tty: fix logic change introduced by wait_event_interruptible_timeout()

Commit 5a52bd4a2dcb570333ce6fe2e16cd311650dbdc8 introduced a subtle logic
change in tty_wait_until_sent().  The original version would only error out
of the 'do { ...  } while (timeout)' loop if signal_pending() evaluated to
true; a timeout or break due to an empty buffer would fall out of the loop
and into the tty->driver->wait_until_sent handling.  The current
implementation will error out on either a pending signal or an empty
buffer, falling through to the tty->driver->wait_until_sent handling only
on a timeout.

The ->wait_until_sent() will not be reached if the buffer empties before
timeout jiffies have elapsed.  This behavior differs from that prior to commit
5a52bd4a2dcb570333ce6fe2e16cd311650dbdc8.

I turned this up while using a little serial download utility to bootstrap an
ARM-based eval board.  The util worked fine on 2.6.22.x, but consistently
failed on 2.6.23.x.  Once I'd determined that, I narrowed things down with git
bisect, and found the above difference in logic in tty_wait_until_sent() by
inspection.

This change reverts the logic flow in tty_wait_until_sent() to match that
prior to the aforementioned commit.

Signed-off-by: Cory T. Tusar <[email protected]>
Cc: Alan Cox <[email protected]>
Acked-by: Jiri Slaby <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index 1bdd2bf4f37d..e02d59245a17 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -62,7 +62,7 @@ void tty_wait_until_sent(struct tty_struct * tty, long timeout)
 	if (!timeout)
 		timeout = MAX_SCHEDULE_TIMEOUT;
 	if (wait_event_interruptible_timeout(tty->write_wait,
-			!tty->driver->chars_in_buffer(tty), timeout))
+			!tty->driver->chars_in_buffer(tty), timeout) < 0)
 		return;
 	if (tty->driver->wait_until_sent)
 		tty->driver->wait_until_sent(tty, timeout);