Re: client lookup_revalidate bug

["Benjamin Coddington" <bcodding@redhat.com>]

On 29 May 2019, at 12:21, Trond Myklebust wrote:

> 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'.

That was deliberate to avoid having to show two clients in the example..
sorry, I should have been more explicit.

I think the client should be able to detect this case, since it can see an
updated change_attr for that particular directory -- that is
"/mnt/two/B/foo", but maybe it needs to compare the change_attr to its
previous value instead of comparing it to the child's d_time?

The person who reported it has some workload that flips files between
directories on separate clients, and doesn't like it when `mv` reports
"source and destination are the same file".

Ben