stmmac: limit max_mtu in case of 4KiB and use __netdev_alloc_skb (V2)

Problem using big mtu around 4096 bytes is you end allocating (4096
+NET_SKB_PAD + NET_IP_ALIGN + sizeof(struct skb_shared_info) bytes ->
8192 bytes : order-1 pages

It's better to limit the mtu to SKB_MAX_HEAD(NET_SKB_PAD),
to have no more than one page per skb.

Also the patch changes the netdev_alloc_skb_ip_align() done in
init_dma_desc_rings() and uses a variant allowing GFP_KERNEL allocations
allowing the driver to load even in case of memory pressure.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 5eccd996cde..aeaa15b451d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -474,11 +474,13 @@ static void init_dma_desc_rings(struct net_device *dev)
         for (i = 0; i < rxsize; i++) {
                 struct dma_desc *p = priv->dma_rx + i;
 
-                skb = netdev_alloc_skb_ip_align(dev, bfsize);
+                skb = __netdev_alloc_skb(dev, bfsize + NET_IP_ALIGN,
+                                         GFP_KERNEL);
                 if (unlikely(skb == NULL)) {
                         pr_err("%s: Rx init fails; skb is NULL\n", __func__);
                         break;
                 }
+                skb_reserve(skb, NET_IP_ALIGN);
                 priv->rx_skbuff[i] = skb;
                 priv->rx_skbuff_dma[i] = dma_map_single(priv->device, skb->data,
                                                 bfsize, DMA_FROM_DEVICE);
@@ -1401,7 +1403,7 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
         if (priv->plat->enh_desc)
                 max_mtu = JUMBO_LEN;
         else
-                max_mtu = BUF_SIZE_4KiB;
+                max_mtu = SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN);
 
         if ((new_mtu < 46) || (new_mtu > max_mtu)) {
                 pr_err("%s: invalid MTU, max MTU is: %d\n", dev->name, max_mtu);