Re: [PATCH] mm/memblock: WARN_ON when nid differs from overlap region

[David Rientjes <rientjes@google.com>]

On Wed, 8 Jul 2015, Wei Yang wrote:

> Each memblock_region has nid to indicates the Node ID of this range. For
> the overlap case, memblock_add_range() inserts the lower part and leave the
> upper part as indicated in the overlapped region.
> 
> If the nid of the new range differs from the overlapped region, the
> information recorded is not correct.
> 
> This patch adds a WARN_ON when the nid of the new range differs from the
> overlapped region.
> 
> ---
> 
> I am not familiar with the lower level topology, maybe this case will not
> happen. 
> 
> If current implementation is based on the assumption, that overlapped
> ranges' nid and flags are the same, I would suggest to add a comment to
> indicates this background.
> 
> If the assumption is not correct, I suggest to add a WARN_ON or BUG_ON to
> indicates this case.
> 
> Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
> ---
>  mm/memblock.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 9318b56..09efe70 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -540,6 +540,9 @@ repeat:
>  		 * area, insert that portion.
>  		 */
>  		if (rbase > base) {
> +#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
> +			WARN_ON(nid != memblock_get_region_node(rgn));
> +#endif
>  			nr_new++;
>  			if (insert)
>  				memblock_insert_region(type, i++, base,

I think the assertion that nid should match memblock_get_region_node() of 
the overlapped region is correct.  It only functionally makes a difference 
if insert == true, but I don't think there's harm in verifying it 
regardless.

Acked-by: David Rientjes <rientjes@google.com>

I think your supplemental to the changelog suggests that you haven't seen 
this actually occur, but in the off chance that you have then it would be 
interesting to see it.

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