linux-kernel - Re: Oops in evdev_disconnect for kernel 2.6.23.12

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Message-ID: <478033ED.7050907@nigel.suspend2.net>
Date:	Sun, 06 Jan 2008 12:50:37 +1100
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Berthold Cogel <cogel@...-koeln.de>
CC:	Al Viro <viro@...IV.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: Oops in evdev_disconnect for kernel 2.6.23.12

Hi.

Berthold Cogel wrote:
> Al Viro schrieb:
>> On Tue, Jan 01, 2008 at 08:26:05PM +0100, Berthold Cogel wrote:
>>
>>> Jan  1 17:34:39 wonderland kernel: BUG: unable to handle kernel
>>> paging request at virtual address 00100100
>>
>> LIST_POISON1
>>
>>> Jan  1 17:34:39 wonderland kernel: EIP is at evdev_disconnect+0x65/0x9e 
>>
>> and by the look of code, it's a bit before the call of something that
>> gets
>> 0x20006 as one of its arguments.  Which, by the look of evdev.s, gets
>> passed only to kill_fasync().  So it's POLL_HUP, so this code could be
>> these days:
>>     spin_lock(&evdev->client_lock);
>>     list_for_each_entry(client, &evdev->client_list, node)
>>         kill_fasync(&client->fasync, SIGIO, POLL_HUP);
>>     spin_unlock(&evdev->client_lock);
>> in evdev_hangup()
>> prior to commit 6addb1d6de1968b84852f54561cc9a999909b5a9:
>>         list_for_each_entry(client, &evdev->client_list, node)
>>             kill_fasync(&client->fasync, SIGIO, POLL_HUP);
>> in evdev_disconnect()
>>
>>
>>> I'm using Debian stable/testing/unstable with homemade kernel
>>> 2.6.23.12 (patched with tuxonice-3.0-rc3-for-2.6.23.9).
>>
>> ... and seeing that this changeset postdates 2.6.23 *and* adds locking to
>> the lists we are traversing in either variant, I'd bet that the kernel
>> you
>> have does *NOT* have the changeset in question, that you have list
>> corruption
>> from race and that your oops is list_for_each_entry() trying to walk
>> forward from entry that just had list_del() poisoning its ->next.
>>
>> There are only 4 changesets between 2.6.23 and this one affecting
>> drivers/input
>> and only
>> 8006479c9b75fb6594a7b746af3d7f1fbb68f18f and
>> 6addb1d6de1968b84852f54561cc9a999909b5a9
>> appear to be relevant.  Apply to your kernel and see if it helps...
> 
> Looks as if I have to start using git ... I always feared that this day
> will come. ;-)
> 
> If I'm able to reproduce the oops with my patched kernel, I will gladly
> follow your advice.
> 
> Regards,
> 
> Berthold

I can't do it immediately but I'll send you the patches to try a later
in the day if you like.

Nigel
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