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

Darrick J. Wong
2019-10-17T18:41:45Z

On Thu, Oct 17, 2019 at 07:56:11PM +0200, Christoph Hellwig wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> 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@redhat.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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@oracle.com>

--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
>