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Date:   Thu, 25 Jul 2019 02:02:41 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     syzbot <syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com>,
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        elena.reshetova@intel.com, guro@fb.com, hch@infradead.org,
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        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: <20190725015402-mutt-send-email-mst@kernel.org>
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On Mon, Jul 22, 2019 at 11:11:52AM -0300, Jason Gunthorpe wrote:
> On Sun, Jul 21, 2019 at 06:02:52AM -0400, 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 <jasowang@redhat.com>
> > > 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:
> 
> This stuff looks quite similar to the hmm_mirror use model and other
> places in the kernel. I'm still hoping we can share this code a bit more.

Right. I think hmm is something we should look at.

-- 
MST