ext4: Implement swap_activate aops using iomap

After moving ext4's bmap to iomap interface, swapon functionality
on files created using fallocate (which creates unwritten extents) are
failing. This is since iomap_bmap interface returns 0 for unwritten
extents and thus generic_swapfile_activate considers this as holes
and hence bail out with below kernel msg :-

[340.915835] swapon: swapfile has holes

To fix this we need to implement ->swap_activate aops in ext4
which will use ext4_iomap_report_ops. Since we only need to return
the list of extents so ext4_iomap_report_ops should be enough.

Reported-by: Yuxuan Shui <yshuiv7@gmail.com>
Fixes: ac58e4fb03f ("ext4: move ext4 bmap to use iomap infrastructure")
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
---
[Tested xfstests with -g swap; Tested stress-ng with --thrash option]

 fs/ext4/inode.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

On Fri, Sep 04, 2020 at 02:46:53PM +0530, Ritesh Harjani wrote:
> After moving ext4's bmap to iomap interface, swapon functionality
> on files created using fallocate (which creates unwritten extents) are
> failing. This is since iomap_bmap interface returns 0 for unwritten
> extents and thus generic_swapfile_activate considers this as holes
> and hence bail out with below kernel msg :-
> 
> [340.915835] swapon: swapfile has holes
> 
> To fix this we need to implement ->swap_activate aops in ext4
> which will use ext4_iomap_report_ops. Since we only need to return
> the list of extents so ext4_iomap_report_ops should be enough.
> 
> Reported-by: Yuxuan Shui <yshuiv7@gmail.com>
> Fixes: ac58e4fb03f ("ext4: move ext4 bmap to use iomap infrastructure")
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
> ---
> [Tested xfstests with -g swap; Tested stress-ng with --thrash option]

Seems reasonable to me (at least from the iomap and "did you run QA?"
end...)

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> 
>  fs/ext4/inode.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 1556cabd3a7d..9ac0f83e6fbe 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3605,6 +3605,13 @@ static int ext4_set_page_dirty(struct page *page)
>  	return __set_page_dirty_buffers(page);
>  }
>  
> +static int ext4_iomap_swap_activate(struct swap_info_struct *sis,
> +				    struct file *file, sector_t *span)
> +{
> +	return iomap_swapfile_activate(sis, file, span,
> +				       &ext4_iomap_report_ops);
> +}
> +
>  static const struct address_space_operations ext4_aops = {
>  	.readpage		= ext4_readpage,
>  	.readpages		= ext4_readpages,
> @@ -3620,6 +3627,7 @@ static const struct address_space_operations ext4_aops = {
>  	.migratepage		= buffer_migrate_page,
>  	.is_partially_uptodate  = block_is_partially_uptodate,
>  	.error_remove_page	= generic_error_remove_page,
> +	.swap_activate		= ext4_iomap_swap_activate,
>  };
>  
>  static const struct address_space_operations ext4_journalled_aops = {
> @@ -3636,6 +3644,7 @@ static const struct address_space_operations ext4_journalled_aops = {
>  	.direct_IO		= noop_direct_IO,
>  	.is_partially_uptodate  = block_is_partially_uptodate,
>  	.error_remove_page	= generic_error_remove_page,
> +	.swap_activate		= ext4_iomap_swap_activate,
>  };
>  
>  static const struct address_space_operations ext4_da_aops = {
> @@ -3653,6 +3662,7 @@ static const struct address_space_operations ext4_da_aops = {
>  	.migratepage		= buffer_migrate_page,
>  	.is_partially_uptodate  = block_is_partially_uptodate,
>  	.error_remove_page	= generic_error_remove_page,
> +	.swap_activate		= ext4_iomap_swap_activate,
>  };
>  
>  static const struct address_space_operations ext4_dax_aops = {
> @@ -3661,6 +3671,7 @@ static const struct address_space_operations ext4_dax_aops = {
>  	.set_page_dirty		= noop_set_page_dirty,
>  	.bmap			= ext4_bmap,
>  	.invalidatepage		= noop_invalidatepage,
> +	.swap_activate		= ext4_iomap_swap_activate,
>  };
>  
>  void ext4_set_aops(struct inode *inode)
> -- 
> 2.25.1
>

On Fri, Sep 04, 2020 at 02:46:53PM +0530, Ritesh Harjani wrote:
> After moving ext4's bmap to iomap interface, swapon functionality
> on files created using fallocate (which creates unwritten extents) are
> failing. This is since iomap_bmap interface returns 0 for unwritten
> extents and thus generic_swapfile_activate considers this as holes
> and hence bail out with below kernel msg :-
> 
> [340.915835] swapon: swapfile has holes
> 
> To fix this we need to implement ->swap_activate aops in ext4
> which will use ext4_iomap_report_ops. Since we only need to return
> the list of extents so ext4_iomap_report_ops should be enough.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

On Fri, Sep 04, 2020 at 02:46:53PM +0530, Ritesh Harjani wrote:
> After moving ext4's bmap to iomap interface, swapon functionality
> on files created using fallocate (which creates unwritten extents) are
> failing. This is since iomap_bmap interface returns 0 for unwritten
> extents and thus generic_swapfile_activate considers this as holes
> and hence bail out with below kernel msg :-
> 
> [340.915835] swapon: swapfile has holes
> 
> To fix this we need to implement ->swap_activate aops in ext4
> which will use ext4_iomap_report_ops. Since we only need to return
> the list of extents so ext4_iomap_report_ops should be enough.
> 
> Reported-by: Yuxuan Shui <yshuiv7@gmail.com>
> Fixes: ac58e4fb03f ("ext4: move ext4 bmap to use iomap infrastructure")
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>

Thanks, applied.

					- Ted