kernel-ark/arch/um/os-Linux/sigio.c
Jeff Dike 5f4e8fd08f [PATCH] uml: fix thread startup race
This fixes a race in the starting of write_sigio_thread.  Previously, some of
the data needed by the thread was initialized after the clone.  If the thread
ran immediately, it would see the uninitialized data, including an empty
pollfds, which would cause it to hang.

We move the data initialization to before the clone, and adjust the error
paths and cleanup accordingly.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-27 08:44:38 -08:00

324 lines
6.7 KiB
C

/*
* Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
* Licensed under the GPL
*/
#include <unistd.h>
#include <stdlib.h>
#include <termios.h>
#include <pty.h>
#include <signal.h>
#include <errno.h>
#include <string.h>
#include <sched.h>
#include <sys/socket.h>
#include <sys/poll.h>
#include "init.h"
#include "user.h"
#include "kern_util.h"
#include "user_util.h"
#include "sigio.h"
#include "os.h"
/* Protected by sigio_lock(), also used by sigio_cleanup, which is an
* exitcall.
*/
static int write_sigio_pid = -1;
/* These arrays are initialized before the sigio thread is started, and
* the descriptors closed after it is killed. So, it can't see them change.
* On the UML side, they are changed under the sigio_lock.
*/
#define SIGIO_FDS_INIT {-1, -1}
static int write_sigio_fds[2] = SIGIO_FDS_INIT;
static int sigio_private[2] = SIGIO_FDS_INIT;
struct pollfds {
struct pollfd *poll;
int size;
int used;
};
/* Protected by sigio_lock(). Used by the sigio thread, but the UML thread
* synchronizes with it.
*/
struct pollfds current_poll = {
.poll = NULL,
.size = 0,
.used = 0
};
struct pollfds next_poll = {
.poll = NULL,
.size = 0,
.used = 0
};
static int write_sigio_thread(void *unused)
{
struct pollfds *fds, tmp;
struct pollfd *p;
int i, n, respond_fd;
char c;
signal(SIGWINCH, SIG_IGN);
fds = &current_poll;
while(1){
n = poll(fds->poll, fds->used, -1);
if(n < 0){
if(errno == EINTR) continue;
printk("write_sigio_thread : poll returned %d, "
"errno = %d\n", n, errno);
}
for(i = 0; i < fds->used; i++){
p = &fds->poll[i];
if(p->revents == 0) continue;
if(p->fd == sigio_private[1]){
n = os_read_file(sigio_private[1], &c, sizeof(c));
if(n != sizeof(c))
printk("write_sigio_thread : "
"read failed, err = %d\n", -n);
tmp = current_poll;
current_poll = next_poll;
next_poll = tmp;
respond_fd = sigio_private[1];
}
else {
respond_fd = write_sigio_fds[1];
fds->used--;
memmove(&fds->poll[i], &fds->poll[i + 1],
(fds->used - i) * sizeof(*fds->poll));
}
n = os_write_file(respond_fd, &c, sizeof(c));
if(n != sizeof(c))
printk("write_sigio_thread : write failed, "
"err = %d\n", -n);
}
}
return 0;
}
static int need_poll(int n)
{
if(n <= next_poll.size){
next_poll.used = n;
return(0);
}
kfree(next_poll.poll);
next_poll.poll = um_kmalloc_atomic(n * sizeof(struct pollfd));
if(next_poll.poll == NULL){
printk("need_poll : failed to allocate new pollfds\n");
next_poll.size = 0;
next_poll.used = 0;
return(-1);
}
next_poll.size = n;
next_poll.used = n;
return(0);
}
/* Must be called with sigio_lock held, because it's needed by the marked
* critical section. */
static void update_thread(void)
{
unsigned long flags;
int n;
char c;
flags = set_signals(0);
n = os_write_file(sigio_private[0], &c, sizeof(c));
if(n != sizeof(c)){
printk("update_thread : write failed, err = %d\n", -n);
goto fail;
}
n = os_read_file(sigio_private[0], &c, sizeof(c));
if(n != sizeof(c)){
printk("update_thread : read failed, err = %d\n", -n);
goto fail;
}
set_signals(flags);
return;
fail:
/* Critical section start */
if(write_sigio_pid != -1)
os_kill_process(write_sigio_pid, 1);
write_sigio_pid = -1;
close(sigio_private[0]);
close(sigio_private[1]);
close(write_sigio_fds[0]);
close(write_sigio_fds[1]);
/* Critical section end */
set_signals(flags);
}
int add_sigio_fd(int fd, int read)
{
int err = 0, i, n, events;
sigio_lock();
for(i = 0; i < current_poll.used; i++){
if(current_poll.poll[i].fd == fd)
goto out;
}
n = current_poll.used + 1;
err = need_poll(n);
if(err)
goto out;
for(i = 0; i < current_poll.used; i++)
next_poll.poll[i] = current_poll.poll[i];
if(read) events = POLLIN;
else events = POLLOUT;
next_poll.poll[n - 1] = ((struct pollfd) { .fd = fd,
.events = events,
.revents = 0 });
update_thread();
out:
sigio_unlock();
return(err);
}
int ignore_sigio_fd(int fd)
{
struct pollfd *p;
int err = 0, i, n = 0;
sigio_lock();
for(i = 0; i < current_poll.used; i++){
if(current_poll.poll[i].fd == fd) break;
}
if(i == current_poll.used)
goto out;
err = need_poll(current_poll.used - 1);
if(err)
goto out;
for(i = 0; i < current_poll.used; i++){
p = &current_poll.poll[i];
if(p->fd != fd) next_poll.poll[n++] = current_poll.poll[i];
}
if(n == i){
printk("ignore_sigio_fd : fd %d not found\n", fd);
err = -1;
goto out;
}
update_thread();
out:
sigio_unlock();
return(err);
}
static struct pollfd *setup_initial_poll(int fd)
{
struct pollfd *p;
p = um_kmalloc(sizeof(struct pollfd));
if (p == NULL) {
printk("setup_initial_poll : failed to allocate poll\n");
return NULL;
}
*p = ((struct pollfd) { .fd = fd,
.events = POLLIN,
.revents = 0 });
return p;
}
void write_sigio_workaround(void)
{
unsigned long stack;
struct pollfd *p;
int err;
int l_write_sigio_fds[2];
int l_sigio_private[2];
int l_write_sigio_pid;
/* We call this *tons* of times - and most ones we must just fail. */
sigio_lock();
l_write_sigio_pid = write_sigio_pid;
sigio_unlock();
if (l_write_sigio_pid != -1)
return;
err = os_pipe(l_write_sigio_fds, 1, 1);
if(err < 0){
printk("write_sigio_workaround - os_pipe 1 failed, "
"err = %d\n", -err);
return;
}
err = os_pipe(l_sigio_private, 1, 1);
if(err < 0){
printk("write_sigio_workaround - os_pipe 2 failed, "
"err = %d\n", -err);
goto out_close1;
}
p = setup_initial_poll(l_sigio_private[1]);
if(!p)
goto out_close2;
sigio_lock();
/* Did we race? Don't try to optimize this, please, it's not so likely
* to happen, and no more than once at the boot. */
if(write_sigio_pid != -1)
goto out_free;
current_poll = ((struct pollfds) { .poll = p,
.used = 1,
.size = 1 });
if (write_sigio_irq(l_write_sigio_fds[0]))
goto out_clear_poll;
memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
CLONE_FILES | CLONE_VM, &stack, 0);
if (write_sigio_pid < 0)
goto out_clear;
sigio_unlock();
return;
out_clear:
write_sigio_pid = -1;
write_sigio_fds[0] = -1;
write_sigio_fds[1] = -1;
sigio_private[0] = -1;
sigio_private[1] = -1;
out_clear_poll:
current_poll = ((struct pollfds) { .poll = NULL,
.size = 0,
.used = 0 });
out_free:
kfree(p);
sigio_unlock();
out_close2:
close(l_sigio_private[0]);
close(l_sigio_private[1]);
out_close1:
close(l_write_sigio_fds[0]);
close(l_write_sigio_fds[1]);
}
void sigio_cleanup(void)
{
if(write_sigio_pid != -1){
os_kill_process(write_sigio_pid, 1);
write_sigio_pid = -1;
}
}