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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable 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 1DF9BC10F05 for ; Wed, 20 Mar 2019 15:12:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E37C121873 for ; Wed, 20 Mar 2019 15:12:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553094756; bh=cgey03YGMsaWzYa5SArv5hvqi4kZuGNAoXv+ly7VTmE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=XUf58BQ2sc5Je4qGHUl82QaYCRwlqlp7zkb8HMWrtHGG3pWNGCLOB9i8yi/7e4/zQ DgdgTXe7tYfdeYqycwC89n/Utv/Q79V7rUGtLvPqJhVwZdGuKo1S1AsiS/Vsn3mQC/ vkSqJ6onU2oxFBXIis9VQpLvSlTN0VTknMcaS9p0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727379AbfCTPMf (ORCPT ); Wed, 20 Mar 2019 11:12:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:37312 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726169AbfCTPMe (ORCPT ); Wed, 20 Mar 2019 11:12:34 -0400 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D12AC2184D; Wed, 20 Mar 2019 15:12:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553094754; bh=cgey03YGMsaWzYa5SArv5hvqi4kZuGNAoXv+ly7VTmE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=f3IPKlYueZ3ybYTH2vqMBuXDNfzG6zUlG70z3mLEZGAWs0QThz2omqqFsUwk3SUwO wM1RFoiXQU4vYmF7ts1KzBZAvPXqYkclQCkFG5ytbspifRrv2/6MjSxzIAI68nlxJr 5HsRuIvw1710NN1z5K+o678b10EImgBdslbufVFM= Date: Wed, 20 Mar 2019 16:12:31 +0100 From: Greg KH To: Jan Kara Cc: stable@vger.kernel.org, Jens Axboe , linux-block@vger.kernel.org Subject: Re: Revert commit 310ca162d77 Message-ID: <20190320151231.GA31247@kroah.com> References: <20190320125806.GD9485@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190320125806.GD9485@quack2.suse.cz> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Mar 20, 2019 at 01:58:06PM +0100, Jan Kara wrote: > Hello, > > commit 310ca162d77 "block/loop: Use global lock for ioctl() operation." has > been pushed to multiple stable trees. This patch is a part of larger series > that overhauls the locking inside loopback device upstream and for 4.4, > 4.9, and 4.14 stable trees only this patch from the series is applied. Our > testing now has shown [1] that the patch alone makes present deadlocks > inside loopback driver more likely (the openqa test in our infrastructure > didn't hit the deadlock before whereas with the new kernel it hits it > reliably every time). So I would suggest we revert 310ca162d77 from 4.4, > 4.9, and 4.14 kernels. Ugh, ok. > Another option would be to backport other locking fixes for the loop > device but honestly I don't think that's a stable material - never heard > of real users hitting problems, only syzkaller could, and we are still > fixing up some small glitches resulting from that rework... I tried to backport a number of the loop fixes, and odds are I am the one that grabbed this. There are other loop locking fixes in the stable releases, I don't know if I can just revert this one, let me check... And yes, I did get some loop bugreports from the Android kernel team as they are using loop devices in large numbers on the new Android release for something. So I think they have already backported a number of these fixes to their trees, which made me want to push these out to more people. Also, given that syzbot has a reproducer for 310ca162d77, are we worst off if we revert it? thanks, greg k-h