Re: [PATCH v7 02/20] fs/dax: Return unmapped busy pages from dax_layout_busy_page_range()

[Balbir Singh]

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@xxxxxxxxxx>
> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  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@xxxxxxxxxx>