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

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Message-ID: <20131106203429.GL5661@alberich>
Date:	Wed, 6 Nov 2013 21:34:30 +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 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.

> > Are you sure that this fixes the issue? Looks like the
> > kmem_cache_flag function should fail regardless of how early you set it.
> > 
> > AFAICT the right fix would be:
> 
> That would avoid the panic but I guess it won't enable slub debugging.

Ok, the latter is bogus. Of course debugging is switched on.

> However I'll test this.

Your patch fixed it.


Andreas
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