From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D549C5CFE7 for ; Mon, 9 Jul 2018 23:44:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 728CF208A2 for ; Mon, 9 Jul 2018 23:44:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 728CF208A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933375AbeGIXow (ORCPT ); Mon, 9 Jul 2018 19:44:52 -0400 Received: from gate.crashing.org ([63.228.1.57]:58096 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932847AbeGIXou (ORCPT ); Mon, 9 Jul 2018 19:44:50 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id w69NiXMK024595; Mon, 9 Jul 2018 18:44:34 -0500 Message-ID: Subject: Re: [PATCH 1/2] drivers: core: Don't try to use a dead glue_dir From: Benjamin Herrenschmidt To: Greg Kroah-Hartman , Linus Torvalds Cc: "Eric W. Biederman" , Joel Stanley , Linux Kernel Mailing List Date: Tue, 10 Jul 2018 09:44:33 +1000 In-Reply-To: <20180707164838.GC16279@kroah.com> References: <828fb935c0cd04e74a09b8ed2b78aca405d7c5b2.camel@kernel.crashing.org> <20180707164838.GC16279@kroah.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.3 (3.28.3-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2018-07-07 at 18:48 +0200, Greg Kroah-Hartman wrote: > No, kobject_get() should never happen on a 0 refcount object. That > being said, the code does allow it, so if things are messed up, it will > happen. I think that change happened when the switch to refcount_t > occured, before then we would WARN_ON() if that ever happened. I should > go fix that up, and restore that old behavior, so that syzbot starts > complaining loudly when stuff like that hits. > > So I hate using kobject_get_unless_zero(), and resisted ever adding it > to the tree as it shows a bad locking/tree situation as you point out > here. But for some reason, the block developers seemed to insist they > needed it, and so it is in the tree for them. I don't want it to spread > if at all possible, which makes me want to reject this patch as this > should be "a case that can never be hit". Except it can in that situation... at least unless you get my patch 2/2 (or the newer one I'm about to send that avoids adding a child counter and uses the one in kernfs instead). Ben.