Messages in this thread | | | Subject | Re: WARNING in __mmdrop | From | Jason Wang <> | Date | Tue, 23 Jul 2019 15:55:47 +0800 |
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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<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?
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
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