Message-ID: <47F01FF4.2010307@linux.intel.com>
Date: Sun, 30 Mar 2008 16:19:16 -0700
From: Arjan van de Ven <arjan@linux.intel.com>
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To: =?ISO-8859-1?Q?Bj=F6rn_Steinbrink?= <B.Steinbrink@gmx.de>
CC: Greg KH <greg@kroah.com>, Linus Torvalds <torvalds@linux-foundation.org>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Johannes Berg <johannes@sipsolutions.net>,
       Jiri Kosina <jkosina@suse.cz>
Subject: Re: [PATCH] evdev: Release eventual input device grabs when	getting
 disconnected
References: <20080330184259.GB21375@atjola.homenet> <alpine.LFD.1.00.0803301448190.14670@woody.linux-foundation.org> <20080330222228.GA2419@kroah.com> <20080330224203.GA22498@atjola.homenet>
In-Reply-To: <20080330224203.GA22498@atjola.homenet>
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Bj?rn 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@johannes.berg>
> 

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