linux-kernel - Re: [PATCH] mm/slub: Switch slub_debug kernel option to early

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Date:	Thu, 7 Nov 2013 16:09:15 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Andreas Herrmann <andreas.herrmann@...xeda.com>
cc:	Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/slub: Switch slub_debug kernel option to early_param
 to avoid boot panic

On Thu, 7 Nov 2013, Andreas Herrmann wrote:

> And for sake of completeness. Here is some debug output with a kernel
> that had your "slub: Handle NULL parameter in kmem_cache_flags" patch
> applied. And of course there were a couple of unnamed slabs:
>
>   ...
>          .bss : 0xc089fd80 - 0xc094cc4c   ( 692 kB)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (c06fc90c): kmem_cache_node
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (c06fc91c): kmem_cache
> → slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   slub_debug_slabs (c2956a08): skbuff_fclone_cache, name (  (null)): (null)
>   SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
>   ...

Well yes on bootstrap the slabs are initially created without a name.
Later the name is provided. Before the introduction of the common kmalloc
code the kmalloc caches had a generic name instead of NULL. I was not sure
that this was a valid thing to do so I put NULL in there so that we can
catch the uses.