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Message-ID: <20250828195823.3958522-2-edumazet@google.com>
Date: Thu, 28 Aug 2025 19:58:16 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>,
David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com,
Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/8] net: dst: introduce dst->dev_rcu
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@...gle.com>
---
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 bab01363bb975dc20ea0e1485a515c1872537ab9..f8aa1239b4db639bd6b63f4ddb4ec4d7ee459ac0 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -24,7 +24,10 @@
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;
@@ -570,9 +573,12 @@ 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)
@@ -592,7 +598,7 @@ 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 e2de8b68c41d3fa6f8a94b61b88f531a2d79d3b4..e9d35f49c9e7800d7397b643c70931dd516a6265 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -150,7 +150,7 @@ void dst_dev_put(struct dst_entry *dst)
dst->ops->ifdown(dst, dev);
WRITE_ONCE(dst->input, dst_discard);
WRITE_ONCE(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 771f6986ed05882ebaeb1117ac33d68edf5db699..c63feef55d5193aadd11f9d5b45c8f5482e06be5 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1027,7 +1027,7 @@ 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);
@@ -1327,7 +1327,7 @@ 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();
--
2.51.0.318.gd7df087d1a-goog
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