Re: [PATCH] mm/slub: Switch slub_debug kernel option to early_param to avoid boot panic

[Andreas Herrmann <andreas.herrmann@calxeda.com>]

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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