NFS: Fix up a race in the NFS implementation of GETLK

 ...and fix a memory corruption bug due to improper use of memcpy() on
 a struct file_lock.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/file.c

@@ -376,22 +376,31 @@ out_swapfile:
 
 static int do_getlk(struct file *filp, int cmd, struct file_lock *fl)
 {
+	struct file_lock *cfl;
 	struct inode *inode = filp->f_mapping->host;
 	int status = 0;
 
 	lock_kernel();
-	/* Use local locking if mounted with "-onolock" */
-	if (!(NFS_SERVER(inode)->flags & NFS_MOUNT_NONLM))
-		status = NFS_PROTO(inode)->lock(filp, cmd, fl);
-	else {
-		struct file_lock *cfl = posix_test_lock(filp, fl);
-
-		fl->fl_type = F_UNLCK;
-		if (cfl != NULL)
-			memcpy(fl, cfl, sizeof(*fl));
+	/* Try local locking first */
+	cfl = posix_test_lock(filp, fl);
+	if (cfl != NULL) {
+		locks_copy_lock(fl, cfl);
+		goto out;
 	}
+
+	if (nfs_have_delegation(inode, FMODE_READ))
+		goto out_noconflict;
+
+	if (NFS_SERVER(inode)->flags & NFS_MOUNT_NONLM)
+		goto out_noconflict;
+
+	status = NFS_PROTO(inode)->lock(filp, cmd, fl);
+out:
 	unlock_kernel();
 	return status;
+out_noconflict:
+	fl->fl_type = F_UNLCK;
+	goto out;
 }
 
 static int do_vfs_lock(struct file *file, struct file_lock *fl)