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Subject: Re: unregister_netdevice: waiting for DEV to become free (2)
To:     =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= <toke@redhat.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        syzbot <syzbot+30209ea299c09d8785c9@syzkaller.appspotmail.com>,
        ddstreet@ieee.org, Dmitry Vyukov <dvyukov@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        bpf <bpf@vger.kernel.org>, Yonghong Song <yhs@fb.com>
References: <00000000000056268e05737dcb95@google.com>
 <0000000000007d22100573d66078@google.com>
 <063a57ba-7723-6513-043e-ee99c5797271@I-love.SAKURA.ne.jp>
 <CAADnVQJ7BZMVSt9on4updWrWsFWq6b5J1qEGwTdGYV+BLqH7tg@mail.gmail.com>
 <87imopgere.fsf@toke.dk>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Message-ID: <6f69f704-b51d-c3cb-02c6-8e6eb93f4194@i-love.sakura.ne.jp>
Date:   Fri, 15 Nov 2019 18:43:36 +0900
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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.