netdev - Re: [PATCH net-next v3 1/9] tsnep: Use spin_lock

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Date:   Thu, 5 Jan 2023 13:40:17 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <edumazet@...gle.com>,
        <pabeni@...hat.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v3 1/9] tsnep: Use spin_lock_bh for TX

From: Gerhard Engleder <gerhard@...leder-embedded.com>
Date: Wed Jan 04 2023 20:41:24 GMT+0100

> TX processing is done only within process or BH context. Therefore,
> _irqsafe variant is not necessary.

NAPI and .ndo_{start,xdp}_xmit are BH-only, where can the process
context happen here?

> 
> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
> ---
>  drivers/net/ethernet/engleder/tsnep_main.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
> index bf0190e1d2ea..7cc5e2407809 100644
> --- a/drivers/net/ethernet/engleder/tsnep_main.c
> +++ b/drivers/net/ethernet/engleder/tsnep_main.c
> @@ -434,7 +434,6 @@ static int tsnep_tx_unmap(struct tsnep_tx *tx, int index, int count)
>  static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  					 struct tsnep_tx *tx)
>  {
> -	unsigned long flags;
>  	int count = 1;
>  	struct tsnep_tx_entry *entry;
>  	int length;
> @@ -444,7 +443,7 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  	if (skb_shinfo(skb)->nr_frags > 0)
>  		count += skb_shinfo(skb)->nr_frags;
>  
> -	spin_lock_irqsave(&tx->lock, flags);
> +	spin_lock_bh(&tx->lock);
>  
>  	if (tsnep_tx_desc_available(tx) < count) {
>  		/* ring full, shall not happen because queue is stopped if full
> @@ -452,7 +451,7 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  		 */
>  		netif_stop_queue(tx->adapter->netdev);
>  
> -		spin_unlock_irqrestore(&tx->lock, flags);
> +		spin_unlock_bh(&tx->lock);
>  
>  		return NETDEV_TX_BUSY;
>  	}
> @@ -468,7 +467,7 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  
>  		tx->dropped++;
>  
> -		spin_unlock_irqrestore(&tx->lock, flags);
> +		spin_unlock_bh(&tx->lock);
>  
>  		netdev_err(tx->adapter->netdev, "TX DMA map failed\n");
>  
> @@ -496,20 +495,19 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  		netif_stop_queue(tx->adapter->netdev);
>  	}
>  
> -	spin_unlock_irqrestore(&tx->lock, flags);
> +	spin_unlock_bh(&tx->lock);
>  
>  	return NETDEV_TX_OK;
>  }
>  
>  static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
>  {
> -	unsigned long flags;
>  	int budget = 128;
>  	struct tsnep_tx_entry *entry;
>  	int count;
>  	int length;
>  
> -	spin_lock_irqsave(&tx->lock, flags);
> +	spin_lock_bh(&tx->lock);
>  
>  	do {
>  		if (tx->read == tx->write)
> @@ -568,18 +566,17 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
>  		netif_wake_queue(tx->adapter->netdev);
>  	}
>  
> -	spin_unlock_irqrestore(&tx->lock, flags);
> +	spin_unlock_bh(&tx->lock);
>  
>  	return (budget != 0);
>  }
>  
>  static bool tsnep_tx_pending(struct tsnep_tx *tx)
>  {
> -	unsigned long flags;
>  	struct tsnep_tx_entry *entry;
>  	bool pending = false;
>  
> -	spin_lock_irqsave(&tx->lock, flags);
> +	spin_lock_bh(&tx->lock);
>  
>  	if (tx->read != tx->write) {
>  		entry = &tx->entry[tx->read];
> @@ -589,7 +586,7 @@ static bool tsnep_tx_pending(struct tsnep_tx *tx)
>  			pending = true;
>  	}
>  
> -	spin_unlock_irqrestore(&tx->lock, flags);
> +	spin_unlock_bh(&tx->lock);
>  
>  	return pending;
>  }

Thanks,
Olek