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net: dst: introduce dst->dev_rcu

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Followup of commit 88fe14253e ("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: 4a6ce2b6f2 ("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>
This commit is contained in:
Eric Dumazet
2025-08-28 19:58:16 +00:00
committed by Jakub Kicinski
parent e71aa5a955
commit caedcc5b6d
3 changed files with 14 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
include/net/dst.h
View File

@@ -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);

2
net/core/dst.c
View File

@@ -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);
}

4
net/ipv4/route.c
View File

@@ -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();