Message-ID: <555B5100.8010708@kynesim.co.uk>
Date: Tue, 19 May 2015 16:04:32 +0100
From: Richard Watts <rrw@kynesim.co.uk>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0
MIME-Version: 1.0
To: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org
Subject: [PATCH 0/1] Avoid usb reset crashes by making tty_io cdevs truly
 dynamic
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1339
Lines: 32

Sometimes, usb buses on which CDC ACM devices sit encounter a usb reset.

When this happens, particularly when CONFIG_DEBUG_KOBJECT_RELEASE is on,
we attempt to destroy the cdev for the associated tty and then
rapidly re-initialise it. Since kobject destruction is not immediate,
this potentially leaves us with cdev_init() calling kobject_init() on a
kobject that is about to be destroyed.

This turns out not to be such a good thing and this patch solves the
problem by making the cdevs tty_operations->cdevs dynamically
allocated.

This may not be a problem in the wild (though I have some circumstantial
evidence that it is), but I submit that we might want to think about
fixing it anyway, since it makes debugging on systems with
CONFIG_DEBUG_KOBJECT_RELEASE=y and USB resets rather difficult
(guess what I have been doing lately .. ).

Patch is against e26081808edadfd257c6c9d81014e3b25e9a6118 (head of
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git ).

  (in fact, you will still get an oops - which is the subject of
another, more controversial, patchset ..)


Richard.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/