From 2d36ec73836e83175deb467fd494c61006107e5d Mon Sep 17 00:00:00 2001 From: Yun Zhou Date: Thu, 8 Oct 2026 17:38:24 +0800 Subject: [PATCH] net: erspan: set lltx to avoid sch_direct_xmit deadlock The ERSPAN xmit path re-enters the network stack, causing nested acquisition of _xmit_lock on the underlay device while already holding the ERSPAN device's _xmit_lock, creating an ABBA deadlock. This happens for both IPv4 ERSPAN (erspan_xmit() -> ip_tunnel_xmit()) and IPv6 ERSPAN (ip6erspan_tunnel_xmit() -> ip6_tnl_xmit()): sch_direct_xmit [lock erspan] -> erspan_xmit -> ip_tunnel_xmit -> ip_output -> __dev_queue_xmit -> sch_direct_xmit [lock underlay] sch_direct_xmit [lock erspan] -> ip6erspan_tunnel_xmit -> ip6_tnl_xmit -> ip6_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 the ERSPAN xmit path has no shared mutable state: o_seqno is atomic, TX stats are per-CPU u64_stats, dst_cache is per-CPU, and o_flags is no longer modified in the xmit path since commit 9958e69b9893 ("gre: fix ERSPAN o_flags race/corruption in xmit and fill_info"). GRETAP, the sibling device with identical xmit structure, already sets lltx. Reported-by: syzbot+9bda1b9fbb7fbdf9b62b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9bda1b9fbb7fbdf9b62b Fixes: 84e54fe0a5ea ("gre: introduce native tunnel support for ERSPAN") Fixes: 5a963eb61b7c ("ip6_gre: Add ERSPAN native tunnel support") Cc: stable@vger.kernel.org # 9958e69b9893 ("gre: fix ERSPAN o_flags race/corruption in xmit and fill_info") Cc: stable@vger.kernel.org Signed-off-by: Yun Zhou Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20261008093824.119453-1-yun.zhou@windriver.com Signed-off-by: Jakub Kicinski --- net/ipv4/ip_gre.c | 1 + net/ipv6/ip6_gre.c | 1 + 2 files changed, 2 insertions(+) diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index e4878e9aa636..149a4e83b692 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -1367,6 +1367,7 @@ 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; + dev->lltx = true; netif_keep_dst(dev); return ip_tunnel_init(dev); diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index 04f7c70b7320..3429543ec77e 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -1864,6 +1864,7 @@ static int ip6erspan_tap_init(struct net_device *dev) dev->mtu -= 8; dev->priv_flags |= IFF_LIVE_ADDR_CHANGE; + dev->lltx = true; ip6erspan_tnl_link_config(tunnel, 1); netdev_hold(dev, &tunnel->dev_tracker, GFP_KERNEL);