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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E1186ECDE5F for ; Sat, 21 Jul 2018 07:53:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9252A20849 for ; Sat, 21 Jul 2018 07:53:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9252A20849 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.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 S1727486AbeGUIpn (ORCPT ); Sat, 21 Jul 2018 04:45:43 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:48704 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727041AbeGUIpm (ORCPT ); Sat, 21 Jul 2018 04:45:42 -0400 Received: from localhost (LFbn-1-12238-233.w90-92.abo.wanadoo.fr [90.92.53.233]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id E8F8EAE7; Sat, 21 Jul 2018 07:53:52 +0000 (UTC) Date: Sat, 21 Jul 2018 09:53:50 +0200 From: Greg Kroah-Hartman To: Benjamin Herrenschmidt Cc: Linus Torvalds , "Eric W. Biederman" , Joel Stanley , Linux Kernel Mailing List Subject: Re: [PATCH 1/2] drivers: core: Don't try to use a dead glue_dir Message-ID: <20180721075350.GA17840@kroah.com> References: <828fb935c0cd04e74a09b8ed2b78aca405d7c5b2.camel@kernel.crashing.org> <20180707164838.GC16279@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 10, 2018 at 09:44:33AM +1000, Benjamin Herrenschmidt wrote: > 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). To follow up on this. I've applied the 2/2 patch for this series, so this 1/2 "should" not be needed. Ben, if you still see this trigger with that, I guess I can take this, but it still feels wrong to me :) thanks, greg k-h