Re: client lookup_revalidate bug

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2019-05-29 at 11:08 -0400, Benjamin Coddington wrote:
> Hey, here's an interesting one, this seems wrong:
> 
> [root@fedora27_c2_v5 ~]# mkdir /mnt/one
> [root@fedora27_c2_v5 ~]# mkdir /mnt/two
> [root@fedora27_c2_v5 ~]# mount -t nfs -ov4,noac,sec=sys,nosharecache 
> 192.168.122.50:/exports /mnt/one
> [root@fedora27_c2_v5 ~]# mount -t nfs -ov4,noac,sec=sys,nosharecache 
> 192.168.122.50:/exports /mnt/two
> [root@fedora27_c2_v5 ~]# mkdir /mnt/one/A
> [root@fedora27_c2_v5 ~]# mkdir /mnt/one/B
> [root@fedora27_c2_v5 ~]# touch /mnt/one/A/foo
> [root@fedora27_c2_v5 ~]# cat /mnt/two/A/foo
> [root@fedora27_c2_v5 ~]# mv /mnt/two/A/foo /mnt/two/B/foo
> [root@fedora27_c2_v5 ~]# mv /mnt/one/B/foo /mnt/one/A/foo
> [root@fedora27_c2_v5 ~]# cat /mnt/two/A/foo
> [root@fedora27_c2_v5 ~]# stat /mnt/two/B/foo
>    File: /mnt/two/B/foo
>    Size: 0         	Blocks: 0          IO Block: 262144 regular
> empty 
> file
> Device: 2fh/47d	Inode: 439603      Links: 1
> Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid:
> (    0/    root)
> Context: system_u:object_r:nfs_t:s0
> Access: 2019-05-28 14:00:18.929663705 -0400
> Modify: 2019-05-28 14:00:18.929663705 -0400
> Change: 2019-05-28 14:00:58.990124573 -0400
>   Birth: -
> 
> 
> ^^ that lstat should return -ENOENT.
> 
> I think we detect a stale directory by comparing the directory's 
> change_attr with the dentry's d_time.  But, here's a case where they
> are 
> the same!
> 
> Am I wrong about this, or any clever ideas to catch this case?
> 

When you are mounting using 'nosharecache' then you are making /mnt/one
and /mnt/two act as if they are different filesystems. The fact that
they are the same on the server, means you are setting up a testcase
where the files+directories are acting like the "changing on the
server" case as far as the client is concerned.

If you want the above to work in a sane fashion, then just don't use
'nosharecache'.

Cheers
   Trond

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com