Re: [PATCH 3/3] xen/common: Add NUMA node id bounds check to page_alloc.c/node_to_scrub

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Adding Henry as this issue is currently causing gitlab-ci failures. I
think we should fix it as soon as possible to get clearer results for
the 4.18 release. (This comment applies to the rest of the series as
well).


On Mon, 25 Sep 2023, Shawn Anastasio wrote:
> When building for Power with CONFIG_DEBUG unset, a compiler error gets
> raised inside page_alloc.c's node_to_scrub function, likely due to the
> increased optimization level:
> 
> common/page_alloc.c: In function 'node_to_scrub.part.0':
> common/page_alloc.c:1217:29: error: array subscript 1 is above array
>             bounds of 'long unsigned int[1]' [-Werror=array-bounds]
>  1217 |         if ( node_need_scrub[node] )
> 
> It appears that this is a false positive, given that in practice
> cycle_node should never return a node ID >= MAX_NUMNODES as long as the
> architecture's node_online_map is properly defined and initialized, so
> this additional bounds check is only to satisfy GCC.
> 
> Signed-off-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  xen/common/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 35d9a26fa6..6df2a223e1 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1211,6 +1211,9 @@ static unsigned int node_to_scrub(bool get_node)
>          } while ( !cpumask_empty(&node_to_cpumask(node)) &&
>                    (node != local_node) );
> 
> +        if ( node >= MAX_NUMNODES )
> +            break;
> +
>          if ( node == local_node )
>              break;
> 
> --
> 2.30.2
>