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Date: Tue, 30 May 2017 13:59:03 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com,
"David S. Miller" <davem@...emloft.net>,
Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next v2 6/6] net: dsa: factor skb freeing on xmit
On 05/30/2017 11:33 AM, Vivien Didelot wrote:
> The taggers are currently responsible to free the original SKB if they
> made a copy of it, or in case of error.
>
> This patch simplifies this by freeing the original SKB in the
> dsa_slave_xmit caller, but only if an error (NULL) is returned.
Is not it a clearer contract if the tagging protocol must always free
the original SKB, whether it succeeded in creating a new one or not?
>
> It is still the responsibility of the tagger to free the original SKB if
> it returned a copy of it.
>
> At the same time, fix the checkpatch NULL comparison check:
>
> CHECK: Comparison to NULL could be written "!nskb"
> #208: FILE: net/dsa/tag_trailer.c:35:
> + if (nskb == NULL)
>
> Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
> ---
> net/dsa/slave.c | 8 ++++++--
> net/dsa/tag_brcm.c | 6 +-----
> net/dsa/tag_dsa.c | 8 ++------
> net/dsa/tag_edsa.c | 8 ++------
> net/dsa/tag_lan9303.c | 5 +----
> net/dsa/tag_mtk.c | 6 +-----
> net/dsa/tag_qca.c | 6 +-----
> net/dsa/tag_trailer.c | 4 +---
> 8 files changed, 15 insertions(+), 36 deletions(-)
>
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 887e26695519..4473aec9dcda 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -362,10 +362,14 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
> dev->stats.tx_packets++;
> dev->stats.tx_bytes += skb->len;
>
> - /* Transmit function may have to reallocate the original SKB */
> + /* Transmit function may have to reallocate the original SKB,
> + * in which case it must have freed it. Only free it here on error.
> + */
> nskb = p->xmit(skb, dev);
> - if (!nskb)
> + if (!nskb) {
> + kfree_skb(skb);
> return NETDEV_TX_OK;
> + }
>
> /* SKB for netpoll still need to be mangled with the protocol-specific
> * tag to be successfully transmitted
> diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
> index 10fa4c0ca46b..5db6bcfde025 100644
> --- a/net/dsa/tag_brcm.c
> +++ b/net/dsa/tag_brcm.c
> @@ -65,7 +65,7 @@ static struct sk_buff *brcm_tag_xmit(struct sk_buff *skb, struct net_device *dev
> u8 *brcm_tag;
>
> if (skb_cow_head(skb, BRCM_TAG_LEN) < 0)
> - goto out_free;
> + return NULL;
>
> skb_push(skb, BRCM_TAG_LEN);
>
> @@ -86,10 +86,6 @@ static struct sk_buff *brcm_tag_xmit(struct sk_buff *skb, struct net_device *dev
> brcm_tag[3] = (1 << p->dp->index) & BRCM_IG_DSTMAP1_MASK;
>
> return skb;
> -
> -out_free:
> - kfree_skb(skb);
> - return NULL;
> }
>
> static struct sk_buff *brcm_tag_rcv(struct sk_buff *skb, struct net_device *dev)
> diff --git a/net/dsa/tag_dsa.c b/net/dsa/tag_dsa.c
> index 9f5fecaa4a93..6837ca9160a8 100644
> --- a/net/dsa/tag_dsa.c
> +++ b/net/dsa/tag_dsa.c
> @@ -28,7 +28,7 @@ static struct sk_buff *dsa_xmit(struct sk_buff *skb, struct net_device *dev)
> */
> if (skb->protocol == htons(ETH_P_8021Q)) {
> if (skb_cow_head(skb, 0) < 0)
> - goto out_free;
> + return NULL;
>
> /*
> * Construct tagged FROM_CPU DSA tag from 802.1q tag.
> @@ -46,7 +46,7 @@ static struct sk_buff *dsa_xmit(struct sk_buff *skb, struct net_device *dev)
> }
> } else {
> if (skb_cow_head(skb, DSA_HLEN) < 0)
> - goto out_free;
> + return NULL;
> skb_push(skb, DSA_HLEN);
>
> memmove(skb->data, skb->data + DSA_HLEN, 2 * ETH_ALEN);
> @@ -62,10 +62,6 @@ static struct sk_buff *dsa_xmit(struct sk_buff *skb, struct net_device *dev)
> }
>
> return skb;
> -
> -out_free:
> - kfree_skb(skb);
> - return NULL;
> }
>
> static struct sk_buff *dsa_rcv(struct sk_buff *skb, struct net_device *dev)
> diff --git a/net/dsa/tag_edsa.c b/net/dsa/tag_edsa.c
> index a9a06e19abeb..96ddc90472a2 100644
> --- a/net/dsa/tag_edsa.c
> +++ b/net/dsa/tag_edsa.c
> @@ -30,7 +30,7 @@ static struct sk_buff *edsa_xmit(struct sk_buff *skb, struct net_device *dev)
> */
> if (skb->protocol == htons(ETH_P_8021Q)) {
> if (skb_cow_head(skb, DSA_HLEN) < 0)
> - goto out_free;
> + return NULL;
> skb_push(skb, DSA_HLEN);
>
> memmove(skb->data, skb->data + DSA_HLEN, 2 * ETH_ALEN);
> @@ -55,7 +55,7 @@ static struct sk_buff *edsa_xmit(struct sk_buff *skb, struct net_device *dev)
> }
> } else {
> if (skb_cow_head(skb, EDSA_HLEN) < 0)
> - goto out_free;
> + return NULL;
> skb_push(skb, EDSA_HLEN);
>
> memmove(skb->data, skb->data + EDSA_HLEN, 2 * ETH_ALEN);
> @@ -75,10 +75,6 @@ static struct sk_buff *edsa_xmit(struct sk_buff *skb, struct net_device *dev)
> }
>
> return skb;
> -
> -out_free:
> - kfree_skb(skb);
> - return NULL;
> }
>
> static struct sk_buff *edsa_rcv(struct sk_buff *skb, struct net_device *dev)
> diff --git a/net/dsa/tag_lan9303.c b/net/dsa/tag_lan9303.c
> index 82e150486497..e33348101e8f 100644
> --- a/net/dsa/tag_lan9303.c
> +++ b/net/dsa/tag_lan9303.c
> @@ -52,7 +52,7 @@ static struct sk_buff *lan9303_xmit(struct sk_buff *skb, struct net_device *dev)
> if (skb_cow_head(skb, LAN9303_TAG_LEN) < 0) {
> dev_dbg(&dev->dev,
> "Cannot make room for the special tag. Dropping packet\n");
> - goto out_free;
> + return NULL;
> }
>
> /* provide 'LAN9303_TAG_LEN' bytes additional space */
> @@ -66,9 +66,6 @@ static struct sk_buff *lan9303_xmit(struct sk_buff *skb, struct net_device *dev)
> lan9303_tag[1] = htons(p->dp->index | BIT(4));
>
> return skb;
> -out_free:
> - kfree_skb(skb);
> - return NULL;
> }
>
> static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev)
> diff --git a/net/dsa/tag_mtk.c b/net/dsa/tag_mtk.c
> index 327dd7b596df..ee62ae5f03e1 100644
> --- a/net/dsa/tag_mtk.c
> +++ b/net/dsa/tag_mtk.c
> @@ -27,7 +27,7 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
> u8 *mtk_tag;
>
> if (skb_cow_head(skb, MTK_HDR_LEN) < 0)
> - goto out_free;
> + return NULL;
>
> skb_push(skb, MTK_HDR_LEN);
>
> @@ -41,10 +41,6 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
> mtk_tag[3] = 0;
>
> return skb;
> -
> -out_free:
> - kfree_skb(skb);
> - return NULL;
> }
>
> static struct sk_buff *mtk_tag_rcv(struct sk_buff *skb, struct net_device *dev)
> diff --git a/net/dsa/tag_qca.c b/net/dsa/tag_qca.c
> index 8080ad8f2abb..4d3bc2920477 100644
> --- a/net/dsa/tag_qca.c
> +++ b/net/dsa/tag_qca.c
> @@ -45,7 +45,7 @@ static struct sk_buff *qca_tag_xmit(struct sk_buff *skb, struct net_device *dev)
> dev->stats.tx_bytes += skb->len;
>
> if (skb_cow_head(skb, 0) < 0)
> - goto out_free;
> + return NULL;
>
> skb_push(skb, QCA_HDR_LEN);
>
> @@ -60,10 +60,6 @@ static struct sk_buff *qca_tag_xmit(struct sk_buff *skb, struct net_device *dev)
> *phdr = htons(hdr);
>
> return skb;
> -
> -out_free:
> - kfree_skb(skb);
> - return NULL;
> }
>
> static struct sk_buff *qca_tag_rcv(struct sk_buff *skb, struct net_device *dev)
> diff --git a/net/dsa/tag_trailer.c b/net/dsa/tag_trailer.c
> index 7422b1329712..8c9a7f5ecc66 100644
> --- a/net/dsa/tag_trailer.c
> +++ b/net/dsa/tag_trailer.c
> @@ -32,10 +32,8 @@ static struct sk_buff *trailer_xmit(struct sk_buff *skb, struct net_device *dev)
> padlen = 60 - skb->len;
>
> nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + 4, GFP_ATOMIC);
> - if (nskb == NULL) {
> - kfree_skb(skb);
> + if (!nskb)
> return NULL;
> - }
> skb_reserve(nskb, NET_IP_ALIGN);
>
> skb_reset_mac_header(nskb);
>
--
Florian
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