linux-kernel - Re: [PATCH] evdev: Release eventual input device grabs when getting disconnected

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Date:	Sun, 30 Mar 2008 16:19:16 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Björn Steinbrink <B.Steinbrink@....de>
CC:	Greg KH <greg@...ah.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Johannes Berg <johannes@...solutions.net>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH] evdev: Release eventual input device grabs when	getting
 disconnected

Björn Steinbrink wrote:
> On 2008.03.30 15:22:28 -0700, Greg KH wrote:
>> On Sun, Mar 30, 2008 at 02:51:02PM -0700, Linus Torvalds wrote:
>>> On Sun, 30 Mar 2008, Bj?rn Steinbrink wrote:
>>>> I can't reproduce the bug on my UP box and currently can't afford
>>>> crashing my SMP box (all the oopses seem to come from SMP kernels, so I
>>>> guess it needs SMP to crash), so while this doesn't show any new
>>>> problems, I can't tell whether it actually fixes anything. Testers
>>>> welcome!
>>> Ok, I applied this because I will do an -rc8 today or tomorrow, but I 
>>> really really hope somebody can figure out what made this all start to 
>>> trigger. It does smell like some core device layer change, because we do 
>>> not seem to have a lot of changes since 2.6.24 in evdev.c and input.c that 
>>> seem relevant.
>>>
>>> Greg, are there any refcounting changes that would cause the input devices 
>>> to be free'd earlier or something?
>> Earlier?  No, not that I know of at all, as long as the reference
>> counting logic was correct originally.  All of the problems we have been
>> fixing were ones where we accidentally were grabbing too many references
>> and then wondering why things were not getting cleaned up properly as
>> the kobject rework exposed these problems making them more obvious.
> 
> Not freeing the input device at all would of course also hide any
> access-after-free problems :-) So if that's the case, that might explain
> the sudden exposure of the problem. IMHO, my patch is the right thing to
> do anyway, because releasing a grab on the underlying input device from
> within evdev clearly needs to happen before we release that device. So
> AFAICT we're really just looking for "why do we see that bug now?" and
> "is there another bug?"
> 
>> I haven't heard of the opposite happening.  Anything that I can try to
>> test for here, I have a lot of removable input devices to test with.
> 
> Sorry, forgot to set the In-Reply-To header when sending the patch. The
> original thread, with a reproducing recipe is here:
> http://lkml.org/lkml/2008/3/28/442
> Message-Id: <1206742499.22530.90.camel@...annes.berg>
> 

one note.. you do want to enable slab poison, just to catch the bug right away...
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