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Date:   Fri, 6 Apr 2018 05:07:42 -0700
From:   Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     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,
        dnelson@redhat.com, Vadim Lomovtsev <Vadim.Lomovtsev@cavium.com>,
        gustavo@embeddedor.com
Subject: Re: [PATCH v2] net: thunderx: rework mac addresses list to u64 array
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Hi Robin,

On Fri, Apr 06, 2018 at 12:48:40PM +0100, Robin Murphy wrote:
> 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.
> 

Thanks for reviewing it and for hint. From style perspective, I believe,
I should get rid off direct types names also, and use your suggestion here.

I'll update patch to v3, test and re-post.
Thank you for your time.

WBR,
Vadim

> > +						  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++;
> >   				}
> >   			}
> >