On 06/26/24 at 01:43pm, Uladzislau Rezki (Sony) wrote:
> The problem is that there are systems where cpu_possible_mask
> has gaps between set CPUs, for example SPARC. In this scenario
> addr_to_vb_xa() hash function can return an index which accesses
> to not-possible and not setup CPU area using per_cpu() macro.
>
> A per-cpu vmap_block_queue is also used as hash table assuming
~~~~~
> that incorrectly assumes the cpu_possible_mask has not gaps.
~~~~~~
Typo of duplicated word?
Other than above nit, this looks good to me. Thanks.
Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
>
> Fix it by adjusting an index to a next possible CPU.
>
> Fixes: 062eacf57ad9 ("mm: vmalloc: remove a global vmap_blocks xarray")
> Reported-by: Nick Bowler <nbowler@xxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-kernel/ZntjIE6msJbF8zTa@MiWiFi-R3L-srv/T/
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
> mm/vmalloc.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index b4c42da9f3901..6b783baf12a14 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2544,7 +2544,15 @@ static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue);
> static struct xarray *
> addr_to_vb_xa(unsigned long addr)
> {
> - int index = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus();
> + int index = (addr / VMAP_BLOCK_SIZE) % nr_cpu_ids;
> +
> + /*
> + * Please note, nr_cpu_ids points on a highest set
> + * possible bit, i.e. we never invoke cpumask_next()
> + * if an index points on it which is nr_cpu_ids - 1.
> + */
> + if (!cpu_possible(index))
> + index = cpumask_next(index, cpu_possible_mask);
>
> return &per_cpu(vmap_block_queue, index).vmap_blocks;
> }
> --
> 2.39.2
>
