>
> 在 2018年1月20日，上午12:25，Miklos Szeredi <miklos@xxxxxxxxxx> 写道：
>
> 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.
Hi Miklos,
Sorry that I could not reproduce it on my setup for the patch because
the test vm has already reclaimed, but I can see the warning in my new
test vm, so I guess maybe ‘DEBUG_BUGVERBOSE’ configuration was not
properly set in the previous test setup.
Thanks,
Chengguang.
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