Messages in this thread | | | Date | Mon, 20 Aug 2018 15:55:16 +0300 (EEST) | From | Julian Anastasov <> | Subject | Re: unregister_netdevice: waiting for DEV to become free (2) |
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Hello,
On Sun, 19 Aug 2018, syzbot wrote:
> syzbot has found a reproducer for the following crash on: > > HEAD commit: d7857ae43dcc Add linux-next specific files for 20180817 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=13c72fce400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=4b10cd1ea76bb092 > dashboard link: https://syzkaller.appspot.com/bug?extid=30209ea299c09d8785c9 > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=15df679a400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15242741400000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+30209ea299c09d8785c9@syzkaller.appspotmail.com > > IPVS: stopping master sync thread 4657 ... > IPVS: stopping master sync thread 4663 ... > IPVS: sync thread started: state = MASTER, mcast_ifn = syz_tun, syncid = 0, id > IPVS: = 0 > IPVS: sync thread started: state = MASTER, mcast_ifn = syz_tun, syncid = 0, id > IPVS: = 0 > IPVS: stopping master sync thread 4664 ... > unregister_netdevice: waiting for lo to become free. Usage count = 1
Well, only IPVS and tun in the game? But IPVS does not take any dev references for sync threads. Can it be a problem in tun? For example, a side effects from dst_cache_reset? May be dst_release is called too late? Here is what should happen on unregistration:
- NETDEV_UNREGISTER event: rt_flush_dev changes dst->dev with lo but dst is not released
- ndo_uninit/ip_tunnel_uninit: dst_cache_reset is called which does nothing!?! May be dst_release call is needed here.
- no more references are expected here ...
- netdev_run_todo -> netdev_wait_allrefs: loop here due to refcnt!=0
- dev->priv_destructor (ip_tunnel_dev_free) calls dst_cache_destroy where dst_release is used but it is not reached because we loop in netdev_wait_allrefs above
- dst_cache_destroy: really call dst_release
In fact, after calling rt_flush_dev and replacing the dst->dev we should reach dev->priv_destructor (ip_tunnel_dev_free) for tun device where dst_release for lo should be called. But may be something prevents it, exit batching?
Regards
-- Julian Anastasov <ja@ssi.bg>
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