netdev - Re: [net-next 05/13] igc: Check __IGC_PTP_TX_IN_PROGRESS instead of ptp_tx

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Date:   Fri, 26 Jun 2020 21:30:35 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     davem@...emloft.net, Andre Guedes <andre.guedes@...el.com>,
        netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
        Aaron Brown <aaron.f.brown@...el.com>
Subject: Re: [net-next 05/13] igc: Check __IGC_PTP_TX_IN_PROGRESS instead of
 ptp_tx_skb

On Fri, 26 Jun 2020 18:54:23 -0700 Jeff Kirsher wrote:
> From: Andre Guedes <andre.guedes@...el.com>
> 
> The __IGC_PTP_TX_IN_PROGRESS flag indicates we have a pending Tx
> timestamp. In some places, instead of checking that flag, we check
> adapter->ptp_tx_skb. This patch fixes those places to use the flag.
> 
> Quick note about igc_ptp_tx_hwtstamp() change: when that function is
> called, adapter->ptp_tx_skb is expected to be valid always so we
> WARN_ON_ONCE() in case it is not.
> 
> Quick note about igc_ptp_suspend() change: when suspending, we don't
> really need to check if there is a pending timestamp. We can simply
> clear it unconditionally.
> 
> Signed-off-by: Andre Guedes <andre.guedes@...el.com>
> Tested-by: Aaron Brown <aaron.f.brown@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> ---
>  drivers/net/ethernet/intel/igc/igc_ptp.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_ptp.c b/drivers/net/ethernet/intel/igc/igc_ptp.c
> index b1b23c6bf689..e65fdcf966b2 100644
> --- a/drivers/net/ethernet/intel/igc/igc_ptp.c
> +++ b/drivers/net/ethernet/intel/igc/igc_ptp.c
> @@ -404,9 +404,6 @@ void igc_ptp_tx_hang(struct igc_adapter *adapter)
>  	bool timeout = time_is_before_jiffies(adapter->ptp_tx_start +
>  					      IGC_PTP_TX_TIMEOUT);
>  
> -	if (!adapter->ptp_tx_skb)
> -		return;
> -
>  	if (!test_bit(__IGC_PTP_TX_IN_PROGRESS, &adapter->state))
>  		return;
>  
> @@ -435,6 +432,9 @@ static void igc_ptp_tx_hwtstamp(struct igc_adapter *adapter)
>  	struct igc_hw *hw = &adapter->hw;
>  	u64 regval;
>  
> +	if (WARN_ON_ONCE(!skb))
> +		return;
> +
>  	regval = rd32(IGC_TXSTMPL);
>  	regval |= (u64)rd32(IGC_TXSTMPH) << 32;
>  	igc_ptp_systim_to_hwtstamp(adapter, &shhwtstamps, regval);
> @@ -466,7 +466,7 @@ static void igc_ptp_tx_work(struct work_struct *work)
>  	struct igc_hw *hw = &adapter->hw;
>  	u32 tsynctxctl;
>  
> -	if (!adapter->ptp_tx_skb)
> +	if (!test_bit(__IGC_PTP_TX_IN_PROGRESS, &adapter->state))
>  		return;

Not that reading ptp_tx_skb is particularly correct here, but I think
it's better. See how they get set:

		if (adapter->tstamp_config.tx_type == HWTSTAMP_TX_ON &&
		    !test_and_set_bit_lock(__IGC_PTP_TX_IN_PROGRESS,
					   &adapter->state)) {
			skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
			tx_flags |= IGC_TX_FLAGS_TSTAMP;

			adapter->ptp_tx_skb = skb_get(skb);
			adapter->ptp_tx_start = jiffies;

bit is set first and other fields after. Since there is no locking here
we may just see the bit but none of the fields set.

>  	if (time_is_before_jiffies(adapter->ptp_tx_start +
> @@ -588,11 +588,9 @@ void igc_ptp_suspend(struct igc_adapter *adapter)
>  		return;
>  
>  	cancel_work_sync(&adapter->ptp_tx_work);
> -	if (adapter->ptp_tx_skb) {
> -		dev_kfree_skb_any(adapter->ptp_tx_skb);
> -		adapter->ptp_tx_skb = NULL;
> -		clear_bit_unlock(__IGC_PTP_TX_IN_PROGRESS, &adapter->state);
> -	}
> +	dev_kfree_skb_any(adapter->ptp_tx_skb);
> +	adapter->ptp_tx_skb = NULL;
> +	clear_bit_unlock(__IGC_PTP_TX_IN_PROGRESS, &adapter->state);
>  }
>  
>  /**