Re: [2/3] 2.6.22-rc2: known regressions v2

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> > Looks like this is in DRM code:
> > 
> > BUG: at include/linux/slub_def.h:88 kmalloc_index()
> 
> I'm going to change that "BUG:" to "WARNING:".
> 
> I know some people disagreed with it (ie Ingo), but I think that's 
> total and utter bullshit.
> 
> It's a warning. Right now that "BUG:" message makes people all scared 
> about something that is not fatal at all, just a note that something 
> hasn't been converted, but is expected to work absolutely fine.
> 
> Calling it a bug is idiotic.

i very much agree that this kmalloc_index() one shouldnt be called a 
"BUG: ", but if you look at the majority of WARN_ON() instances they are 
checks for clear, serious kernel bugs. Very often we use WARN_ON() not 
to signal that it's just a harmless warning, but because we do not want 
to bring the system down via a BUG_ON(). The API is misnamed for sure, 
but still, the purpose and current practice is clear: to signal kernel 
bugs.

To quantify this a bit more objectively i just did a "grep WARN_ON 
kernel/*.c" and randomly picked 10 out of the 113 WARN_ON()'s:

 kernel/cpu.c:			WARN_ON(1);
 kernel/exit.c:	WARN_ON(atomic_read(&tsk->fs_excl));
 kernel/fork.c:	WARN_ON(!(tsk->exit_state & (EXIT_DEAD | EXIT_ZOMBIE)));
 kernel/futex.c:	WARN_ON(!pi_state);
 kernel/hrtimer.c:		WARN_ON_ONCE(timer->cb_mode ==  HRTIMER_CB_IRQSAFE_NO_SOFTIRQ);
 kernel/lockdep.c:		WARN_ON(1);
 kernel/mutex-debug.c:	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
 kernel/rtmutex.c:	WARN_ON(rt_mutex_is_locked(lock));
 kernel/sched.c:	if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
 kernel/softirq.c:       WARN_ON_ONCE(in_irq());

and reviewed each instance, each and every one of these warnings is a 
serious kernel bug that i would not 'warn' about, but what i'd like to 
see reported ASAP. [ In fact i added 5 of these WARN_ON()s :-/ ] But 
maybe that's just me?

now regarding the naming of this API, i'd very much agree to do this 
rename:

   WARN_ON  =>  BUG_ON
   BUG_ON   =>  CRASH_ON

and make WARN_ON() print a "WARNING: ".

and i signalled this in the original discussion too a few months ago 
when i opposed the watering-down of the WARN_ON printk.

OTOH i dont feel that strongly about all this :-)

	Ingo