[PATCH v6.1.y 3/4] net: dst: introduce dst->dev_rcu
From: Miguel Gazquez (Schneider Electric) <hidden>
Date: 2026-08-21 13:34:26
Also in:
lkml, netfilter-devel, stable
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
From: Eric Dumazet <edumazet@google.com>
[ Upstream commit caedcc5b6df1b2e2b5f39079e3369c1d4d5c5f50 ]
Followup of commit 88fe14253e18 ("net: dst: add four helpers
to annotate data-races around dst->dev").
We want to gradually add explicit RCU protection to dst->dev,
including lockdep support.
Add an union to alias dst->dev_rcu and dst->dev.
Add dst_dev_net_rcu() helper.
Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250828195823.3958522-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Miguel Gazquez <redacted>
---
include/net/dst.h | 16 +++++++++++-----
net/core/dst.c | 2 +-
net/ipv4/route.c | 4 ++--
3 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index 7c0cf856154d..96dd65a941c5 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h@@ -23,7 +23,10 @@ struct sk_buff; struct dst_entry { - struct net_device *dev; + union { + struct net_device *dev; + struct net_device __rcu *dev_rcu; + }; struct dst_ops *ops; unsigned long _metrics; unsigned long expires;
@@ -562,9 +565,12 @@ static inline struct net_device *dst_dev(const struct dst_entry *dst) static inline struct net_device *dst_dev_rcu(const struct dst_entry *dst) { - /* In the future, use rcu_dereference(dst->dev) */ - WARN_ON_ONCE(!rcu_read_lock_held()); - return READ_ONCE(dst->dev); + return rcu_dereference(dst->dev_rcu); +} + +static inline struct net *dst_dev_net_rcu(const struct dst_entry *dst) +{ + return dev_net_rcu(dst_dev_rcu(dst)); } static inline struct net_device *skb_dst_dev(const struct sk_buff *skb)
@@ -584,7 +590,7 @@ static inline struct net *skb_dst_dev_net(const struct sk_buff *skb) static inline struct net *skb_dst_dev_net_rcu(const struct sk_buff *skb) { - return dev_net_rcu(skb_dst_dev(skb)); + return dev_net_rcu(skb_dst_dev_rcu(skb)); } struct dst_entry *dst_blackhole_check(struct dst_entry *dst, u32 cookie);
diff --git a/net/core/dst.c b/net/core/dst.c
index 24a1cc3d2a08..cbb6888aa32b 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c@@ -151,7 +151,7 @@ void dst_dev_put(struct dst_entry *dst) dst->ops->ifdown(dst, dev, true); dst->input = dst_discard; dst->output = dst_discard_out; - WRITE_ONCE(dst->dev, blackhole_netdev); + rcu_assign_pointer(dst->dev_rcu, blackhole_netdev); netdev_ref_replace(dev, blackhole_netdev, &dst->dev_tracker, GFP_ATOMIC); }
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index a2985265c792..e3cce307e0e9 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c@@ -1069,7 +1069,7 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu) return; rcu_read_lock(); - net = dev_net_rcu(dst_dev(dst)); + net = dst_dev_net_rcu(dst); if (mtu < net->ipv4.ip_rt_min_pmtu) { lock = true; mtu = min(old_mtu, net->ipv4.ip_rt_min_pmtu);
@@ -1367,7 +1367,7 @@ static unsigned int ipv4_default_advmss(const struct dst_entry *dst) struct net *net; rcu_read_lock(); - net = dev_net_rcu(dst_dev(dst)); + net = dst_dev_net_rcu(dst); advmss = max_t(unsigned int, ipv4_mtu(dst) - header_size, net->ipv4.ip_rt_min_advmss); rcu_read_unlock();
--
2.55.0