On 2/5/25 09:47, Alistair Popple wrote:
> dax_layout_busy_page_range() is used by file systems to scan the DAX
> page-cache to unmap mapping pages from user-space and to determine if
> any pages in the given range are busy, either due to ongoing DMA or
> other get_user_pages() usage.
>
> Currently it checks to see the file mapping is mapped into user-space
> with mapping_mapped() and returns early if not, skipping the check for
> DMA busy pages. This is wrong as pages may still be undergoing DMA
> access even if they have subsequently been unmapped from
> user-space. Fix this by dropping the check for mapping_mapped().
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/dax.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 21b4740..5133568 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -690,7 +690,7 @@ struct page *dax_layout_busy_page_range(struct address_space *mapping,
> if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
> return NULL;
>
> - if (!dax_mapping(mapping) || !mapping_mapped(mapping))
> + if (!dax_mapping(mapping))
> return NULL;
>
> /* If end == LLONG_MAX, all pages from start to till end of file */
I think the patch should probably also add
if (mapping_mapped(mapping))
unmap_mapping_pages(mapping, start_idx, end_idx - start_idx + 1, 0);
But I don't think it's a blocker unmap_mapping_pages() should do the right thing internally
Acked-by: Balbir Singh <balbirs@nvidia.com>