RE: [PATCH v2] exfat: call sync_filesystem for read-only remount

["Sungjong Seo" <sj1557.seo@samsung.com>]

> We need to commit dirty metadata and pages to disk before remounting exfat
> as read-only.
> 
> This fixes a failure in xfstests generic/452
> 
> generic/452 does the following:
> cp something <exfat>/
> mount -o remount,ro <exfat>
> 
> the <exfat>/something is corrupted. because while exfat is remounted as
> read-only, exfat doesn't have a chance to commit metadata and vfs
> invalidates page caches in a block device.
> 
> Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>

Acked-by: Sungjong Seo <sj1557.seo@samsung.com>

> ---
> Changes from v1:
> - Does not check the return value of sync_filesystem to
>   allow to change from "rw" to "ro" even when this function
>   fails.
> - Add the detailed explanation why generic/452 fails
> 
>  fs/exfat/super.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/exfat/super.c b/fs/exfat/super.c index
> e650e65536f8..253a92460d52 100644
> --- a/fs/exfat/super.c
> +++ b/fs/exfat/super.c
> @@ -693,10 +693,20 @@ static void exfat_free(struct fs_context *fc)
>  	}
>  }
> 
> +static int exfat_reconfigure(struct fs_context *fc) {
> +	fc->sb_flags |= SB_NODIRATIME;
> +
> +	/* volume flag will be updated in exfat_sync_fs */
> +	sync_filesystem(fc->root->d_sb);
> +	return 0;
> +}
> +
>  static const struct fs_context_operations exfat_context_ops = {
>  	.parse_param	= exfat_parse_param,
>  	.get_tree	= exfat_get_tree,
>  	.free		= exfat_free,
> +	.reconfigure	= exfat_reconfigure,
>  };
> 
>  static int exfat_init_fs_context(struct fs_context *fc)
> --
> 2.17.1