Date: Sun, 13 Aug 2006 18:41:59 -0700
From: Andrew Morton <akpm@osdl.org>
To: Voluspa <lista1@comhem.se>
Cc: arjan@linux.intel.com, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] lockdep: disable lock debugging when kernel state
 becomes untrusted
Message-Id: <20060813184159.b536736f.akpm@osdl.org>
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On Mon, 14 Aug 2006 03:09:54 +0200
Voluspa <lista1@comhem.se> wrote:

> On 2006-07-10 21:02:59 git-commits-head received:
> > commit 2c16e9c888985761511bd1905b00fb271169c3c0
> > tree e17756b3ed27b0f4953547c39cf46864cdd6f818
> > parent e54695a59c278b9ff48cd4b263da7a1d392f5061
> > author Arjan van de Ven Mon, 10 Jul 2006
> > 18:45:42 -0700 committer Linus Torvalds Tue, 11
> > Jul 2006 03:24:27 -0700
> >
> > [PATCH] lockdep: disable lock debugging when kernel state becomes
> > untrusted
> >
> > Disable lockdep debugging in two situations where the integrity of the
> > kernel no longer is guaranteed: when oopsing and when hitting a
> > tainting-condition.  The goal is to not get weird lockdep traces that
> > don't make sense or are otherwise undebuggable, to not waste time.
> >
> > Lockdep assumes that the previous state it knows about is valid to
> > operate, which is why lockdep turns itself off after the first
> > violation it reports, after that point it can no longer make that
> > assumption.
> >
> > A kernel oops means that the integrity of the kernel compromised; in
> > addition anything lockdep would report is of lesser importance than the
> > oops.
> >
> > All the tainting conditions are of similar integrity-violating nature
> > and also make debugging/diagnosing more difficult.
> 
> On my x86_64 notebook I need ndiswrapper. No but-s, if-s or anything-s.
> Period. I also have to work outside of X in a clean terminal (console).
> 
> This patch unfortunately creates a 'pipe' directly from
>  /var/log/messages to the screen. So if I work in a textbased program,
> and something happens in the log, the program gets a broken interface.
> Programs that simultaniously output to the log becomes unusable.
> 
> It is also darn irritating when text strings materializes at the shell
> prompt...
> 
> Once the 'pipe' is established (by tainting) it can not be reverted by
> eg rmmod ndiswrapper.
> 
> I haven't even enabled any lockdep debugging:

That would appear to be a bug.  debug_locks_off() is running
console_verbose() waaaay after the locking selftest code has completed.

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