tty: Prepare for destroying line discipline on hangup
tty file_operations (read/write/ioctl) wait for the ldisc reference
indefinitely (until ldisc lifetime events, such as hangup or TIOCSETD,
finish). Since hangup now destroys the ldisc and does not instance
another copy, file_operations must now be prepared to receive a NULL
ldisc reference from tty_ldisc_ref_wait():
CPU 0 CPU 1
----- -----
(*f_op->read)() => tty_read()
__tty_hangup()
...
f_op = &hung_up_tty_fops;
...
tty_ldisc_hangup()
tty_ldisc_lock()
tty_ldisc_kill()
tty->ldisc = NULL
tty_ldisc_unlock()
ld = tty_ldisc_ref_wait()
/* ld == NULL */
Instead, the action taken now is to return the same value as if the
tty had been hungup a moment earlier:
CPU 0 CPU 1
----- -----
__tty_hangup()
...
f_op = &hung_up_tty_fops;
(*f_op->read)() => hung_up_tty_read()
return 0;
...
tty_ldisc_hangup()
tty_ldisc_lock()
tty_ldisc_kill()
tty->ldisc = NULL
tty_ldisc_unlock()
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 71a9409..eb26754 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1068,6 +1068,8 @@
/* We want to wait for the line discipline to sort out in this
situation */
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return hung_up_tty_read(file, buf, count, ppos);
if (ld->ops->read)
i = ld->ops->read(tty, file, buf, count);
else
@@ -1242,6 +1244,8 @@
if (tty->ops->write_room == NULL)
tty_err(tty, "missing write_room method\n");
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return hung_up_tty_write(file, buf, count, ppos);
if (!ld->ops->write)
ret = -EIO;
else
@@ -2201,6 +2205,8 @@
return 0;
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return hung_up_tty_poll(filp, wait);
if (ld->ops->poll)
ret = ld->ops->poll(tty, filp, wait);
tty_ldisc_deref(ld);
@@ -2290,6 +2296,8 @@
return -EFAULT;
tty_audit_tiocsti(tty, ch);
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return -EIO;
ld->ops->receive_buf(tty, &ch, &mbz, 1);
tty_ldisc_deref(ld);
return 0;
@@ -2682,6 +2690,8 @@
int ret;
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return -EIO;
ret = put_user(ld->ops->num, p);
tty_ldisc_deref(ld);
return ret;
@@ -2979,6 +2989,8 @@
return retval;
}
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return hung_up_tty_ioctl(file, cmd, arg);
retval = -EINVAL;
if (ld->ops->ioctl) {
retval = ld->ops->ioctl(tty, file, cmd, arg);
@@ -3007,6 +3019,8 @@
}
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return hung_up_tty_compat_ioctl(file, cmd, arg);
if (ld->ops->compat_ioctl)
retval = ld->ops->compat_ioctl(tty, file, cmd, arg);
else