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

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Message-ID: <47801D70.8020504@uni-koeln.de>
Date:	Sun, 06 Jan 2008 01:14:40 +0100
From:	Berthold Cogel <cogel@...-koeln.de>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Oops in evdev_disconnect for kernel 2.6.23.12

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


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