linux-kernel - Re: [Intel-wired-lan] [PATCH net] idpf: Fix data race in idpf_net

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Message-ID: <8cfba7ca-03d0-46fe-92fa-5d4a119fc31e@molgen.mpg.de>
Date: Tue, 20 Jan 2026 17:50:05 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: David Yang <mmyangfl@...il.com>
Cc: netdev@...r.kernel.org, Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Pavan Kumar Linga <pavan.kumar.linga@...el.com>,
 Phani Burra <phani.r.burra@...el.com>, Willem de Bruijn
 <willemb@...gle.com>, Alan Brady <alan.brady@...el.com>,
 Sridhar Samudrala <sridhar.samudrala@...el.com>,
 Joshua Hay <joshua.a.hay@...el.com>, intel-wired-lan@...ts.osuosl.org,
 linux-kernel@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH net] idpf: Fix data race in idpf_net_dim

Dear David,

Thank you for your patch.

Am 19.01.26 um 17:27 schrieb David Yang:
> In idpf_net_dim(), some statistics protected by u64_stats_sync, are read
> and accumulated in ignorance of possible u64_stats_fetch_retry() events.
> The correct way to copy statistics is already illustrated by
> idpf_add_queue_stats(). Fix this by reading them into temporary variables
> first.

It’d be great if you also documented a test case.

> Fixes: c2d548cad150 ("idpf: add TX splitq napi poll support")
> Fixes: 3a8845af66ed ("idpf: add RX splitq napi poll support")
> Signed-off-by: David Yang <mmyangfl@...il.com>
> ---
>   drivers/net/ethernet/intel/idpf/idpf_txrx.c | 16 +++++++++++-----
>   1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> index 97a5fe766b6b..66ba645e8b90 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> @@ -3956,7 +3956,7 @@ static void idpf_update_dim_sample(struct idpf_q_vector *q_vector,
>   static void idpf_net_dim(struct idpf_q_vector *q_vector)
>   {
>   	struct dim_sample dim_sample = { };
> -	u64 packets, bytes;
> +	u64 packets, bytes, pkts, bts;

The new variable names are ambiguous. Would _tmp or so be better?

>   	u32 i;
>   
>   	if (!IDPF_ITR_IS_DYNAMIC(q_vector->tx_intr_mode))
> @@ -3968,9 +3968,12 @@ static void idpf_net_dim(struct idpf_q_vector *q_vector)
>   
>   		do {
>   			start = u64_stats_fetch_begin(&txq->stats_sync);
> -			packets += u64_stats_read(&txq->q_stats.packets);
> -			bytes += u64_stats_read(&txq->q_stats.bytes);
> +			pkts = u64_stats_read(&txq->q_stats.packets);
> +			bts = u64_stats_read(&txq->q_stats.bytes);
>   		} while (u64_stats_fetch_retry(&txq->stats_sync, start));
> +
> +		packets += pkts;
> +		bytes += bts;
>   	}
>   
>   	idpf_update_dim_sample(q_vector, &dim_sample, &q_vector->tx_dim,
> @@ -3987,9 +3990,12 @@ static void idpf_net_dim(struct idpf_q_vector *q_vector)
>   
>   		do {
>   			start = u64_stats_fetch_begin(&rxq->stats_sync);
> -			packets += u64_stats_read(&rxq->q_stats.packets);
> -			bytes += u64_stats_read(&rxq->q_stats.bytes);
> +			pkts = u64_stats_read(&rxq->q_stats.packets);
> +			bts = u64_stats_read(&rxq->q_stats.bytes);
>   		} while (u64_stats_fetch_retry(&rxq->stats_sync, start));
> +
> +		packets += pkts;
> +		bytes += bts;
>   	}
>   
>   	idpf_update_dim_sample(q_vector, &dim_sample, &q_vector->rx_dim,

Kind regards,

Paul