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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Sun, 26 Apr 2020 13:52:45 -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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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...