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 <michal.swiatkowski@linux.intel.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20250110004505.3210140-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index a3bdaf075b6b95d16da0ff4ad0d625d370b8c985..c59619a2ec236e5a9a55f86ef2170fd00c896b53 100644 (file)
--- 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;