From: Your Name erspan_xmit() re-enters the network stack via ip_tunnel_xmit(), causing nested acquisition of _xmit_lock on the underlay device while already holding the ERSPAN device's _xmit_lock. Both are ARPHRD_ETHER and share the same lockdep class, creating an ABBA deadlock: sch_direct_xmit [lock erspan] -> erspan_xmit -> ip_tunnel_xmit -> ip_output -> __dev_queue_xmit -> sch_direct_xmit [lock underlay] Set dev->lltx = true so HARD_TX_LOCK() skips the spinlock for ERSPAN. This is safe as erspan_xmit() has no shared mutable state: o_seqno is atomic, stats use atomic_long_inc, and dst_cache is per-CPU. GRETAP, the sibling device with identical xmit structure, already sets lltx. Closes: https://syzkaller.appspot.com/bug?extid=9bda1b9fbb7fbdf9b62b Reported-by: syzbot+9bda1b9fbb7fbdf9b62b@syzkaller.appspotmail.com Fixes: 84e54fe0a5ea ("gre: introduce native tunnel support for ERSPAN") Signed-off-by: Yun Zhou --- net/ipv4/ip_gre.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index 3efdfb4ffa21..9fbff16cda1d 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -1363,6 +1363,8 @@ static int erspan_tunnel_init(struct net_device *dev) dev->features |= GRE_FEATURES; dev->hw_features |= GRE_FEATURES; dev->priv_flags |= IFF_LIVE_ADDR_CHANGE; + /* Skip TX lock: xmit re-enters stack, risking ABBA with underlay */ + dev->lltx = true; netif_keep_dst(dev); return ip_tunnel_init(dev); -- 2.43.0