convert pstore

object creation by d_alloc_name()+d_add() in pstore_mkfile(), removal -
via normal VFS codepaths (with ->unlink() using simple_unlink()) or
in pstore_put_backend_records() via locked_recursive_removal()

Replace d_add() with d_make_persistent()+dput() - that's what really
happens there. The reference that goes into record->dentry is valid
only until the unlink (and explicitly cleared by pstore_unlink()).

Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/pstore/inode.c

···
 	if (!dentry)
 		return -ENOMEM;
 
-	private->dentry = dentry;
+	private->dentry = dentry; // borrowed
 	private->record = record;
 	inode->i_size = private->total_size = size;
 	inode->i_private = private;
···
 		inode_set_mtime_to_ts(inode,
 				      inode_set_ctime_to_ts(inode, record->time));
 
-	d_add(dentry, no_free_ptr(inode));
+	d_make_persistent(dentry, no_free_ptr(inode));
+	dput(dentry);
 
 	list_add(&(no_free_ptr(private))->list, &records_list);
 
···
 	guard(mutex)(&pstore_sb_lock);
 	WARN_ON(pstore_sb && pstore_sb != sb);
 
-	kill_litter_super(sb);
+	kill_anon_super(sb);
 	pstore_sb = NULL;
 
 	guard(mutex)(&records_list_lock);