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@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index ee1c268f5f9d6582da5b0eeb5121ada945fcd800..4f34491b65c62fd61f6111b35df7a3ce03cf94a6 100644 (file)
--- 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)