linux-kernel - Re: kernel: sysctl table check failed: /dev/parport/parport0/devices/ppdev0/timeslice Sysctl already exists

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Message-ID: <m1wslb1wpb.fsf@frodo.ebiederm.org>
Date:	Fri, 30 May 2008 11:19:28 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Dave Jones <davej@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: kernel: sysctl table check failed: /dev/parport/parport0/devices/ppdev0/timeslice Sysctl already exists

Dave Jones <davej@...hat.com> writes:

> Well, that's umm, special.
> I wonder if powering off the printer isn't causing the sysctl to be removed,
> causing the next power-on to look like a new device ?
> Eric, you poked around the sysctl paths in parport last year, any ideas?

Yes.  The short answer is that this is a real bug in the parport code
that has existed forever.  We just now complain.

http://bugzilla.kernel.org/show_bug.cgi?id=9749

It takes something like two accessors of the parallel port to trigger
this.  Though not in a bad way.

In particular each open creates the sysctl for the duration of the
open (or something like that) and so if you open (I think it is
/dev/parport0) twice you try and create the sysctls twice.

I got as far as basic confirmation of this bug, and a rough cause of
it.  Unfortunately I have not had the time to unscramble it, and neither
it seems has anyone else.

Eric
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