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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Sun, 26 Apr 2020 13:58:20 -0600
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Subject: Re: INFO: rcu detected stall in wg_packet_tx_worker
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     syzbot <syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        jhs@mojatatu.com,
        =?UTF-8?B?SmnFmcOtIFDDrXJrbw==?= <jiri@resnulli.us>,
        Krzysztof Kozlowski <krzk@kernel.org>, kuba@kernel.org,
        kvalo@codeaurora.org, leon@kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        linux-kselftest@vger.kernel.org, Netdev <netdev@vger.kernel.org>,
        Shuah Khan <shuah@kernel.org>, syzkaller-bugs@googlegroups.com,
        Thomas Gleixner <tglx@linutronix.de>, vivien.didelot@gmail.com,
        Cong Wang <xiyou.wangcong@gmail.com>
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On Sun, Apr 26, 2020 at 1:52 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> It looks like part of the issue might be that I call
> udp_tunnel6_xmit_skb while holding rcu_read_lock_bh, in
> drivers/net/wireguard/socket.c. But I think there's good reason to do
> so, and udp_tunnel6_xmit_skb should be rcu safe. In fact,
> every.single.other user of udp_tunnel6_xmit_skb in the kernel uses it
> with rcu locked. So, hm...

In the syzkaller log, it looks like several runs are hitting:

run #0: crashed: INFO: rcu detected stall in netlink_sendmsg

And other runs are hitting yet different functions. So actually, it's
not clear that this is the fault of the call to udp_tunnel6_xmit_skb.