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

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Date:	Thu, 15 Apr 2010 09:32:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	sfr@...b.auug.org.au, tglx@...utronix.de, hpa@...or.com,
	peterz@...radead.org, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, fweisbec@...il.com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: linux-next: PowerPC WARN_ON_ONCE() after merge of the final tree
 (tip related)


* David Miller <davem@...emloft.net> wrote:

> From: Ingo Molnar <mingo@...e.hu>
> 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
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