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[209.132.183.28]) by mx.google.com with ESMTPS id e12si24391972qve.144.2019.07.22.01.02.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 Jul 2019 01:02:25 -0700 (PDT) Received-SPF: pass (google.com: domain of mst@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 mst@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 269F7308424C; Mon, 22 Jul 2019 08:02:24 +0000 (UTC) Received: from redhat.com (ovpn-120-233.rdu2.redhat.com [10.10.120.233]) by smtp.corp.redhat.com (Postfix) with ESMTP id D54DC610A6; Mon, 22 Jul 2019 08:02:14 +0000 (UTC) Date: Mon, 22 Jul 2019 04:02:13 -0400 From: "Michael S. Tsirkin" To: Jason Wang 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 Subject: Re: WARNING in __mmdrop Message-ID: <20190722035657-mutt-send-email-mst@kernel.org> References: <0000000000008dd6bb058e006938@google.com> <000000000000964b0d058e1a0483@google.com> <20190721044615-mutt-send-email-mst@kernel.org> <75c43998-3a1c-676f-99ff-3d04663c3fcc@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <75c43998-3a1c-676f-99ff-3d04663c3fcc@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Mon, 22 Jul 2019 08:02:24 +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 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? 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. -- MST