Locking issue between NFSv4 and SMB client

dai.ngo
2021-07-15T23:45:33Z

Hi Bruce,

I'm doing some locking testing between NFSv4 and SMB client and
think there are some issues on the server that allows both clients
to lock the same file at the same time.

Here is what I did:

NOTE: lck is a simple program that use lockf(3) to lock a file from
offset 0 to the length specified by '-l'.

On NFSv4 client
---------------

[root@nfsvmd07 ~]# nfsstat -m
/tmp/mnt from nfsvmf24:/root/smb_share
Flags: rw,relatime,vers=4.1,rsize=1048576,wsize=1048576,namlen=255,hard,
proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.80.62.47,
local_lock=none,addr=10.80.111.94
[root@nfsvmd07 ~]#

[root@nfsvmd07 ~]# ./lck -p /tmp/mnt/messages -W -l 100000000
Lck/file: 1, Maxlocks: 10000000
Locking[/tmp/mnt/messages] Offset[0] Len[100000000] N[0]...doing F_LOCK..
LOCKED...

Locks[1] files[1] took[2.000s] sleep waiting...Hit Control-C to stop

[NFS client successfully locks the file]

On SMB client
-------------

[root@nfsvme24 ~]# mount |grep cifs
//nfsvmf24/smb_share on /tmp/mnt type cifs (rw,relatime,vers=3.1.1,cache=strict,username=root,uid=0,noforceuid,gid=0,noforcegid,addr=10.80.111.94,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,echo_interval=60,actimeo=1)
[root@nfsvme24 ~]#

[root@nfsvme24 ~]# smbclient -L nfsvmf24
Enter SAMBA\root's password:

Sharename Type Comment
--------- ---- -------
print$ Disk Printer Drivers
smb_share Disk Test Samba Share <<===== share to mount
IPC$ IPC IPC Service (Samba 4.10.16)
root Disk Home Directories
Reconnecting with SMB1 for workgroup listing.

Server Comment
--------- -------

Workgroup Master
--------- -------
[root@nfsvme24 ~]#

[root@nfsvme24 ~]# ./lck -p /tmp/mnt/messages -W -l 100000000
Lck/file: 1, Maxlocks: 10000000
Locking[/tmp/mnt/messages] Offset[0] Len[100000000] N[0]...doing F_LOCK..
LOCKED...

Locks[1] files[1] took[2.000s] sleep waiting...Hit Control-C to stop

[SMB client successfully locks the file]

The same issue happens when either client locks the file first.
I think this is what has happened:

1. NFSv4 client opens and locks the file first

. NFSv4 client send OPEN and LOCK to server, server replies
OK on both requests.

. SMB client sends create request with Oplock==Lease for
the same file.

. server holds off on replying to SMB client's create request,
recalls delegation from NFSv4 client, waits for NFSv4 client
to return the delegation then replies success to SMB client's
create request with lease granted (Oplock==Lease).

NOTE: I think SMB server should replies the create request
with Oplock==None to force the SMB client to sends the
lock request.

. Once SMB client receives the reply of the create with
'Oplock==Lease', it assumes it has full control of the file
therefor it does not need to send the lock request.

. both NFSv4 and SMB client now think they have locked the file.

pcap: nfs_lock_smb_lock.pcap

2. SMB client creates the file with 'Oplock==Lease' first

. SMB sends create request with 'Oplock==Lease' to server,
server replies OK with 'Oplock==Lease'. SMB client skips
sending lock request since it assumes it has full control
of the file with the lease.

. NFSv4 client sends OPEN to server, server replies OK with
delagation is none. NFSv4 client sends LOCK request, since
no lock was created in the kernel for the SMB client, the
lock was granted to the NFSv4 client.

NOTE: I think the SMB server should send lease break
notification to the SMB client, wait for the lease break
acknowledgment from SMB client before replying to the
OPEN of the NFSv4 client. This will force the SMB client
to send the lock request to the server.

. both NFSv4 and SMB client now think they have locked the file.

Your thought?

Thanks,

-Dai