unregister_netdevice: waiting for DEV to become free

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
87ef12027b9b1dd0e0b12cf311fbcb19f9d92539 (Wed Apr 18 19:48:17 2018 +0000)
Merge tag 'ceph-for-4.17-rc2' of git://github.com/ceph/ceph-client
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=2dfb68e639f0621b19fb

So far this crash happened 5 times on upstream.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5531107864870912
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=1808800213120130118
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

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Reported-by: syzbot+2dfb68e639f0621b19fb@xxxxxxxxxxxxxxxxxxxxxxxxx
It will help syzbot understand when the bug is fixed. See footer for  
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connbytes_mt_check: 1 callbacks suppressed
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
unregister_netdevice: waiting for lo to become free. Usage count = 3
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
kernel msg: ebtables bug: please report to author: Entries_size never zero
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
nla_parse: 1 callbacks suppressed
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7
netlink: 17 bytes leftover after parsing attributes in process  
`syz-executor6'.
xt_connbytes: cannot load conntrack support for proto=7


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