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[209.132.183.28]) by mx.google.com with ESMTPS id z57si24698218qta.330.2019.07.23.06.37.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jul 2019 06:37:49 -0700 (PDT) Received-SPF: pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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