netdev - Re: [PATCH net v2] net: openvswitch: fix data race in ovs_vport_get_upcall

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Message-ID: <a71f371d-7f80-4660-ab4c-b022468c6dff@ovn.org>
Date: Wed, 21 Jan 2026 14:27:51 +0100
From: Ilya Maximets <i.maximets@....org>
To: David Yang <mmyangfl@...il.com>, netdev@...r.kernel.org
Cc: i.maximets@....org, Aaron Conole <aconole@...hat.com>,
 Eelco Chaudron <echaudro@...hat.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, wangchuanlei <wangchuanlei@...pur.com>,
 dev@...nvswitch.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: openvswitch: fix data race in
 ovs_vport_get_upcall_stats

On 1/21/26 8:29 AM, David Yang wrote:
> In ovs_vport_get_upcall_stats(), some statistics protected by
> u64_stats_sync, are read and accumulated in ignorance of possible
> u64_stats_fetch_retry() events. These statistics are already accumulated
> by u64_stats_inc(). Fix this by reading them into temporary variables
> first.
> 
> Fixes: 1933ea365aa7 ("net: openvswitch: Add support to count upcall packets")
> Signed-off-by: David Yang <mmyangfl@...il.com>
> ---
> v1: https://lore.kernel.org/r/20260119181339.1847451-1-mmyangfl@gmail.com
>   - use u64 instead of __u64
>  net/openvswitch/vport.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
> index 6bbbc16ab778..f0ce8ce1dce0 100644
> --- a/net/openvswitch/vport.c
> +++ b/net/openvswitch/vport.c
> @@ -310,22 +310,23 @@ void ovs_vport_get_stats(struct vport *vport, struct ovs_vport_stats *stats)
>   */
>  int ovs_vport_get_upcall_stats(struct vport *vport, struct sk_buff *skb)
>  {
> +	u64 tx_success = 0, tx_fail = 0;
>  	struct nlattr *nla;
>  	int i;
>  
> -	__u64 tx_success = 0;
> -	__u64 tx_fail = 0;
> -
>  	for_each_possible_cpu(i) {
>  		const struct vport_upcall_stats_percpu *stats;
> +		u64 n_success, n_fail;
>  		unsigned int start;
>  
>  		stats = per_cpu_ptr(vport->upcall_stats, i);
>  		do {
>  			start = u64_stats_fetch_begin(&stats->syncp);
> -			tx_success += u64_stats_read(&stats->n_success);
> -			tx_fail += u64_stats_read(&stats->n_fail);
> +			n_success = u64_stats_read(&stats->n_success);
> +			n_fail = u64_stats_read(&stats->n_fail);
>  		} while (u64_stats_fetch_retry(&stats->syncp, start));

Would be good to have an empty line here for readability, but a new version
just for this seems a bit excessive.

Either way:

Acked-by: Ilya Maximets <i.maximets@....org>

> +		tx_success += n_success;
> +		tx_fail += n_fail;
>  	}
>  
>  	nla = nla_nest_start_noflag(skb, OVS_VPORT_ATTR_UPCALL_STATS);