Subject: [PATCH net-next] net: warn during dump if NAPI list is not sorted

From: Jakub Kicinski <[email-masked]>
Date: Thu, 9 Jan 2025 16:45:04 -0800

Dump continuation depends on the NAPI list being sorted.
Broken netlink dump continuation may be rare and hard to debug
so add a warning if we notice the potential problem while walking
the list.

Signed-off-by: Jakub Kicinski <[email-masked]>
---
This is really a follow up to commit d6c7b03497ee ("net: make sure
we retain NAPI ordering on netdev->napi_list") but I had to wait
for some fixes to make it to net-next.

CC: [email-masked]
CC: [email-masked]
---
 net/core/netdev-genl.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index a3bdaf075b6b..c59619a2ec23 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -263,14 +263,21 @@ netdev_nl_napi_dump_one(struct net_device *netdev, struct sk_buff *rsp,
 			struct netdev_nl_dump_ctx *ctx)
 {
 	struct napi_struct *napi;
+	unsigned int prev_id;
 	int err = 0;
 
 	if (!(netdev->flags & IFF_UP))
 		return err;
 
+	prev_id = UINT_MAX;
 	list_for_each_entry(napi, &netdev->napi_list, dev_list) {
 		if (napi->napi_id < MIN_NAPI_ID)
 			continue;
+
+		/* Dump continuation below depends on the list being sorted */
+		WARN_ON_ONCE(napi->napi_id >= prev_id);
+		prev_id = napi->napi_id;
+
 		if (ctx->napi_id && napi->napi_id >= ctx->napi_id)
 			continue;
 
-- 
2.47.1