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Subject: Re: [PATCH v2] net: thunderx: rework mac addresses list to u64 array
To:     Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com>,
        sgoutham@cavium.com, sunil.kovvuri@gmail.com, rric@kernel.org,
        linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, davem@davemloft.net
Cc:     dnelson@redhat.com, Vadim Lomovtsev <Vadim.Lomovtsev@cavium.com>,
        gustavo@embeddedor.com
References: <20180405145756.12633-1-Vadim.Lomovtsev@caviumnetworks.com>
 <20180406111425.14636-1-Vadim.Lomovtsev@caviumnetworks.com>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <32d75865-6407-9e9e-a78d-38ba761b2575@arm.com>
Date:   Fri, 6 Apr 2018 12:48:40 +0100
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On 06/04/18 12:14, Vadim Lomovtsev wrote:
> From: Vadim Lomovtsev <Vadim.Lomovtsev@cavium.com>
> 
> It is too expensive to pass u64 values via linked list, instead
> allocate array for them by overall number of mac addresses from netdev.
> 
> This eventually removes multiple kmalloc() calls, aviod memory
> fragmentation and allow to put single null check on kmalloc
> return value in order to prevent a potential null pointer dereference.
> 
> Addresses-Coverity-ID: 1467429 ("Dereference null return value")
> Fixes: 37c3347eb247 ("net: thunderx: add ndo_set_rx_mode callback implementation for VF")
> Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@cavium.com>
> ---
> Changes from v1 to v2:
>   - C99 syntax: update xcast_addr_list struct field mc[0] -> mc[];
> 
> ---
>   drivers/net/ethernet/cavium/thunder/nic.h        |  7 +-----
>   drivers/net/ethernet/cavium/thunder/nicvf_main.c | 28 +++++++++---------------
>   2 files changed, 11 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cavium/thunder/nic.h b/drivers/net/ethernet/cavium/thunder/nic.h
> index 5fc46c5a4f36..448d1fafc827 100644
> --- a/drivers/net/ethernet/cavium/thunder/nic.h
> +++ b/drivers/net/ethernet/cavium/thunder/nic.h
> @@ -265,14 +265,9 @@ struct nicvf_drv_stats {
>   
>   struct cavium_ptp;
>   
> -struct xcast_addr {
> -	struct list_head list;
> -	u64              addr;
> -};
> -
>   struct xcast_addr_list {
> -	struct list_head list;
>   	int              count;
> +	u64              mc[];
>   };
>   
>   struct nicvf_work {
> diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_main.c b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
> index 1e9a31fef729..a26d8bc92e01 100644
> --- a/drivers/net/ethernet/cavium/thunder/nicvf_main.c
> +++ b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
> @@ -1929,7 +1929,7 @@ static void nicvf_set_rx_mode_task(struct work_struct *work_arg)
>   						  work.work);
>   	struct nicvf *nic = container_of(vf_work, struct nicvf, rx_mode_work);
>   	union nic_mbx mbx = {};
> -	struct xcast_addr *xaddr, *next;
> +	u8 idx = 0;
>   
>   	if (!vf_work)
>   		return;
> @@ -1956,16 +1956,10 @@ static void nicvf_set_rx_mode_task(struct work_struct *work_arg)
>   	/* check if we have any specific MACs to be added to PF DMAC filter */
>   	if (vf_work->mc) {
>   		/* now go through kernel list of MACs and add them one by one */
> -		list_for_each_entry_safe(xaddr, next,
> -					 &vf_work->mc->list, list) {
> +		for (idx = 0; idx < vf_work->mc->count; idx++) {
>   			mbx.xcast.msg = NIC_MBOX_MSG_ADD_MCAST;
> -			mbx.xcast.data.mac = xaddr->addr;
> +			mbx.xcast.data.mac = vf_work->mc->mc[idx];
>   			nicvf_send_msg_to_pf(nic, &mbx);
> -
> -			/* after receiving ACK from PF release memory */
> -			list_del(&xaddr->list);
> -			kfree(xaddr);
> -			vf_work->mc->count--;
>   		}
>   		kfree(vf_work->mc);
>   	}
> @@ -1996,17 +1990,15 @@ static void nicvf_set_rx_mode(struct net_device *netdev)
>   			mode |= BGX_XCAST_MCAST_FILTER;
>   			/* here we need to copy mc addrs */
>   			if (netdev_mc_count(netdev)) {
> -				struct xcast_addr *xaddr;
> -
> -				mc_list = kmalloc(sizeof(*mc_list), GFP_ATOMIC);
> -				INIT_LIST_HEAD(&mc_list->list);
> +				mc_list = kmalloc(sizeof(*mc_list) +
> +						  sizeof(u64) * netdev_mc_count(netdev),

FWIW if you really wanted to disambiguate that it's a structure and not 
just an array being allocated, then it could be expressed without 
explicit arithmetic:

	size = offsetof(typeof(*mc_list), mc[netdev_mc_count(netdev)]);

but that's probably just a matter of personal preference at this point.

Robin.

> +						  GFP_ATOMIC);
> +				if (unlikely(!mc_list))
> +					return;
> +				mc_list->count = 0;
>   				netdev_hw_addr_list_for_each(ha, &netdev->mc) {
> -					xaddr = kmalloc(sizeof(*xaddr),
> -							GFP_ATOMIC);
> -					xaddr->addr =
> +					mc_list->mc[mc_list->count] =
>   						ether_addr_to_u64(ha->addr);
> -					list_add_tail(&xaddr->list,
> -						      &mc_list->list);
>   					mc_list->count++;
>   				}
>   			}
>