netdev - [PATCH v3 net-next 10/15] neighbour: Drop read_lock_bh(&tbl->lock) in pneigh_dump

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Message-ID: <20250716221221.442239-11-kuniyu@google.com>
Date: Wed, 16 Jul 2025 22:08:15 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: [PATCH v3 net-next 10/15] neighbour: Drop read_lock_bh(&tbl->lock) in pneigh_dump_table().

Now pneigh_entry is guaranteed to be alive during the
RCU critical section even without holding tbl->lock.

Let's drop read_lock_bh(&tbl->lock) and use rcu_dereference()
to iterate tbl->phash_buckets[] in pneigh_dump_table()

Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
 net/core/neighbour.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 017f41792332b..c7e0611219710 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2808,14 +2808,12 @@ static int pneigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
 	if (filter->dev_idx || filter->master_idx)
 		flags |= NLM_F_DUMP_FILTERED;
 
-	read_lock_bh(&tbl->lock);
-
 	for (h = s_h; h <= PNEIGH_HASHMASK; h++) {
 		if (h > s_h)
 			s_idx = 0;
-		for (n = rcu_dereference_protected(tbl->phash_buckets[h], 1), idx = 0;
+		for (n = rcu_dereference(tbl->phash_buckets[h]), idx = 0;
 		     n;
-		     n = rcu_dereference_protected(n->next, 1)) {
+		     n = rcu_dereference(n->next)) {
 			if (idx < s_idx || pneigh_net(n) != net)
 				goto next;
 			if (neigh_ifindex_filtered(n->dev, filter->dev_idx) ||
@@ -2824,16 +2822,13 @@ static int pneigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
 			err = pneigh_fill_info(skb, n, NETLINK_CB(cb->skb).portid,
 					       cb->nlh->nlmsg_seq,
 					       RTM_NEWNEIGH, flags, tbl);
-			if (err < 0) {
-				read_unlock_bh(&tbl->lock);
+			if (err < 0)
 				goto out;
-			}
 		next:
 			idx++;
 		}
 	}
 
-	read_unlock_bh(&tbl->lock);
 out:
 	cb->args[3] = h;
 	cb->args[4] = idx;
-- 
2.50.0.727.gbf7dc18ff4-goog