From 36614259f65555c6194d8d5dcd554a1ded0458a5 Mon Sep 17 00:00:00 2001
From: Johan Hovold <jhovold@gmail.com>
Date: Wed, 13 Feb 2013 17:53:28 +0100
Subject: [PATCH] USB: serial: fix null-pointer dereferences on disconnect

commit b2ca699076573c94fee9a73cb0d8645383b602a0 upstream.

Make sure serial-driver dtr_rts is called with disc_mutex held after
checking the disconnected flag.

Due to a bug in the tty layer, dtr_rts may get called after a device has
been disconnected and the tty-device unregistered. Some drivers have had
individual checks for disconnect to make sure the disconnected interface
was not accessed, but this should really be handled in usb-serial core
(at least until the long-standing tty-bug has been fixed).

Note that the problem has been made more acute with commit 0998d0631001
("device-core: Ensure drvdata = NULL when no driver is bound") as the
port data is now also NULL when dtr_rts is called resulting in further
oopses.

Reported-by: Chris Ruehl <chris.ruehl@gtsys.com.hk>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - Adjust context
 - Drop changes to quatech2.c]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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