receive right for the child's
message port and are about to insert send rights
for it. Now, while we happen to have a send right
for it, give it to the proc server. */
mach_port_t old;
if (err = __proc_setmsgport (newproc, port, &old))
LOSE;
if (old != MACH_PORT_NULL)
/* XXX what to do here? */
__mach_port_deallocate (__mach_task_self (), old);
/* The new task will receive its own exceptions
on its message port. */
if (err =
#ifdef TASK_EXCEPTION_PORT
__task_set_special_port (newtask,
TASK_EXCEPTION_PORT,
port)
#elif defined (EXC_MASK_ALL)
__task_set_exception_ports
(newtask, EXC_MASK_ALL & ~(EXC_MASK_SYSCALL
| EXC_MASK_MACH_SYSCALL
| EXC_MASK_RPC_ALERT),
port, EXCEPTION_DEFAULT, MACHINE_THREAD_STATE)
#else
# error task_set_exception_port?
#endif
)
LOSE;
}
if (err = __mach_port_insert_right (newtask,
portnames[i],
port,
MACH_MSG_TYPE_MOVE_SEND))
LOSE;
if (refs > 1
&& (err = __mach_port_mod_refs (newtask,
portnames[i],
MACH_PORT_RIGHT_SEND,
refs - 1)))
LOSE;
}
if (porttypes[i] & MACH_PORT_TYPE_SEND_ONCE)
{
/* Give the child a send-once right for its receive right,
since we have one for ours. */
mach_port_t port;
mach_msg_type_name_t poly;
if (err = __mach_port_extract_right
(newtask,
portnames[i],
MACH_MSG_TYPE_MAKE_SEND_ONCE,
&port, &poly))
LOSE;
if (err = __mach_port_insert_right
(newtask,
portnames[i], port,
MACH_MSG_TYPE_MOVE_SEND_ONCE))
LOSE;
}
}
else if (porttypes[i]
& (MACH_PORT_TYPE_SEND|MACH_PORT_TYPE_DEAD_NAME))
{
/* This is a send right or a dead name.
Give the child as many references for it as we have. */
mach_port_urefs_t refs = 0, *record_refs = NULL;
mach_port_t insert;
mach_msg_type_name_t insert_type = MACH_MSG_TYPE_COPY_SEND;
if (portnames[i] == newtask || portnames[i] == newproc)
/* Skip the name we use for the child's task or proc ports. */
continue;
if (portnames[i] == __mach_task_self ())
/* For the name we use for our own task port,
insert the child's task port instead. */
insert = newtask;
else if (portnames[i] == _hurd_ports[INIT_PORT_PROC].port)
{
/* Use the proc server port for the new task. */
insert = newproc;
insert_type = MACH_MSG_TYPE_COPY_SEND;
}
else if (portnames[i] == ss->thread)
{
/* For the name we use for our own thread port, we will
insert the thread port for the child main user thread
after we create it. */
insert = MACH_PORT_NULL;
record_refs = &thread_refs;
/* Allocate a dead name right for this name as a
placeholder, so the kernel will not chose this name
for any other new port (it might use it for one of the
rights created when a thread is created). */
if (err = __mach_port_allocate_name
(newtask, MACH_PORT_RIGHT_DEAD_NAME, portnames[i]))
LOSE;
}
else if (portnames[i] == _hurd_msgport_thread)
/* For the name we use for our signal thread's thread port,
we will insert the thread port for the child's signal
thread after we create it. */
{
insert = MACH_PORT_NULL;
record_refs = &sigthread_refs;
/* Allocate a dead name right as a placeholder. */
if (err = __mach_port_allocate_name
(newtask, MACH_PORT_RIGHT_DEAD_NAME, portnames[i]))
LOSE;
}
else
{
/* Skip the name we use for any of our own thread ports. */
mach_msg_type_number_t j;
for (j = 0; j < nthreads; ++j)
if (portnames[i] == threads[j])
break;
if (j < nthreads)
continue;
/* Copy our own send right. */
insert = portnames[i];
}
/* Find out how many user references we have for
the send right with this name. */
if (err = __mach_port_get_refs (__mach_task_self (),
portnames[i],
MACH_PORT_RIGHT_SEND,
record_refs ?: &refs))
LOSE;
if (insert == MACH_PORT_NULL)
continue;
if (insert == portnames[i]
&& (porttypes[i] & MACH_PORT_TYPE_DEAD_NAME))
/* This is a dead name; allocate another dead name
with the same name in the child. */
allocate_dead_name:
err = __mach_port_allocate_name (newtask,
MACH_PORT_RIGHT_DEAD_NAME,
portnames[i]);
else
/* Insert the chosen send right into the child. */
err = __mach_port_insert_right (newtask,
portnames[i],
insert, insert_type);
switch (err)
{
case KERN_NAME_EXISTS:
{
/* It already has a send right under this name (?!).
Well, it starts out with a send right for its task
port, and inherits the bootstrap and exception ports
from us. */
mach_port_t childport;
mach_msg_type_name_t poly;
assert (__mach_port_extract_right (newtask, portnames[i],
MACH_MSG_TYPE_COPY_SEND,
&childport,
&poly) == 0
&& childport == insert
&& __mach_port_deallocate (__mach_task_self (),
childport) == 0);
break;
}
case KERN_INVALID_CAPABILITY:
/* The port just died. It was a send right,
and now it's a dead name. */
goto allocate_dead_name;
default:
LOSE;
break;
case KERN_SUCCESS:
/* Give the child as many user references as we have. */
if (refs > 1
&& (err = __mach_port_mod_refs (newtask,
portnames[i],
MACH_PORT_RIGHT_SEND,
refs - 1)))
LOSE;
}
}
}
/* Unlock the standard port cells. The child must unlock its own
copies too. */
for (i = 0; i < _hurd_nports; ++i)
__spin_unlock (&_hurd_ports[i].lock);
ports_locked = 0;
/* All state has now been copied from the parent. It is safe to
resume other parent threads. */
resume_threads ();
/* Create the child main user thread and signal thread. */
if ((err = __thread_create (newtask, &thread))
|| (err = __thread_create (newtask, &sigthread)))
LOSE;
/* Insert send rights for those threads. We previously allocated
dead name rights with the names we want to give the thread ports
in the child as placeholders. Now deallocate them so we can use
the names. */
if ((err = __mach_port_deallocate (newtask, ss->thread))
|| (err = __mach_port_insert_right (newtask, ss->thread,
thread,
MACH_MSG_TYPE_COPY_SEND)))
LOSE;
/* XXX consumed? (_hurd_sigthread is no more) */
if (thread_refs > 1
&& (err = __mach_port_mod_refs (newtask, ss->thread,
MACH_PORT_RIGHT_SEND,
thread_refs - 1)))
LOSE;
if ((_hurd_msgport_thread != MACH_PORT_NULL) /* Let user have none. */
&& ((err = __mach_port_deallocate (newtask, _hurd_msgport_thread))
|| (err = __mach_port_insert_right (newtask,
_hurd_msgport_thread,
sigthread,
MACH_MSG_TYPE_COPY_SEND))))
LOSE;
if (sigthread_refs > 1
&& (err = __mach_port_mod_refs (newtask, _hurd_msgport_thread,
MACH_PORT_RIGHT_SEND,
sigthread_refs - 1)))
LOSE;
/* This seems like a convenient juncture to copy the proc server's
idea of what addresses our argv and envp are found at from the
parent into the child. Since we happen to know that the child
shares our memory image, it is we who should do this copying. */
{
vm_address_t argv, envp;
err = (__USEPORT (PROC, __proc_get_arg_locations (port, &argv, &envp))
?: __proc_set_arg_locations (newproc, argv, envp));
if (err)
LOSE;
}
/* Set the child signal thread up to run the msgport server function
using the same signal thread stack copied from our address space.
We fetch the state before longjmp'ing it so that miscellaneous
registers not affected by longjmp (such as i386 segment registers)
are in their normal default state. */
statecount = MACHINE_THREAD_STATE_COUNT;
if (err = __thread_get_state (_hurd_msgport_thread,
MACHINE_THREAD_STATE_FLAVOR,
(natural_t *) &state, &statecount))
LOSE;
#ifdef STACK_GROWTH_UP
if (__hurd_sigthread_stack_base == 0)
{
state.SP &= __hurd_threadvar_stack_mask;
state.SP += __hurd_threadvar_stack_offset;
}
else
state.SP = __hurd_sigthread_stack_base;
#else
if (__hurd_sigthread_stack_end == 0)
{
/* The signal thread has a stack assigned by cthreads.
The threadvar_stack variables conveniently tell us how
to get to the highest address in the stack, just below
the per-thread variables. */
state.SP &= __hurd_threadvar_stack_mask;
state.SP += __hurd_threadvar_stack_offset;
}
else
state.SP = __hurd_sigthread_stack_end;
#endif
MACHINE_THREAD_STATE_SET_PC (&state,
(unsigned long int) _hurd_msgport_receive);
/* Do special signal thread setup for TLS if needed. */
if (err = _hurd_tls_fork (sigthread, _hurd_msgport_thread, &state))
LOSE;
if (err = __thread_set_state (sigthread, MACHINE_THREAD_STATE_FLAVOR,
(natural_t *) &state, statecount))
LOSE;
/* We do not thread_resume SIGTHREAD here because the child
fork needs to do more setup before it can take signals. */
/* Set the child user thread up to return 1 from the setjmp above. */
_hurd_longjmp_thread_state (&state, env, 1);
/* Do special thread setup for TLS if needed. */
if (err = _hurd_tls_fork (thread, ss->thread, &state))
LOSE;
if (err = __thread_set_state (thread, MACHINE_THREAD_STATE_FLAVOR,
(natural_t *) &state, statecount))
LOSE;
/* Get the PID of the child from the proc server. We must do this
before calling proc_child below, because at that point any
authorized POSIX.1 process may kill the child task with SIGKILL. */
if (err = __USEPORT (PROC, __proc_task2pid (port, newtask, &pid)))
LOSE;
/* Register the child with the proc server. It is important that
this be that last thing we do before starting the child thread
running. Once proc_child has been done for the task, it appears
as a POSIX.1 process. Any errors we get must be detected before
this point, and the child must have a message port so it responds
to POSIX.1 signals. */
if (err = __USEPORT (PROC, __proc_child (port, newtask)))
LOSE;
/* This must be the absolutely last thing we do; we can't assume that
the child will remain alive for even a moment once we do this. We
ignore errors because we have committed to the fork and are not
allowed to return them after the process becomes visible to
POSIX.1 (which happened right above when we called proc_child). */
(void) __thread_resume (thread);
lose:
if (ports_locked)
for (i = 0; i < _hurd_nports; ++i)
__spin_unlock (&_hurd_ports[i].lock);
resume_threads ();
if (newtask != MACH_PORT_NULL)
{
if (err)
__task_terminate (newtask);
__mach_port_deallocate (__mach_task_self (), newtask);
}
if (thread != MACH_PORT_NULL)
__mach_port_deallocate (__mach_task_self (), thread);
if (sigthread != MACH_PORT_NULL)
__mach_port_deallocate (__mach_task_self (), sigthread);
if (newproc != MACH_PORT_NULL)
__mach_port_deallocate (__mach_task_self (), newproc);
if (portnames)
__vm_deallocate (__mach_task_self (),
(vm_address_t) portnames,
nportnames * sizeof (*portnames));
if (porttypes)
__vm_deallocate (__mach_task_self (),
(vm_address_t) porttypes,
nporttypes * sizeof (*porttypes));
if (threads)
{
for (i = 0; i < nthreads; ++i)
__mach_port_deallocate (__mach_task_self (), threads[i]);
__vm_deallocate (__mach_task_self (),
(vm_address_t) threads,
nthreads * sizeof (*threads));
}
/* Release malloc locks. */
_hurd_malloc_fork_parent ();
call_function_static_weak (__malloc_fork_unlock_parent);
/* Run things that want to run in the parent to restore it to
normality. Usually prepare hooks and parent hooks are
symmetrical: the prepare hook arrests state in some way for the
fork, and the parent hook restores the state for the parent to
continue executing normally. */
RUN_HOOK (_hurd_fork_parent_hook, ());
}
else
{
struct hurd_sigstate *oldstates;
/* We are the child task. Unlock the standard port cells, which were
locked in the parent when we copied its memory. The parent has
inserted send rights with the names that were in the cells then. */
for (i = 0; i < _hurd_nports; ++i)
__spin_unlock (&_hurd_ports[i].lock);
/* Claim our sigstate structure and unchain the rest: the
threads existed in the parent task but don't exist in this
task (the child process). Delay freeing them until later
because some of the further setup and unlocking might be
required for free to work. Before we finish cleaning up,
we will reclaim the signal thread's sigstate structure (if
it had one). */
oldstates = _hurd_sigstates;
if (oldstates == ss)
oldstates = ss->next;
else
{
while (_hurd_sigstates->next != ss)
_hurd_sigstates = _hurd_sigstates->next;
_hurd_sigstates->next = ss->next;
}
ss->next = NULL;
_hurd_sigstates = ss;
__mutex_unlock (&_hurd_siglock);
/* Earlier on, the global sigstate may have been tainted and now needs to
be reinitialized. Nobody is interested in its present state anymore:
we're not, the signal thread will be restarted, and there are no other
threads.
We can't simply allocate a fresh global sigstate here, as
_hurd_thread_sigstate will call malloc and that will deadlock trying
to determine the current thread's sigstate. */
#if 0
_hurd_thread_sigstate_init (_hurd_global_sigstate, MACH_PORT_NULL);
#else
/* Only reinitialize the lock -- otherwise we might have to do additional
setup as done in hurdsig.c:_hurdsig_init. */
__spin_lock_init (&_hurd_global_sigstate->lock);
#endif
/* We are one of the (exactly) two threads in this new task, we
will take the task-global signals. */
_hurd_sigstate_set_global_rcv (ss);
/* Fetch our new process IDs from the proc server. No need to
refetch our pgrp; it is always inherited from the parent (so
_hurd_pgrp is already correct), and the proc server will send us a
proc_newids notification when it changes. */
err = __USEPORT (PROC, __proc_getpids (port, &_hurd_pid, &_hurd_ppid,
&_hurd_orphaned));
/* Forking clears the trace flag and pending masks. */
__sigemptyset (&_hurdsig_traced);
__sigemptyset (&_hurd_global_sigstate->pending);
__sigemptyset (&ss->pending);
/* Release malloc locks. */
_hurd_malloc_fork_child ();
call_function_static_weak (__malloc_fork_unlock_child);
/* Run things that want to run in the child task to set up. */
RUN_HOOK (_hurd_fork_child_hook, ());
/* Set up proc server-assisted fault recovery for the signal thread. */
_hurdsig_fault_init ();
/* Start the signal thread listening on the message port. */
if (!err)
err = __thread_resume (_hurd_msgport_thread);
/* Reclaim the signal thread's sigstate structure and free the
other old sigstate structures. */
while (oldstates != NULL)
{
struct hurd_sigstate *next = oldstates->next;
if (oldstates->thread == _hurd_msgport_thread)
{
/* If we have a second signal state structure then we
must have been through here before--not good. */
assert (_hurd_sigstates->next == 0);
_hurd_sigstates->next = oldstates;
oldstates->next = 0;
}
else
free (oldstates);
oldstates = next;
}
/* XXX what to do if we have any errors here? */
pid = 0;
}
/* Unlock things we locked before creating the child task.
They are locked in both the parent and child tasks. */
{
void *const *p;
for (p = symbol_set_first_element (_hurd_fork_locks);
! symbol_set_end_p (_hurd_fork_locks, p);
++p)
__mutex_unlock (*p);
}
_hurd_critical_section_unlock (ss);
if (!err)
{
if (pid != 0)
RUN_HOOK (_hurd_atfork_parent_hook, ());
else
RUN_HOOK (_hurd_atfork_child_hook, ());
}
return err ? __hurd_fail (err) : pid;
}
libc_hidden_def (__fork)
weak_alias (__fork, fork)
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