Re: [PATCH] selftests/mm: Fix BUG_ON checking wrong variable in mremap_dontunmap

["David Hildenbrand (Arm)" <david@kernel.org>]

On 7/17/26 09:02, Hongfu Li wrote:
> From: Hongfu Li <lihongfu@kylinos.cn>
> 
> In mremap_dontunmap_partial_mapping_overwrite(), mremap() stores its
> returned remapped address into remapped_mapping, while the BUG_ON
> incorrectly checks dest_mapping instead.
> 
> If mremap() fails, dest_mapping still holds a valid pointer obtained from
> the prior mmap() call, making this BUG_ON never trigger at all. Correct
> the check to validate the actual mremap() return value stored in
> remapped_mapping.
> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> ---
>  tools/testing/selftests/mm/mremap_dontunmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/mremap_dontunmap.c b/tools/testing/selftests/mm/mremap_dontunmap.c
> index a4f75d836733..96ba537facf7 100644
> --- a/tools/testing/selftests/mm/mremap_dontunmap.c
> +++ b/tools/testing/selftests/mm/mremap_dontunmap.c
> @@ -313,7 +313,7 @@ static void mremap_dontunmap_partial_mapping_overwrite(void)
>  	    mremap(source_mapping, 5 * page_size,
>  		   5 * page_size,
>  		   MREMAP_DONTUNMAP | MREMAP_MAYMOVE | MREMAP_FIXED, dest_mapping);
> -	BUG_ON(dest_mapping == MAP_FAILED, "mremap");
> +	BUG_ON(remapped_mapping == MAP_FAILED, "mremap");
>  	BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");

Given that we know from a previous

	BUG_ON(dest_mapping == MAP_FAILED, "mmap");

We can just drop this line completely and rely on the

	BUG_ON(dest_mapping != remapped_mapping, "expected to remap to dest_mapping");

-- 
Cheers,

David