linux-kernel - Re: [PATCH 1/2] lockdep: warn about lockdep disabling after kernel taint

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Date:	Fri, 10 Apr 2009 14:12:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/2] lockdep: warn about lockdep disabling after kernel
	taint


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> Impact: provide useful missing info for developers
> 
> Kernel taint can occur in several situations such as warnings,
> load of prorietary or staging modules, bad page, etc...
> 
> But when such taint happens, a developer might still be working on
> the kernel, expecting that lockdep is still enabled. But a taint
> disables lockdep without ever warning about it.
> Such a kernel behaviour doesn't really help for kernel development.
> 
> This patch adds this missing warning.
> 
> Since the taint is done most of the time after the main message that
> explain the real source issue, it seems safe to warn about it inside
> add_taint() so that it appears at last, without hurting the main
> information.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> 
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 3fd8c5b..9e7420a 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -213,8 +213,14 @@ unsigned long get_taint(void)
>  
>  void add_taint(unsigned flag)
>  {
> -	/* can't trust the integrity of the kernel anymore: */
> -	debug_locks = 0;
> +	/*
> +	 * Can't trust the integrity of the kernel anymore.
> +	 * We don't call directly debug_locks_off() because the issue
> +	 * is not necessarily serious enough to set oops_in_progress to 1
> +	 */
> +	if (xchg(&debug_locks, 0))
> +		printk(KERN_WARNING "Disabling lockdep due to kernel taint\n");
> +

nice idea - but please use the proper debug_locks_off() construct 
instead of an open-coded xchg(). Something like:

	if (debug_locks_off())
		printk(...);

should do the trick.

	Ingo
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