Description of problem :
If an NFS client open a file over NFS, and then this file is modified on the 
server,when read the file on Client,the contents of file is wrong(Client can't 
get Server's modify).

Version-Release number of selected component (if applicable) :
RHEL4U5 (kernel-2.6.9-55.EL)
nfs-utils-1.0.6-80.EL4

How reproducible :
Use the following C program :
----------------------------------------------------------------
#include <stdio.h>
#include <fcntl.h>
int main()
{
    int  fd, ret;
    char readbuf[1024]="";
    char *sfile = "/mnt/testfile";
    printf("test start\n");
    if ((fd = open(s, O_CREAT|O_TRUNC|O_RDWR ,0700)) < 0) {
        printf("can't open file\n");
    exit(1);
    }
    printf("sleeping,please do echo operation on server.\n");
    sleep(60);
    ret = read(fd, readbuf, 1024);
    printf("read: %s\n",readbuf);
    close(fd);
    printf("test end\n");
}
----------------------------------------------------------------

Reproduce Environment :
Server: 192.168.1.2
        showmount -e : /tmp *
Client: 192.168.1.1

Steps to Reproduce :
1. On Client :
   mount -t nfs4 192.168.1.2:/ /mnt
2. On Client :
   run above C program
3. On Server :
   echo teststring >> /tmp/testfile
  （Do the echo operation while C program sleeping）
4. On Client :
   See the C program execute result

Actual Results : read: (NULL)

Expected Results : read: teststring

Additional info :
I have investigated the problem, and found the cause :
In nfsv4 occasions，opening a file with write mode calls the function 
nfs4_proc_file_open(),and nfs4_proc_file_open() will call
nfs_begin_data_update() to declare that a set of operations will update file 
data on the server.
After modifying the file at server side, the Client will call nfs_update_inode
() to update file properties, but nfs_begin_data_update() has been called while 
opening the file, which resulted in nfs_update_inode() to race with
nfs_end_data_update() while updating file properties, so i_size of inode cannot 
be updated correctly (Please refer to nfs_update_inode function).
If the i_size is not updated, nfs_readpages() will not be called for loading 
data at server side while the client is reading files (Please refer to 
__do_page_cache_readahead function)

To resolve this problem, I have made the patch for the kernel.
After the patch is applied, the problem can be resolved.