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

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

[Hongfu Li]

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");
 
 	BUG_ON(check_region_contains_byte(source_mapping, 5 * page_size, 0) !=
-- 
2.54.0

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

[SJ Park]

On Fri, 17 Jul 2026 15:02:51 +0800 Hongfu Li <hongfu.li@linux.dev> 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.

Nice catch.

> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]