linux-kernel - Re: Badness on the Warp

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Message-Id: <200906210628.35553.elendil@planet.nl>
Date:	Sun, 21 Jun 2009 06:28:33 +0200
From:	Frans Pop <elendil@...net.nl>
To:	Sean MacLennan <smaclennan@...atech.com>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	David Gibson <david@...son.dropbear.id.au>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: Badness on the Warp

On Sunday 21 June 2009, Sean MacLennan wrote:
> I found the source of the badness. The backtrace is correct:
>
> uic_init_one

So that's in arch/powerpc/sysdev/uic.c.

> ___alloc_bootmem
> ___alloc_bootmem_nopanic
> alloc_arch_preferred_bootmem
>
> In alloc_arch_preferred_bootmem we have:
>
> 	if (WARN_ON_ONCE(slab_is_available()))
> 		return kzalloc(size, GFP_NOWAIT);
>
> Since the slab is available (it had better be or the call will return
> NULL), we get the badness message, then a successful return from
> kzalloc.
>
> I believe the author wants something like:
>
> 	if (slab_is_available())
> 		return kzalloc(size, GFP_NOWAIT);
> 	else
> 		WARN_ON_ONCE(1);

Well, I myself have no idea. It could also indicate a bug in the uic code.

But let's CC some people responsible for this code. Pekka recently added 
this WARN that triggers in your case; David and Paul look to be the 
people most involved in the uic code.

Start of the thread is at http://lkml.org/lkml/2009/6/20/165.

Cheers,
FJP
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