Revert "debugfs: inode: debugfs_create_dir uses mode permission from parent"

This reverts commit 95cde3c.

The commit had good intentions, but it breaks kvm-tool and qemu-kvm.

With it in place, "lkvm run" just fails with

  Error: KVM_CREATE_VM ioctl
  Warning: Failed init: kvm__init

which isn't a wonderful error message, but bisection pinpointed the
problematic commit.

The problem is almost certainly due to the special kvm debugfs entries
created dynamically by kvm under /sys/kernel/debug/kvm/.  See
kvm_create_vm_debugfs()

Bisected-and-reported-by: Linus Torvalds <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Thomas Richter <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: torvalds

fs/debugfs/inode.c

@@ -512,9 +512,7 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
 	if (unlikely(!inode))
 		return failed_creating(dentry);
 
-	if (!parent)
-		parent = debugfs_mount->mnt_root;
-	inode->i_mode = S_IFDIR | ((d_inode(parent)->i_mode & 0770));
+	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
 	inode->i_op = &simple_dir_inode_operations;
 	inode->i_fop = &simple_dir_operations;