Messages in this thread | | | Subject | Re: WARNING in __mmdrop | From | Jason Wang <> | Date | Tue, 23 Jul 2019 13:48:52 +0800 |
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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
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