[1/2] net: macb: reduce scope of rx_fs_lock-protected regions

Commit ae8223de3df5 ("net: macb: Added support for RX filtering")
introduces a lock, rx_fs_lock which is intended to protect the list of
rx_flow items and synchronize access to the hardware rx filtering
registers.

However, the region protected by this lock is overscoped, unnecessarily
including things like slab allocation.  Reduce this lock scope to only
include operations which must be performed atomically: list traversal,
addition, and removal, and hitting the macb filtering registers.

This fixes the use of kmalloc w/ GFP_KERNEL in atomic context.

Fixes: ae8223de3df5 ("net: macb: Added support for RX filtering")
Cc: Rafal Ozieblo <rafalo@cadence.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Julia Cartwright <julia@ni.com>
---
While Julia Lawall's cocci-generated patch fixes the problem, the right
solution is to obviate the problem altogether.

Thanks,
   The Other Julia

 drivers/net/ethernet/cadence/macb_main.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

On 05/12/2017 at 21:17, Julia Cartwright wrote:
> Commit ae8223de3df5 ("net: macb: Added support for RX filtering")
> introduces a lock, rx_fs_lock which is intended to protect the list of
> rx_flow items and synchronize access to the hardware rx filtering
> registers.
> 
> However, the region protected by this lock is overscoped, unnecessarily
> including things like slab allocation.  Reduce this lock scope to only
> include operations which must be performed atomically: list traversal,
> addition, and removal, and hitting the macb filtering registers.
> 
> This fixes the use of kmalloc w/ GFP_KERNEL in atomic context.
> 
> Fixes: ae8223de3df5 ("net: macb: Added support for RX filtering")
> Cc: Rafal Ozieblo <rafalo@cadence.com>
> Cc: Julia Lawall <julia.lawall@lip6.fr>
> Signed-off-by: Julia Cartwright <julia@ni.com>
> ---
> While Julia Lawall's cocci-generated patch fixes the problem, the right
> solution is to obviate the problem altogether.
> 
> Thanks,
>    The Other Julia

Julia,

Thanks for your patch, it seems good indeed. Here is my:
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>

As the patch by Julia L. is already in net-next, I suspect that you
would need to add a kind of revert patch if we want to come back to a
more usual GFP_KERNEL for the kmalloc.

Best regards,
  Nicolas

>  drivers/net/ethernet/cadence/macb_main.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index c5fa87cdc6c4..e7ef104a077d 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -2796,6 +2796,7 @@ static int gem_add_flow_filter(struct net_device *netdev,
>  	struct macb *bp = netdev_priv(netdev);
>  	struct ethtool_rx_flow_spec *fs = &cmd->fs;
>  	struct ethtool_rx_fs_item *item, *newfs;
> +	unsigned long flags;
>  	int ret = -EINVAL;
>  	bool added = false;
>  
> @@ -2811,6 +2812,8 @@ static int gem_add_flow_filter(struct net_device *netdev,
>  			htonl(fs->h_u.tcp_ip4_spec.ip4dst),
>  			htons(fs->h_u.tcp_ip4_spec.psrc), htons(fs->h_u.tcp_ip4_spec.pdst));
>  
> +	spin_lock_irqsave(&bp->rx_fs_lock, flags);
> +
>  	/* find correct place to add in list */
>  	if (list_empty(&bp->rx_fs_list.list))
>  		list_add(&newfs->list, &bp->rx_fs_list.list);
> @@ -2837,9 +2840,11 @@ static int gem_add_flow_filter(struct net_device *netdev,
>  	if (netdev->features & NETIF_F_NTUPLE)
>  		gem_enable_flow_filters(bp, 1);
>  
> +	spin_unlock_irqrestore(&bp->rx_fs_lock, flags);
>  	return 0;
>  
>  err:
> +	spin_unlock_irqrestore(&bp->rx_fs_lock, flags);
>  	kfree(newfs);
>  	return ret;
>  }
> @@ -2850,9 +2855,14 @@ static int gem_del_flow_filter(struct net_device *netdev,
>  	struct macb *bp = netdev_priv(netdev);
>  	struct ethtool_rx_fs_item *item;
>  	struct ethtool_rx_flow_spec *fs;
> +	unsigned long flags;
>  
> -	if (list_empty(&bp->rx_fs_list.list))
> +	spin_lock_irqsave(&bp->rx_fs_lock, flags);
> +
> +	if (list_empty(&bp->rx_fs_list.list)) {
> +		spin_unlock_irqrestore(&bp->rx_fs_lock, flags);
>  		return -EINVAL;
> +	}
>  
>  	list_for_each_entry(item, &bp->rx_fs_list.list, list) {
>  		if (item->fs.location == cmd->fs.location) {
> @@ -2869,12 +2879,14 @@ static int gem_del_flow_filter(struct net_device *netdev,
>  			gem_writel_n(bp, SCRT2, fs->location, 0);
>  
>  			list_del(&item->list);
> -			kfree(item);
>  			bp->rx_fs_list.count--;
> +			spin_unlock_irqrestore(&bp->rx_fs_lock, flags);
> +			kfree(item);
>  			return 0;
>  		}
>  	}
>  
> +	spin_unlock_irqrestore(&bp->rx_fs_lock, flags);
>  	return -EINVAL;
>  }
>  
> @@ -2943,11 +2955,8 @@ static int gem_get_rxnfc(struct net_device *netdev, struct ethtool_rxnfc *cmd,
>  static int gem_set_rxnfc(struct net_device *netdev, struct ethtool_rxnfc *cmd)
>  {
>  	struct macb *bp = netdev_priv(netdev);
> -	unsigned long flags;
>  	int ret;
>  
> -	spin_lock_irqsave(&bp->rx_fs_lock, flags);
> -
>  	switch (cmd->cmd) {
>  	case ETHTOOL_SRXCLSRLINS:
>  		if ((cmd->fs.location >= bp->max_tuples)
> @@ -2966,7 +2975,6 @@ static int gem_set_rxnfc(struct net_device *netdev, struct ethtool_rxnfc *cmd)
>  		ret = -EOPNOTSUPP;
>  	}
>  
> -	spin_unlock_irqrestore(&bp->rx_fs_lock, flags);
>  	return ret;
>  }
>  
>

From: Julia Cartwright <julia@ni.com>
Date: Tue, 5 Dec 2017 14:17:11 -0600

> While Julia Lawall's cocci-generated patch fixes the problem, the right
> solution is to obviate the problem altogether.

I already applied Julia's patch.  And I hope that if you generated
this against current net-next you would have seen that.

So you'll need to redo this series and put the GFP_KERNEL back.