linux-kernel - [PATCH 03/12] tty: note race we need to fix

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Message-ID: <20120622153900.1405.47389.stgit@localhost.localdomain>
Date:	Fri, 22 Jun 2012 16:40:20 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	greg@...ah.com, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: [PATCH 03/12] tty: note race we need to fix

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 <alan@...ux.intel.com>
---

 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)

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