From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: [PATCH 03/12] tty: note race we need to fix Date: Fri, 22 Jun 2012 16:40:20 +0100 Message-ID: <20120622153900.1405.47389.stgit@localhost.localdomain> References: <20120622153600.1405.15575.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:40738 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762296Ab2FVPYc (ORCPT ); Fri, 22 Jun 2012 11:24:32 -0400 In-Reply-To: <20120622153600.1405.15575.stgit@localhost.localdomain> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: greg@kroah.com, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org This was identified by Vincent Pillet with a high speed interface that uses low latency mode. In the low latency case we have a tiny race but it can be hit. Signed-off-by: Alan Cox --- drivers/tty/n_tty.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index ee1c268..4f34491 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1432,6 +1432,12 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp, */ if (tty->receive_room < TTY_THRESHOLD_THROTTLE) tty_throttle(tty); + + /* FIXME: there is a tiny race here if the receive room check runs + before the other work executes and empties the buffer (upping + the receiving room and unthrottling. We then throttle and get + stuck. This has been observed and traced down by Vincent Pillet/ + We need to address this when we sort out out the rx path locking */ } int is_ignored(int sig)