[CIFS] lseek polling returned stale EOF

Fixes Samba bug 4362

Discovered by Jeremy Allison

Clipper database polls on EOF via lseek and can get stale EOF
when file is open on different client

Signed-off-by: Jeremy Allison <jra@samba.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsfs.c

@@ -511,7 +511,15 @@ static loff_t cifs_llseek(struct file *file, loff_t offset, int origin)
 {
 	/* origin == SEEK_END => we must revalidate the cached file length */
 	if (origin == SEEK_END) {
-		int retval = cifs_revalidate(file->f_path.dentry);
+		int retval;
+
+		/* some applications poll for the file length in this strange
+		   way so we must seek to end on non-oplocked files by
+		   setting the revalidate time to zero */
+		if(file->f_path.dentry->d_inode)		
+			CIFS_I(file->f_path.dentry->d_inode)->time = 0;
+
+		retval = cifs_revalidate(file->f_path.dentry);
 		if (retval < 0)
 			return (loff_t)retval;
 	}