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Date:   Sun, 26 Apr 2020 13:58:20 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     syzbot <syzbot+0251e883fe39e7a0cb0a@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        jhs@...atatu.com,
        Jiří Pírko <jiri@...nulli.us>,
        Krzysztof Kozlowski <krzk@...nel.org>, kuba@...nel.org,
        kvalo@...eaurora.org, leon@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>, syzkaller-bugs@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>, vivien.didelot@...il.com,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: INFO: rcu detected stall in wg_packet_tx_worker

On Sun, Apr 26, 2020 at 1:52 PM Jason A. Donenfeld <Jason@...c4.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.

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