Re: [net-next 07/10] igb: Added rcu_lock to avoid race

[Eric Dumazet <eric.dumazet@gmail.com>]

On Wed, 2013-06-26 at 03:55 -0700, Jeff Kirsher wrote:
> From: "Akeem G. Abodunrin" <akeem.g.abodunrin@intel.com>
> 
> This patch adds rcu_lock to avoid possible race condition with igb_update_stats
> function accessing the rings in free_ q_vector.
> 
> Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
> Tested-by: Aaron Brown <aaron.f.brown@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index 7112e52..c74ad78 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -705,6 +705,8 @@ static void __exit igb_exit_module(void)
>  	dca_unregister_notify(&dca_notifier);
>  #endif
>  	pci_unregister_driver(&igb_driver);
> +
> +	rcu_barrier(); /* Wait for completion of call_rcu()'s */
>  }
>  

This is not needed.

If this is really needed, a better comment would be welcomed ;)


>  module_exit(igb_exit_module);
> @@ -1013,7 +1015,7 @@ static void igb_free_q_vector(struct igb_adapter *adapter, int v_idx)
>  	adapter->q_vector[v_idx] = NULL;
>  	netif_napi_del(&q_vector->napi);
>  
> -	/* ixgbe_get_stats64() might access the rings on this vector,
> +	/* igb_get_stats64() might access the rings on this vector,
>  	 * we must wait a grace period before freeing it.
>  	 */
>  	kfree_rcu(q_vector, rcu);
> @@ -4860,6 +4862,8 @@ void igb_update_stats(struct igb_adapter *adapter,
>  
>  	bytes = 0;
>  	packets = 0;
> +
> +	rcu_read_lock();
>  	for (i = 0; i < adapter->num_rx_queues; i++) {
>  		u32 rqdpc = rd32(E1000_RQDPC(i));
>  		struct igb_ring *ring = adapter->rx_ring[i];
> @@ -4895,6 +4899,7 @@ void igb_update_stats(struct igb_adapter *adapter,
>  	}
>  	net_stats->tx_bytes = bytes;
>  	net_stats->tx_packets = packets;
> +	rcu_read_unlock();
>  
>  	/* read stats registers */
>  	adapter->stats.crcerrs += rd32(E1000_CRCERRS);