diff options
| -rw-r--r-- | drivers/char/pty.c | 53 |
1 files changed, 40 insertions, 13 deletions
diff --git a/drivers/char/pty.c b/drivers/char/pty.c index 5acd29e6e04..daebe1ba43d 100644 --- a/drivers/char/pty.c +++ b/drivers/char/pty.c @@ -95,23 +95,34 @@ static void pty_unthrottle(struct tty_struct *tty) * a count. * * FIXME: Our pty_write method is called with our ldisc lock held but - * not our partners. We can't just take the other one blindly without - * risking deadlocks. + * not our partners. We can't just wait on the other one blindly without + * risking deadlocks. At some point when everything has settled down we need + * to look into making pty_write at least able to sleep over an ldisc change. + * + * The return on no ldisc is a bit counter intuitive but the logic works + * like this. During an ldisc change the other end will flush its buffers. We + * thus return the full length which is identical to the case where we had + * proper locking and happened to queue the bytes just before the flush during + * the ldisc change. */ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int count) { struct tty_struct *to = tty->link; - int c; + struct tty_ldisc *ld; + int c = count; if (!to || tty->stopped) return 0; - - c = to->receive_room; - if (c > count) - c = count; - to->ldisc->ops->receive_buf(to, buf, NULL, c); - + ld = tty_ldisc_ref(to); + + if (ld) { + c = to->receive_room; + if (c > count) + c = count; + ld->ops->receive_buf(to, buf, NULL, c); + tty_ldisc_deref(ld); + } return c; } @@ -145,14 +156,23 @@ static int pty_write_room(struct tty_struct *tty) static int pty_chars_in_buffer(struct tty_struct *tty) { struct tty_struct *to = tty->link; - int count; + struct tty_ldisc *ld; + int count = 0; /* We should get the line discipline lock for "tty->link" */ - if (!to || !to->ldisc->ops->chars_in_buffer) + if (!to) + return 0; + /* We cannot take a sleeping reference here without deadlocking with + an ldisc change - but it doesn't really matter */ + ld = tty_ldisc_ref(to); + if (ld == NULL) return 0; /* The ldisc must report 0 if no characters available to be read */ - count = to->ldisc->ops->chars_in_buffer(to); + if (ld->ops->chars_in_buffer) + count = ld->ops->chars_in_buffer(to); + + tty_ldisc_deref(ld); if (tty->driver->subtype == PTY_TYPE_SLAVE) return count; @@ -182,12 +202,19 @@ static void pty_flush_buffer(struct tty_struct *tty) { struct tty_struct *to = tty->link; unsigned long flags; + struct tty_ldisc *ld; if (!to) return; + ld = tty_ldisc_ref(to); + + /* The other end is changing discipline */ + if (!ld) + return; - if (to->ldisc->ops->flush_buffer) + if (ld->ops->flush_buffer) to->ldisc->ops->flush_buffer(to); + tty_ldisc_deref(ld); if (to->packet) { spin_lock_irqsave(&tty->ctrl_lock, flags); |