Re: [PATCH 01/14] iomap: iomap that extends beyond EOF should be marked dirty

[Darrick J. Wong]

On Thu, Oct 17, 2019 at 07:56:11PM +0200, Christoph Hellwig wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> When doing a direct IO that spans the current EOF, and there are
> written blocks beyond EOF that extend beyond the current write, the
> only metadata update that needs to be done is a file size extension.
> 
> However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
> there is IO completion metadata updates required, and hence we may
> fail to correctly sync file size extensions made in IO completion
> when O_DSYNC writes are being used and the hardware supports FUA.
> 
> Hence when setting IOMAP_F_DIRTY, we need to also take into account
> whether the iomap spans the current EOF. If it does, then we need to
> mark it dirty so that IO completion will call generic_write_sync()
> to flush the inode size update to stable storage correctly.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Looks ok, but need fixes tag.  Also, might it be wise to split off the
ext4 section into a separate patch so that it can be backported
separately?

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

--D

> ---
>  fs/ext4/inode.c       | 9 ++++++++-
>  fs/xfs/xfs_iomap.c    | 7 +++++++
>  include/linux/iomap.h | 2 ++
>  3 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 516faa280ced..e9dc52537e5b 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3523,9 +3523,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  			return ret;
>  	}
>  
> +	/*
> +	 * Writes that span EOF might trigger an IO size update on completion,
> +	 * so consider them to be dirty for the purposes of O_DSYNC even if
> +	 * there is no other metadata changes being made or are pending here.
> +	 */
>  	iomap->flags = 0;
> -	if (ext4_inode_datasync_dirty(inode))
> +	if (ext4_inode_datasync_dirty(inode) ||
> +	    offset + length > i_size_read(inode))
>  		iomap->flags |= IOMAP_F_DIRTY;
> +
>  	iomap->bdev = inode->i_sb->s_bdev;
>  	iomap->dax_dev = sbi->s_daxdev;
>  	iomap->offset = (u64)first_block << blkbits;
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index f780e223b118..32993c2acbd9 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1049,6 +1049,13 @@ xfs_file_iomap_begin(
>  	trace_xfs_iomap_alloc(ip, offset, length, XFS_DATA_FORK, &imap);
>  
>  out_finish:
> +	/*
> +	 * Writes that span EOF might trigger an IO size update on completion,
> +	 * so consider them to be dirty for the purposes of O_DSYNC even if
> +	 * there is no other metadata changes pending or have been made here.
> +	 */
> +	if ((flags & IOMAP_WRITE) && offset + length > i_size_read(inode))
> +		iomap->flags |= IOMAP_F_DIRTY;
>  	return xfs_bmbt_to_iomap(ip, iomap, &imap, shared);
>  
>  out_found:
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 7aa5d6117936..24bd227d59f9 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -32,6 +32,8 @@ struct vm_fault;
>   *
>   * IOMAP_F_DIRTY indicates the inode has uncommitted metadata needed to access
>   * written data and requires fdatasync to commit them to persistent storage.
> + * This needs to take into account metadata changes that *may* be made at IO
> + * completion, such as file size updates from direct IO.
>   */
>  #define IOMAP_F_NEW		0x01	/* blocks have been newly allocated */
>  #define IOMAP_F_DIRTY		0x02	/* uncommitted metadata */
> -- 
> 2.20.1
>