net: warn during dump if NAPI list is not sorted

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.

Reviewed-by: Michal Swiatkowski <[email protected]>
Reviewed-by: Joe Damato <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

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;