Re: [PATCH] mm/slub: Switch slub_debug kernel option to early_paramto avoid boot panic
From: Andreas Herrmann
Date: Wed Nov 06 2013 - 14:54:28 EST
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.
> 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.
However I'll test this.
> Subject: slub: Handle NULL parameter in kmem_cache_flags
> kmem_cache_flags may be called with NULL parameter during early boot.
> Skip the test in that case.
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
> Index: linux/mm/slub.c
> --- linux.orig/mm/slub.c 2013-10-15 13:55:44.000000000 -0500
> +++ linux/mm/slub.c 2013-11-06 13:09:21.810583134 -0600
> @@ -1217,7 +1217,7 @@ static unsigned long kmem_cache_flags(un
> * Enable debugging if selected on the kernel commandline.
> - if (slub_debug && (!slub_debug_slabs ||
> + if (slub_debug && name && (!slub_debug_slabs ||
> !strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs))))
> flags |= slub_debug;
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