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

Ingo Molnar
2009-04-10T12:13:32Z

* Frederic Weisbecker <fweisbec@gmail.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@gmail.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