Re: [PATCH v2 1/3] s390/numa: set node distance to LOCAL_DISTANCE

[Heiko Carstens <hca@linux.ibm.com>]

On Tue, Aug 04, 2020 at 08:35:49PM +0200, Alexander Gordeev wrote:
> The node distance is hardcoded to 0, which causes a trouble
> for some user-level applications. In particular, "libnuma"
> expects the distance of a node to itself as LOCAL_DISTANCE.
> This update removes the offending node distance override.
> 
> Cc: <stable@vger.kernel.org> # v5.6+
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Fixes: 701dc81e7412 ("s390/mm: remove fake numa support")
> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
> ---
>  arch/s390/include/asm/topology.h | 6 ------
>  1 file changed, 6 deletions(-)

It would have been nice if the Fixes tag would be correct, since then
there would be hardly any backport necessary. But unfortunately this
is broken since we support numa.

Older code had this:

int __node_distance(int a, int b)
{
	return mode->distance ? mode->distance(a, b) : 0;
}
EXPORT_SYMBOL(__node_distance);

And the distance function was only set for the emulation mode, but not
the default ("plain") mode.

I'll change that in the commit message.