Re: [PATCH v7 04/14] xfs, dax: introduce xfs_dax_aops

[Jan Kara]

On Wed 21-03-18 15:57:32, Dan Williams wrote:
> In preparation for the dax implementation to start associating dax pages
> to inodes via page->mapping, we need to provide a 'struct
> address_space_operations' instance for dax. Otherwise, direct-I/O
> triggers incorrect page cache assumptions and warnings like the
> following:
> 
>  WARNING: CPU: 27 PID: 1783 at fs/xfs/xfs_aops.c:1468
>  xfs_vm_set_page_dirty+0xf3/0x1b0 [xfs]
>  [..]
>  CPU: 27 PID: 1783 Comm: dma-collision Tainted: G           O 4.15.0-rc2+ #984
>  [..]
>  Call Trace:
>   set_page_dirty_lock+0x40/0x60
>   bio_set_pages_dirty+0x37/0x50
>   iomap_dio_actor+0x2b7/0x3b0
>   ? iomap_dio_zero+0x110/0x110
>   iomap_apply+0xa4/0x110
>   iomap_dio_rw+0x29e/0x3b0
>   ? iomap_dio_zero+0x110/0x110
>   ? xfs_file_dio_aio_read+0x7c/0x1a0 [xfs]
>   xfs_file_dio_aio_read+0x7c/0x1a0 [xfs]
>   xfs_file_read_iter+0xa0/0xc0 [xfs]
>   __vfs_read+0xf9/0x170
>   vfs_read+0xa6/0x150
>   SyS_pread64+0x93/0xb0
>   entry_SYSCALL_64_fastpath+0x1f/0x96
> 
> ...where the default set_page_dirty() handler assumes that dirty state
> is being tracked in 'struct page' flags.
> 
> Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
> Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/xfs/xfs_aops.c |   21 +++++++++++++++++----
>  fs/xfs/xfs_aops.h |    1 +
>  fs/xfs/xfs_iops.c |    5 ++++-
>  3 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 9c6a830da0ee..5f1f5948ecc2 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1194,16 +1194,22 @@ xfs_vm_writepages(
>  	int			ret;
>  
>  	xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
> -	if (dax_mapping(mapping))
> -		return dax_writeback_mapping_range(mapping,
> -				xfs_find_bdev_for_inode(mapping->host), wbc);
> -
>  	ret = write_cache_pages(mapping, wbc, xfs_do_writepage, &wpc);
>  	if (wpc.ioend)
>  		ret = xfs_submit_ioend(wbc, wpc.ioend, ret);
>  	return ret;
>  }
>  
> +STATIC int
> +xfs_dax_writepages(
> +	struct address_space	*mapping,
> +	struct writeback_control *wbc)
> +{
> +	xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
> +	return dax_writeback_mapping_range(mapping,
> +			xfs_find_bdev_for_inode(mapping->host), wbc);
> +}
> +
>  /*
>   * Called to move a page into cleanable state - and from there
>   * to be released. The page should already be clean. We always
> @@ -1505,3 +1511,10 @@ const struct address_space_operations xfs_address_space_operations = {
>  	.is_partially_uptodate  = block_is_partially_uptodate,
>  	.error_remove_page	= generic_error_remove_page,
>  };
> +
> +const struct address_space_operations xfs_dax_aops = {
> +	.direct_IO		= xfs_vm_direct_IO,
> +	.writepages		= xfs_dax_writepages,
> +	.set_page_dirty		= noop_set_page_dirty,
> +	.invalidatepage		= noop_invalidatepage,
> +};
> diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
> index 88c85ea63da0..69346d460dfa 100644
> --- a/fs/xfs/xfs_aops.h
> +++ b/fs/xfs/xfs_aops.h
> @@ -54,6 +54,7 @@ struct xfs_ioend {
>  };
>  
>  extern const struct address_space_operations xfs_address_space_operations;
> +extern const struct address_space_operations xfs_dax_aops;
>  
>  int	xfs_setfilesize(struct xfs_inode *ip, xfs_off_t offset, size_t size);
>  
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 56475fcd76f2..951e84df5576 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1272,7 +1272,10 @@ xfs_setup_iops(
>  	case S_IFREG:
>  		inode->i_op = &xfs_inode_operations;
>  		inode->i_fop = &xfs_file_operations;
> -		inode->i_mapping->a_ops = &xfs_address_space_operations;
> +		if (IS_DAX(inode))
> +			inode->i_mapping->a_ops = &xfs_dax_aops;
> +		else
> +			inode->i_mapping->a_ops = &xfs_address_space_operations;
>  		break;
>  	case S_IFDIR:
>  		if (xfs_sb_version_hasasciici(&XFS_M(inode->i_sb)->m_sb))
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR