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Subject: Re: INFO: rcu detected stall in wg_packet_tx_worker
To:     syzbot <syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com>,
        Jason@zx2c4.com, davem@davemloft.net, f.fainelli@gmail.com,
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        leon@kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, netdev@vger.kernel.org,
        shuah@kernel.org, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de, vivien.didelot@gmail.com,
        xiyou.wangcong@gmail.com
References: <0000000000005fd19505a4355311@google.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <e40c443e-74aa-bad4-7be8-4cdddfdf3eaf@gmail.com>
Date:   Sun, 26 Apr 2020 12:40:47 -0700
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On 4/26/20 10:57 AM, syzbot wrote:
> syzbot has bisected this bug to:
> 
> commit e7096c131e5161fa3b8e52a650d7719d2857adfd
> Author: Jason A. Donenfeld <Jason@zx2c4.com>
> Date:   Sun Dec 8 23:27:34 2019 +0000
> 
>     net: WireGuard secure network tunnel
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15258fcfe00000
> start commit:   b2768df2 Merge branch 'for-linus' of git://git.kernel.org/..
> git tree:       upstream
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=17258fcfe00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13258fcfe00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b7a70e992f2f9b68
> dashboard link: https://syzkaller.appspot.com/bug?extid=0251e883fe39e7a0cb0a
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15f5f47fe00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11e8efb4100000
> 
> Reported-by: syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com
> Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 

I have not looked at the repro closely, but WireGuard has some workers
that might loop forever, cond_resched() might help a bit.

diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
index da3b782ab7d31df11e381529b144bcc494234a38..349a71e1907e081c61967c77c9f25a6ec5e57a24 100644
--- a/drivers/net/wireguard/receive.c
+++ b/drivers/net/wireguard/receive.c
@@ -518,6 +518,7 @@ void wg_packet_decrypt_worker(struct work_struct *work)
                                &PACKET_CB(skb)->keypair->receiving)) ?
                                PACKET_STATE_CRYPTED : PACKET_STATE_DEAD;
                wg_queue_enqueue_per_peer_napi(skb, state);
+               cond_resched();
        }
 }
 
diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c
index 7348c10cbae3db54bfcb31f23c2753185735f876..f5b88693176c84b4bfdf8c4e05071481a3ce45b5 100644
--- a/drivers/net/wireguard/send.c
+++ b/drivers/net/wireguard/send.c
@@ -281,6 +281,7 @@ void wg_packet_tx_worker(struct work_struct *work)
 
                wg_noise_keypair_put(keypair, false);
                wg_peer_put(peer);
+               cond_resched();
        }
 }