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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: syzbot <syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com>,
	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
Date: Tue, 23 Jul 2019 03:25:11 -0400	[thread overview]
Message-ID: <20190723032346-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <124be1a2-1c53-8e65-0f06-ee2294710822@redhat.com>

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 <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:
> > > > > > 
> > > > > > 
> > > > > > 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?


> 
> > > > 

  reply	other threads:[~2019-07-23  7:25 UTC|newest]

Thread overview: 88+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-19  3:35 WARNING in __mmdrop syzbot
2019-07-20 10:08 ` syzbot
2019-07-21 10:02   ` Michael S. Tsirkin
2019-07-21 12:18     ` Michael S. Tsirkin
2019-07-22  5:24       ` Jason Wang
2019-07-22  8:08         ` Michael S. Tsirkin
2019-07-23  4:01           ` Jason Wang
2019-07-23  5:01             ` Michael S. Tsirkin
2019-07-23  5:47               ` Jason Wang
2019-07-23  7:23                 ` Michael S. Tsirkin
2019-07-23  7:53                   ` Jason Wang
2019-07-23  8:10                     ` Michael S. Tsirkin
2019-07-23  8:49                       ` Jason Wang
2019-07-23  9:26                         ` Michael S. Tsirkin
2019-07-23 13:31                           ` Jason Wang
2019-07-25  5:52                             ` Michael S. Tsirkin
2019-07-25  7:43                               ` Jason Wang
2019-07-25  8:28                                 ` Michael S. Tsirkin
2019-07-25 13:21                                   ` Jason Wang
2019-07-25 13:26                                     ` Michael S. Tsirkin
2019-07-25 14:25                                       ` Jason Wang
2019-07-26 11:49                                         ` Michael S. Tsirkin
2019-07-26 12:00                                           ` Jason Wang
2019-07-26 12:38                                             ` Michael S. Tsirkin
2019-07-26 12:53                                               ` Jason Wang
2019-07-26 13:36                                                 ` Jason Wang
2019-07-26 13:49                                                   ` Michael S. Tsirkin
2019-07-29  5:54                                                     ` Jason Wang
2019-07-29  8:59                                                       ` Michael S. Tsirkin
2019-07-29 14:24                                                         ` Jason Wang
2019-07-29 14:44                                                           ` Michael S. Tsirkin
2019-07-30  7:44                                                             ` Jason Wang
2019-07-30  8:03                                                               ` Jason Wang
2019-07-30 15:08                                                               ` Michael S. Tsirkin
2019-07-31  8:49                                                                 ` Jason Wang
2019-07-31 23:00                                                                   ` Jason Gunthorpe
2019-07-26 13:47                                                 ` Michael S. Tsirkin
2019-07-26 14:00                                                   ` Jason Wang
2019-07-26 14:10                                                     ` Michael S. Tsirkin
2019-07-26 15:03                                                     ` Jason Gunthorpe
2019-07-29  5:56                                                       ` Jason Wang
2019-07-21 12:28     ` RFC: call_rcu_outstanding (was Re: WARNING in __mmdrop) Michael S. Tsirkin
2019-07-21 13:17       ` Paul E. McKenney
2019-07-21 17:53         ` Michael S. Tsirkin
2019-07-21 19:28           ` Paul E. McKenney
2019-07-22  7:56             ` Michael S. Tsirkin
2019-07-22 11:57               ` Paul E. McKenney
2019-07-21 21:08         ` Matthew Wilcox
2019-07-21 23:31           ` Paul E. McKenney
2019-07-22  7:52             ` Michael S. Tsirkin
2019-07-22 11:51               ` Paul E. McKenney
2019-07-22 13:41                 ` Jason Gunthorpe
2019-07-22 15:52                   ` Paul E. McKenney
2019-07-22 16:04                     ` Jason Gunthorpe
2019-07-22 16:15                       ` Michael S. Tsirkin
2019-07-22 16:15                       ` Paul E. McKenney
2019-07-22 15:14             ` Joel Fernandes
2019-07-22 15:47               ` Michael S. Tsirkin
2019-07-22 15:55                 ` Paul E. McKenney
2019-07-22 16:13                   ` Michael S. Tsirkin
2019-07-22 16:25                     ` Paul E. McKenney
2019-07-22 16:32                       ` Michael S. Tsirkin
2019-07-22 18:58                         ` Paul E. McKenney
2019-07-22  5:21     ` WARNING in __mmdrop Jason Wang
2019-07-22  8:02       ` Michael S. Tsirkin
2019-07-23  3:55         ` Jason Wang
2019-07-23  5:02           ` Michael S. Tsirkin
2019-07-23  5:48             ` Jason Wang
2019-07-23  7:25               ` Michael S. Tsirkin [this message]
2019-07-23  7:55                 ` Jason Wang
2019-07-23  7:56               ` Michael S. Tsirkin
2019-07-23  8:42                 ` Jason Wang
2019-07-23 10:27                   ` Michael S. Tsirkin
2019-07-23 13:34                     ` Jason Wang
2019-07-23 15:02                       ` Michael S. Tsirkin
2019-07-24  2:17                         ` Jason Wang
2019-07-24  8:05                           ` Michael S. Tsirkin
2019-07-24 10:08                             ` Jason Wang
2019-07-24 18:25                               ` Michael S. Tsirkin
2019-07-25  3:44                                 ` Jason Wang
2019-07-25  5:09                                   ` Michael S. Tsirkin
2019-07-24 16:53                             ` Jason Gunthorpe
2019-07-24 18:25                               ` Michael S. Tsirkin
2019-07-23 10:42                   ` Michael S. Tsirkin
2019-07-23 13:37                     ` Jason Wang
2019-07-22 14:11     ` Jason Gunthorpe
2019-07-25  6:02       ` Michael S. Tsirkin
2019-07-25  7:44         ` Jason Wang

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