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

Frederic Weisbecker
2009-04-10T13:35:17Z

On Fri, Apr 10, 2009 at 02:12:43PM +0200, Ingo Molnar wrote:
>
> * 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

Yeah, I first wanted to do so but was shy about the oops_in_progress = 1
inside debug_locks_off(). Isn't it a problem?

Thanks,
Frederic.