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/vt/selection.c b/drivers/tty/vt/selection.c
index 381a2b1..4dd9dd2 100644
--- a/drivers/tty/vt/selection.c
+++ b/drivers/tty/vt/selection.c
@@ -347,6 +347,8 @@
console_unlock();
ld = tty_ldisc_ref_wait(tty);
+ if (!ld)
+ return -EIO; /* ldisc was hung up */
tty_buffer_lock_exclusive(&vc->port);
add_wait_queue(&vc->paste_wait, &wait);