netdev - Re: unregister_netdevice: waiting for DEV to become free (2)

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Date:   Fri, 15 Nov 2019 18:43:36 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        syzbot <syzbot+30209ea299c09d8785c9@...kaller.appspotmail.com>,
        ddstreet@...e.org, Dmitry Vyukov <dvyukov@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        bpf <bpf@...r.kernel.org>, Yonghong Song <yhs@...com>
Subject: Re: unregister_netdevice: waiting for DEV to become free (2)

Hello.

syzbot is still reporting that bpf(BPF_MAP_UPDATE_ELEM) causes
unregister_netdevice() to hang. It seems that commit 546ac1ffb70d25b5
("bpf: add devmap, a map for storing net device references") assigned
dtab->netdev_map[i] at dev_map_update_elem() but commit 6f9d451ab1a33728
("xdp: Add devmap_hash map type for looking up devices by hashed index")
forgot to assign dtab->netdev_map[idx] at __dev_map_hash_update_elem()
when dev is newly allocated by __dev_map_alloc_node(). As far as I and
syzbot tested, https://syzkaller.appspot.com/x/patch.diff?x=140dd206e00000
can avoid the problem, but I don't know whether this is right location to
assign it. Please check and fix.