pty: Fix buffer flush deadlock
The pty driver does not clear its write buffer when commanded.
This is to avoid an apparent deadlock between parallel flushes from
both pty ends; specifically when handling either BRK or INTR input.
However, parallel flushes from this source is not possible since
the pty master can never be set to BRKINT or ISIG. Parallel flushes
from other sources are possible but these do not threaten deadlocks.
Annotate the tty buffer mutex for lockdep to represent the nested
tty_buffer locking which occurs when the pty slave is processing input
(its buffer mutex held) and receives INTR or BRK and acquires the
linked tty buffer mutex via tty_buffer_flush().
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index f882ac8..0e27315 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -212,10 +212,16 @@
static void pty_flush_buffer(struct tty_struct *tty)
{
struct tty_struct *to = tty->link;
+ struct tty_ldisc *ld;
if (!to)
return;
- /* tty_buffer_flush(to); FIXME */
+
+ ld = tty_ldisc_ref(to);
+ tty_buffer_flush(to, ld);
+ if (ld)
+ tty_ldisc_deref(ld);
+
if (to->packet) {
spin_lock_irq(&tty->ctrl_lock);
tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
@@ -425,6 +431,8 @@
tty->port = ports[1];
o_tty->port->itty = o_tty;
+ tty_buffer_set_lock_subclass(o_tty->port);
+
tty_driver_kref_get(driver);
tty->count++;
o_tty->count++;
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 3605103..7566164 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -557,3 +557,9 @@
return 0;
}
EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
+
+/* slave ptys can claim nested buffer lock when handling BRK and INTR */
+void tty_buffer_set_lock_subclass(struct tty_port *port)
+{
+ lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
+}