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

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Message-ID: <20131106211604.GM5661@alberich>
Date:	Wed, 6 Nov 2013 22:16:04 +0100
From:	Andreas Herrmann <andreas.herrmann@...xeda.com>
To:	Christoph Lameter <cl@...ux.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 Wed, Nov 06, 2013 at 09:34:29PM +0100, Andreas Herrmann wrote:
> On Wed, Nov 06, 2013 at 08:54:17PM +0100, Andreas Herrmann wrote:
> > On Wed, Nov 06, 2013 at 02:16:33PM -0500, Christoph Lameter wrote:
> > > On Wed, 6 Nov 2013, Andreas Herrmann wrote:
> > > 
> > > > When I've used slub_debug kernel option (e.g.
> > > > "slub_debug=,skbuff_fclone_cache" or similar) on a debug session I've
> > > > seen a panic like:
> > > 
> > > Hmmm.. That looks like its due to some slabs not having names
> > > during early boot. kmem_cache_flags is called with NULL as a parameter.
> > 
> > That's because the slub_debug parameter is not evaluated before
> > kmem_cache_flags is called.
> > 
> > Older kernels didn't show this problem. I think the sequence of those
> > calls has changed. Not sure what patch set has made that change.
> 
> Please ignore this comment.
> I revisisted the code and of course you are right.
> Hmm, now wondering why my patch covered the panic.

Arrgh, my patch changed slub_debug_slabs to be NULL.
That is why the panic didn't happen.

Would be nice, if your patch is pushed upstream asap.


Thanks,

Andreas
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