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

[Michal Swiatkowski <michal.swiatkowski@linux.intel.com>]

On Thu, Jan 09, 2025 at 04:45:04PM -0800, Jakub Kicinski wrote:
> 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@kernel.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@fastly.com
> CC: almasrymina@google.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;
>  

Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>

> -- 
> 2.47.1