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

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Message-ID: <20250110004505.3210140-1-kuba@kernel.org>
Date: Thu,  9 Jan 2025 16:45:04 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org,
	edumazet@...gle.com,
	pabeni@...hat.com,
	andrew+netdev@...n.ch,
	horms@...nel.org,
	Jakub Kicinski <kuba@...nel.org>,
	jdamato@...tly.com,
	almasrymina@...gle.com
Subject: [PATCH net-next] 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.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
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: jdamato@...tly.com
CC: almasrymina@...gle.com
---
 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