On Wed, Dec 20, 2017 at 3:09 AM, Chengguang Xu <cgxu519@xxxxxxxxxx> wrote:
> Inspired by encountering unexpected write error with
> error code -EXDEV when upperdir and workdir having
> different project quotas. The reason of the error is
> project quota asks files in it strictly inherit
> project id of it’s own, so rename/link operations
> between those directories will fail and it may cause
> failure during copy-up/index-link operations in overlayfs.
>
> So if upper filesystem supports O_TMPFILE, try to check
> link ability between upperdir and workdir and if check
> fails, print a proper warning message to indicate potential
> possibility of write failure.
>
> The failure of the check does not directly lead to
> read-only mounting because in some use cases may only
> write to upperdir and do not modify anything in lowerdirs.
>
> Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxx>
> ---
> Changes since v3:
> - Add more detail comment about motivation to changelog.
>
> Changes since v2:
> - Add comment about motivation.
> - Modify warning message.
>
> Changes since v1:
> - Check link ablity between upperdir and workdir instead of checking
> project ids of upperdir and workdir.
> - Print a warning message instead of falling to readonly mode.
>
> fs/overlayfs/super.c | 30 +++++++++++++++++++++++-------
> 1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 76440fe..7d6bd82 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -929,7 +929,7 @@ static int ovl_get_upper(struct ovl_fs *ofs, struct path *upperpath)
>
> static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
> {
> - struct dentry *temp;
> + struct dentry *uppertemp, *worktemp;
> int err;
>
> ofs->workdir = ovl_workdir_create(ofs, OVL_WORKDIR_NAME, false);
> @@ -953,12 +953,28 @@ static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
> if (!err)
> pr_warn("overlayfs: upper fs needs to support d_type.\n");
>
> - /* Check if upper/work fs supports O_TMPFILE */
> - temp = ovl_do_tmpfile(ofs->workdir, S_IFREG | 0);
> - ofs->tmpfile = !IS_ERR(temp);
> - if (ofs->tmpfile)
> - dput(temp);
> - else
> + /*
> + * Check if upper/work fs supports O_TMPFILE and if support, check
> + * link ability between upperdir and workdir, this is inspired by
> + * encountering unexpected write error when upperdir and workdir
> + * having different project ids.
> + */
> + uppertemp = ovl_do_tmpfile(ofs->upper_mnt->mnt_root, S_IFREG | 0);
> + ofs->tmpfile = !IS_ERR(uppertemp);
> + if (ofs->tmpfile) {
> + worktemp = ovl_lookup_temp(ofs->workdir);
Have you tested this? Because there's a warning at the top of
lookup_one_len() that triggers because of no locking of parent.
I can add the locking, it's trivial, but I'd still like you to test
this on your setup, if it actually does what you promise it does.
Thanks,
Miklos
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