Re: [PATCH] iomap: fsync swap files before iterating mappings

[Christoph Hellwig <hch@infradead.org>]

On Tue, Jun 05, 2018 at 09:16:05AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Swap files require that all the file mapping metadata be stable on disk.
> It is insufficient to flush dirty pages in the page cache because that
> won't necessarily result in filesystems pushing all their metadata out
> to disk.  Therefore, call fsync from iomap_swapfile_activate.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/iomap.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 206539d369a8..48622bbbd751 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -1387,7 +1387,11 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
>  	loff_t len = ALIGN_DOWN(i_size_read(inode), PAGE_SIZE);
>  	loff_t ret;
>  
> -	ret = filemap_write_and_wait(inode->i_mapping);
> +	/*
> +	 * Persist all file mapping metadata so that we won't have any
> +	 * IOMAP_F_DIRTY iomaps.
> +	 */
> +	ret = vfs_fsync(swap_file, 0);

datasync semantics should be more than enough, so you can pass 1 here..