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[209.132.183.28]) by mx.google.com with ESMTPS id c191si25820829qkb.4.2019.07.23.00.55.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jul 2019 00:56:00 -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-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CA944859FF; Tue, 23 Jul 2019 07:55:58 +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 AD23F60603; Tue, 23 Jul 2019 07:55:46 +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> <20190723032346-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <9a9a7ac0-2657-ff09-2644-f8d7ae0f9222@redhat.com> Date: Tue, 23 Jul 2019 15:55:47 +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: <20190723032346-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 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 23 Jul 2019 07:55:59 +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3:25, Michael S. Tsirkin wrote: > On Tue, Jul 23, 2019 at 01:48:52PM +0800, Jason Wang wrote: >> On 2019/7/23 下午1:02, Michael S. Tsirkin wrote: >>> On Tue, Jul 23, 2019 at 11:55:28AM +0800, Jason Wang wrote: >>>> On 2019/7/22 下午4:02, Michael S. Tsirkin wrote: >>>>> On Mon, Jul 22, 2019 at 01:21:59PM +0800, Jason Wang wrote: >>>>>> On 2019/7/21 下午6:02, Michael S. Tsirkin wrote: >>>>>>> On Sat, Jul 20, 2019 at 03:08:00AM -0700, syzbot wrote: >>>>>>>> syzbot has bisected this bug to: >>>>>>>> >>>>>>>> commit 7f466032dc9e5a61217f22ea34b2df932786bbfc >>>>>>>> Author: Jason Wang >>>>>>>> Date: Fri May 24 08:12:18 2019 +0000 >>>>>>>> >>>>>>>> vhost: access vq metadata through kernel virtual address >>>>>>>> >>>>>>>> bisection log:https://syzkaller.appspot.com/x/bisect.txt?x=149a8a20600000 >>>>>>>> start commit: 6d21a41b Add linux-next specific files for 20190718 >>>>>>>> git tree: linux-next >>>>>>>> final crash:https://syzkaller.appspot.com/x/report.txt?x=169a8a20600000 >>>>>>>> console output:https://syzkaller.appspot.com/x/log.txt?x=129a8a20600000 >>>>>>>> kernel config:https://syzkaller.appspot.com/x/.config?x=3430a151e1452331 >>>>>>>> dashboard link:https://syzkaller.appspot.com/bug?extid=e58112d71f77113ddb7b >>>>>>>> syz repro:https://syzkaller.appspot.com/x/repro.syz?x=10139e68600000 >>>>>>>> >>>>>>>> Reported-by:syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com >>>>>>>> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual >>>>>>>> address") >>>>>>>> >>>>>>>> For information about bisection process see:https://goo.gl/tpsmEJ#bisection >>>>>>> OK I poked at this for a bit, I see several things that >>>>>>> we need to fix, though I'm not yet sure it's the reason for >>>>>>> the failures: >>>>>>> >>>>>>> >>>>>>> 1. mmu_notifier_register shouldn't be called from vhost_vring_set_num_addr >>>>>>> That's just a bad hack, >>>>>> This is used to avoid holding lock when checking whether the addresses are >>>>>> overlapped. Otherwise we need to take spinlock for each invalidation request >>>>>> even if it was the va range that is not interested for us. This will be very >>>>>> slow e.g during guest boot. >>>>> KVM seems to do exactly that. >>>>> I tried and guest does not seem to boot any slower. >>>>> Do you observe any slowdown? >>>> Yes I do. >>>> >>>> >>>>> Now I took a hard look at the uaddr hackery it really makes >>>>> me nervious. So I think for this release we want something >>>>> safe, and optimizations on top. As an alternative revert the >>>>> optimization and try again for next merge window. >>>> Will post a series of fixes, let me know if you're ok with that. >>>> >>>> Thanks >>> I'd prefer you to take a hard look at the patch I posted >>> which makes code cleaner, >> I did. But it looks to me a series that is only about 60 lines of code can >> fix all the issues we found without reverting the uaddr optimization. >> >> >>> and ad optimizations on top. >>> But other ways could be ok too. >> I'm waiting for the test result from syzbot and will post. Let's see if you >> are OK with that. >> >> Thanks > Oh I didn't know one can push a test to syzbot and get back > a result. How does one do that? See here https://github.com/google/syzkaller/blob/master/docs/syzbot.md Just reply this thread by attaching a fix with command like: "#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 7f466032dc9e5a61217f22ea34b2df932786bbfc" Btw, I've let syzbot test you patch, and it passes. Thanks >