netdev - Re: [Intel-wired-lan] [PATCH 4/5] e1000e: Separate signaling for link check/link up

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Date:   Wed, 2 Aug 2017 14:28:07 +0300
From:   "Neftin, Sasha" <sasha.neftin@...el.com>
To:     Benjamin Poirier <bpoirier@...e.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        linux-kernel@...r.kernel.org,
        Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Subject: Re: [Intel-wired-lan] [PATCH 4/5] e1000e: Separate signaling for link
 check/link up

On 7/21/2017 21:36, Benjamin Poirier wrote:
> Lennart reported the following race condition:
>
> \ e1000_watchdog_task
>      \ e1000e_has_link
>          \ hw->mac.ops.check_for_link() === e1000e_check_for_copper_link
>              /* link is up */
>              mac->get_link_status = false;
>
>                              /* interrupt */
>                              \ e1000_msix_other
>                                  hw->mac.get_link_status = true;
>
>          link_active = !hw->mac.get_link_status
>          /* link_active is false, wrongly */
>
> This problem arises because the single flag get_link_status is used to
> signal two different states: link status needs checking and link status is
> down.
>
> Avoid the problem by using the return value of .check_for_link to signal
> the link status to e1000e_has_link().
>
> Reported-by: Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
> Signed-off-by: Benjamin Poirier <bpoirier@...e.com>
> ---
>   drivers/net/ethernet/intel/e1000e/mac.c    | 11 ++++++++---
>   drivers/net/ethernet/intel/e1000e/netdev.c |  2 +-
>   2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/e1000e/mac.c b/drivers/net/ethernet/intel/e1000e/mac.c
> index b322011ec282..f457c5703d0c 100644
> --- a/drivers/net/ethernet/intel/e1000e/mac.c
> +++ b/drivers/net/ethernet/intel/e1000e/mac.c
> @@ -410,6 +410,9 @@ void e1000e_clear_hw_cntrs_base(struct e1000_hw *hw)
>    *  Checks to see of the link status of the hardware has changed.  If a
>    *  change in link status has been detected, then we read the PHY registers
>    *  to get the current speed/duplex if link exists.
> + *
> + *  Returns a negative error code (-E1000_ERR_*) or 0 (link down) or 1 (link
> + *  up).
>    **/
>   s32 e1000e_check_for_copper_link(struct e1000_hw *hw)
>   {
> @@ -423,7 +426,7 @@ s32 e1000e_check_for_copper_link(struct e1000_hw *hw)
>   	 * Change or Rx Sequence Error interrupt.
>   	 */
>   	if (!mac->get_link_status)
> -		return 0;
> +		return 1;
>   
>   	/* First we want to see if the MII Status Register reports
>   	 * link.  If so, then we want to get the current speed/duplex
> @@ -461,10 +464,12 @@ s32 e1000e_check_for_copper_link(struct e1000_hw *hw)
>   	 * different link partner.
>   	 */
>   	ret_val = e1000e_config_fc_after_link_up(hw);
> -	if (ret_val)
> +	if (ret_val) {
>   		e_dbg("Error configuring flow control\n");
> +		return ret_val;
> +	}
>   
> -	return ret_val;
> +	return 1;
>   }
>   
>   /**
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
> index fc6a1d9999b2..5a8ab1136566 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -5081,7 +5081,7 @@ static bool e1000e_has_link(struct e1000_adapter *adapter)
>   	case e1000_media_type_copper:
>   		if (hw->mac.get_link_status) {
>   			ret_val = hw->mac.ops.check_for_link(hw);
> -			link_active = !hw->mac.get_link_status;
> +			link_active = ret_val > 0;
>   		} else {
>   			link_active = true;
>   		}

Hello Benjamin,

Will this patch fix any serious problem with link indication? Is it 
necessary? Can we consider your patch series without 4/5 part?