Subject: Re: linux-next: PowerPC WARN_ON_ONCE() after merge of the final tree (tip related)

From: Ingo Molnar <[email-masked]>
Date: Thu, 15 Apr 2010 09:32:56 +0200

* David Miller <[email-masked]> wrote:

> From: Ingo Molnar <[email-masked]>
> Date: Thu, 15 Apr 2010 08:49:40 +0200
> 
> > Btw., WARN_ON trapping on PowerPC is clearly a PowerPC bug - there's a good 
> > reason we have WARN_ON versus BUG_ON - it should be fixed.
> 
> I disagree, an implementation should be allowed to use the most
> efficient implementation possible for both interfaces.

It trades robustness for slightly better space/code efficiency.

Such a trap based mechanism exists on x86 as well and we use it for BUG_ON(). 
We intentionally dont use it to generate warnings and dont override __WARN(), 
because it would blow up way too often when a warning triggers in some 
sensitive codepath that cannot take a trap.

Anyway, the warning obviously has to be fixed - but the boot crash itself is 
PowerPC's own doing.

	Ingo