Description of problem:

The struct file_operations (include/linux/fs.h) has "lock" 
defineds: 

int (*lock) (struct file *, int, struct file_lock *);

and system call interfaces (sys_fcntl and sys_flock) have 
been calling this interface to invoke filesystem specific 
lock functions. Unfortunately, NLM and NFS v4 code, using
posix_lock_file() VFS call, do not follow this (i.e., they
do not invoke f_op->lock in the code patch at all).

This may not be an issue for local filesystem such as ext3 
(that doesn't define its own "lock" method) but it is a 
nontrivial function flaw for cluster filesystem such as GFS. 
The implication here is that GFS can't do file locking 
across different nodes if accessed from NFS export.  

Version-Release number of selected component (if applicable):
All NLM and NFS v4 code within RHEL versions, including 
upstream kernels. 

How reproducible:
Each time and every time


Steps to Reproduce:
1. Export GFS share via NFS
2. Lock the file via fcntl() from different NFS clients
  
Actual results:
The lock calls completes. 

Expected results:
For exclusive locks such as F_WRLCK, only one call 
should go thru. 

Additional info:
Note that the result is correct if the file is locked via
local access (i.e., invoking fcntl() directly from different 
GFS nodes). In simple words, the VFS layer behaves correctly
but not NLM and NFS v4 code.