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_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 B1F63C7618B for ; Tue, 23 Jul 2019 13:37:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B84E218D4 for ; Tue, 23 Jul 2019 13:37:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390306AbfGWNht (ORCPT ); Tue, 23 Jul 2019 09:37:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51142 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729782AbfGWNhs (ORCPT ); Tue, 23 Jul 2019 09:37:48 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4B9B230C34D1; Tue, 23 Jul 2019 13:37:48 +0000 (UTC) Received: from [10.72.12.26] (ovpn-12-26.pek2.redhat.com [10.72.12.26]) by smtp.corp.redhat.com (Postfix) with ESMTP id D55375D9C5; Tue, 23 Jul 2019 13:37:18 +0000 (UTC) Subject: Re: WARNING in __mmdrop To: "Michael S. Tsirkin" Cc: syzbot , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org References: <0000000000008dd6bb058e006938@google.com> <000000000000964b0d058e1a0483@google.com> <20190721044615-mutt-send-email-mst@kernel.org> <75c43998-3a1c-676f-99ff-3d04663c3fcc@redhat.com> <20190722035657-mutt-send-email-mst@kernel.org> <20190723010156-mutt-send-email-mst@kernel.org> <124be1a2-1c53-8e65-0f06-ee2294710822@redhat.com> <20190723032800-mutt-send-email-mst@kernel.org> <20190723062842-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <025aa12a-c789-7eac-ba96-48e4dd3dd551@redhat.com> Date: Tue, 23 Jul 2019 21:37:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190723062842-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Tue, 23 Jul 2019 13:37:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/7/23 下午6:42, Michael S. Tsirkin wrote: > On Tue, Jul 23, 2019 at 04:42:19PM +0800, Jason Wang wrote: >>> So how about this: do exactly what you propose but as a 2 patch series: >>> start with the slow safe patch, and add then return uaddr optimizations >>> on top. We can then more easily reason about whether they are safe. >> >> If you stick, I can do this. > So I definitely don't insist but I'd like us to get back to where > we know existing code is very safe (if not super fast) and > optimizing from there. Bugs happen but I'd like to see a bisect > giving us "oh it's because of XYZ optimization" and not the > general "it's somewhere within this driver" that we are getting > now. Syzbot has bisected to the commit of metadata acceleration in fact :) > > Maybe the way to do this is to revert for this release cycle > and target the next one. What do you think? I would try to fix the issues consider packed virtqueue which may use this for a good performance number. But if you insist, I'm ok to revert. Or maybe introduce a config option to disable it by default (almost all optimized could be ruled out). Thanks