netdev - [PATCH net-next 1/8] net: core: neighbour: Add a neigh_fill

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Message-ID: <accfea32900e3f117e684ac2e6ceecd273bd843b.1768225160.git.petrm@nvidia.com>
Date: Wed, 14 Jan 2026 10:54:44 +0100
From: Petr Machata <petrm@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	<netdev@...r.kernel.org>
CC: Ido Schimmel <idosch@...dia.com>, Kuniyuki Iwashima <kuniyu@...gle.com>,
	Breno Leitao <leitao@...ian.org>, Andy Roulin <aroulin@...dia.com>,
	"Francesco Ruggeri" <fruggeri@...sta.com>, Stephen Hemminger
	<stephen@...workplumber.org>, Petr Machata <petrm@...dia.com>,
	<mlxsw@...dia.com>
Subject: [PATCH net-next 1/8] net: core: neighbour: Add a neigh_fill_info() helper for when lock not held

The netlink message needs to be formatted and sent inside the critical
section where the neighbor is changed, so that it reflects the
notified-upon neighbor state. Because it will happen inside an already
existing critical section, it has to assume that the neighbor lock is held.
Add a helper __neigh_fill_info(), which is like neigh_fill_info(), but
makes this assumption. Convert neigh_fill_info() to a wrapper around this
new helper.

Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/core/neighbour.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 96a3b1a93252..6cdd93dfa3ea 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2622,8 +2622,8 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len;
 }
 
-static int neigh_fill_info(struct sk_buff *skb, struct neighbour *neigh,
-			   u32 pid, u32 seq, int type, unsigned int flags)
+static int __neigh_fill_info(struct sk_buff *skb, struct neighbour *neigh,
+			     u32 pid, u32 seq, int type, unsigned int flags)
 {
 	u32 neigh_flags, neigh_flags_ext;
 	unsigned long now = jiffies;
@@ -2649,23 +2649,19 @@ static int neigh_fill_info(struct sk_buff *skb, struct neighbour *neigh,
 	if (nla_put(skb, NDA_DST, neigh->tbl->key_len, neigh->primary_key))
 		goto nla_put_failure;
 
-	read_lock_bh(&neigh->lock);
 	ndm->ndm_state	 = neigh->nud_state;
 	if (neigh->nud_state & NUD_VALID) {
 		char haddr[MAX_ADDR_LEN];
 
 		neigh_ha_snapshot(haddr, neigh, neigh->dev);
-		if (nla_put(skb, NDA_LLADDR, neigh->dev->addr_len, haddr) < 0) {
-			read_unlock_bh(&neigh->lock);
+		if (nla_put(skb, NDA_LLADDR, neigh->dev->addr_len, haddr) < 0)
 			goto nla_put_failure;
-		}
 	}
 
 	ci.ndm_used	 = jiffies_to_clock_t(now - neigh->used);
 	ci.ndm_confirmed = jiffies_to_clock_t(now - neigh->confirmed);
 	ci.ndm_updated	 = jiffies_to_clock_t(now - neigh->updated);
 	ci.ndm_refcnt	 = refcount_read(&neigh->refcnt) - 1;
-	read_unlock_bh(&neigh->lock);
 
 	if (nla_put_u32(skb, NDA_PROBES, atomic_read(&neigh->probes)) ||
 	    nla_put(skb, NDA_CACHEINFO, sizeof(ci), &ci))
@@ -2684,6 +2680,20 @@ static int neigh_fill_info(struct sk_buff *skb, struct neighbour *neigh,
 	return -EMSGSIZE;
 }
 
+static int neigh_fill_info(struct sk_buff *skb, struct neighbour *neigh,
+			   u32 pid, u32 seq, int type, unsigned int flags)
+	__releases(neigh->lock)
+	__acquires(neigh->lock)
+{
+	int err;
+
+	read_lock_bh(&neigh->lock);
+	err = __neigh_fill_info(skb, neigh, pid, seq, type, flags);
+	read_unlock_bh(&neigh->lock);
+
+	return err;
+}
+
 static int pneigh_fill_info(struct sk_buff *skb, struct pneigh_entry *pn,
 			    u32 pid, u32 seq, int type, unsigned int flags,
 			    struct neigh_table *tbl)
-- 
2.51.1