Re: [net-next, v2, 3/7] net: dsa: free skb->cb usage in core driver

From: Tobias Waldekranz
Date: Wed Apr 28 2021 - 16:30:05 EST

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In reply to: Y.b. Lu: "RE: [net-next, v2, 3/7] net: dsa: free skb->cb usage in core driver"
Next in thread: Yangbo Lu: "[net-next, v2, 7/7] net: mscc: ocelot: support PTP Sync one-step timestamping"
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On Mon, Apr 26, 2021 at 17:37, Yangbo Lu <yangbo.lu@xxxxxxx> wrote:
> Free skb->cb usage in core driver and let device drivers decide to
> use or not. The reason having a DSA_SKB_CB(skb)->clone was because
> dsa_skb_tx_timestamp() which may set the clone pointer was called
> before p->xmit() which would use the clone if any, and the device
> driver has no way to initialize the clone pointer.
>
> Although for now putting memset(skb->cb, 0, 48) at beginning of
> dsa_slave_xmit() by this patch is not very good, there is still way
> to improve this. Otherwise, some other new features, like one-step

Could you please expand on this improvement?

This memset makes it impossible to carry control buffer information from
driver callbacks that run before .ndo_start_xmit, for example
.ndo_select_queue, to a tagger's .xmit.

It seems to me that if the drivers are to handle the CB internally from
now on, that should go for both setting and clearing of the required
fields.

> timestamp which needs a flag of skb marked in dsa_skb_tx_timestamp(),
> and handles as one-step timestamp in p->xmit() will face same
> situation.
>
> Signed-off-by: Yangbo Lu <yangbo.lu@xxxxxxx>
> ---
> Changes for v2:
> - Added this patch.
> ---
> drivers/net/dsa/ocelot/felix.c | 1 +
> drivers/net/dsa/sja1105/sja1105_main.c | 2 +-
> drivers/net/dsa/sja1105/sja1105_ptp.c | 4 +++-
> drivers/net/ethernet/mscc/ocelot.c | 6 +++---
> drivers/net/ethernet/mscc/ocelot_net.c | 2 +-
> include/linux/dsa/sja1105.h | 3 ++-
> include/net/dsa.h | 14 --------------
> include/soc/mscc/ocelot.h | 8 ++++++++
> net/dsa/slave.c | 3 +--
> net/dsa/tag_ocelot.c | 8 ++++----
> net/dsa/tag_ocelot_8021q.c | 8 ++++----
> 11 files changed, 28 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
> index d679f023dc00..8980d56ee793 100644
> --- a/drivers/net/dsa/ocelot/felix.c
> +++ b/drivers/net/dsa/ocelot/felix.c
> @@ -1403,6 +1403,7 @@ static bool felix_txtstamp(struct dsa_switch *ds, int port,
>
> if (ocelot->ptp && ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP) {
> ocelot_port_add_txtstamp_skb(ocelot, port, clone);
> + OCELOT_SKB_CB(skb)->clone = clone;
> return true;
> }
>
> diff --git a/drivers/net/dsa/sja1105/sja1105_main.c b/drivers/net/dsa/sja1105/sja1105_main.c
> index d9c198ca0197..405024b637d6 100644
> --- a/drivers/net/dsa/sja1105/sja1105_main.c
> +++ b/drivers/net/dsa/sja1105/sja1105_main.c
> @@ -3137,7 +3137,7 @@ static void sja1105_port_deferred_xmit(struct kthread_work *work)
> struct sk_buff *skb;
>
> while ((skb = skb_dequeue(&sp->xmit_queue)) != NULL) {
> - struct sk_buff *clone = DSA_SKB_CB(skb)->clone;
> + struct sk_buff *clone = SJA1105_SKB_CB(skb)->clone;
>
> mutex_lock(&priv->mgmt_lock);
>
> diff --git a/drivers/net/dsa/sja1105/sja1105_ptp.c b/drivers/net/dsa/sja1105/sja1105_ptp.c
> index 72d052de82d8..0832368aaa96 100644
> --- a/drivers/net/dsa/sja1105/sja1105_ptp.c
> +++ b/drivers/net/dsa/sja1105/sja1105_ptp.c
> @@ -432,7 +432,7 @@ bool sja1105_port_rxtstamp(struct dsa_switch *ds, int port,
> }
>
> /* Called from dsa_skb_tx_timestamp. This callback is just to make DSA clone
> - * the skb and have it available in DSA_SKB_CB in the .port_deferred_xmit
> + * the skb and have it available in SJA1105_SKB_CB in the .port_deferred_xmit
> * callback, where we will timestamp it synchronously.
> */
> bool sja1105_port_txtstamp(struct dsa_switch *ds, int port, struct sk_buff *skb)
> @@ -443,6 +443,8 @@ bool sja1105_port_txtstamp(struct dsa_switch *ds, int port, struct sk_buff *skb)
> if (!sp->hwts_tx_en)
> return false;
>
> + SJA1105_SKB_CB(skb)->clone = clone;
> +
> return true;
> }
>
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index 8d06ffaf318a..7da2dd1632b1 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -538,8 +538,8 @@ void ocelot_port_add_txtstamp_skb(struct ocelot *ocelot, int port,
> spin_lock(&ocelot_port->ts_id_lock);
>
> skb_shinfo(clone)->tx_flags |= SKBTX_IN_PROGRESS;
> - /* Store timestamp ID in cb[0] of sk_buff */
> - clone->cb[0] = ocelot_port->ts_id;
> + /* Store timestamp ID in OCELOT_SKB_CB(clone)->ts_id */
> + OCELOT_SKB_CB(clone)->ts_id = ocelot_port->ts_id;
> ocelot_port->ts_id = (ocelot_port->ts_id + 1) % 4;
> skb_queue_tail(&ocelot_port->tx_skbs, clone);
>
> @@ -604,7 +604,7 @@ void ocelot_get_txtstamp(struct ocelot *ocelot)
> spin_lock_irqsave(&port->tx_skbs.lock, flags);
>
> skb_queue_walk_safe(&port->tx_skbs, skb, skb_tmp) {
> - if (skb->cb[0] != id)
> + if (OCELOT_SKB_CB(skb)->ts_id != id)
> continue;
> __skb_unlink(skb, &port->tx_skbs);
> skb_match = skb;
> diff --git a/drivers/net/ethernet/mscc/ocelot_net.c b/drivers/net/ethernet/mscc/ocelot_net.c
> index 36f32a4d9b0f..789a5fba146c 100644
> --- a/drivers/net/ethernet/mscc/ocelot_net.c
> +++ b/drivers/net/ethernet/mscc/ocelot_net.c
> @@ -520,7 +520,7 @@ static netdev_tx_t ocelot_port_xmit(struct sk_buff *skb, struct net_device *dev)
>
> ocelot_port_add_txtstamp_skb(ocelot, port, clone);
>
> - rew_op |= clone->cb[0] << 3;
> + rew_op |= OCELOT_SKB_CB(clone)->ts_id << 3;
> }
> }
>
> diff --git a/include/linux/dsa/sja1105.h b/include/linux/dsa/sja1105.h
> index dd93735ae228..1eb84562b311 100644
> --- a/include/linux/dsa/sja1105.h
> +++ b/include/linux/dsa/sja1105.h
> @@ -47,11 +47,12 @@ struct sja1105_tagger_data {
> };
>
> struct sja1105_skb_cb {
> + struct sk_buff *clone;
> u32 meta_tstamp;
> };
>
> #define SJA1105_SKB_CB(skb) \
> - ((struct sja1105_skb_cb *)DSA_SKB_CB_PRIV(skb))
> + ((struct sja1105_skb_cb *)((skb)->cb))
>
> struct sja1105_port {
> u16 subvlan_map[DSA_8021Q_N_SUBVLAN];
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 905066055b08..5685e60cb082 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -117,20 +117,6 @@ struct dsa_netdevice_ops {
> #define MODULE_ALIAS_DSA_TAG_DRIVER(__proto) \
> MODULE_ALIAS(DSA_TAG_DRIVER_ALIAS __stringify(__proto##_VALUE))
>
> -struct dsa_skb_cb {
> - struct sk_buff *clone;
> -};
> -
> -struct __dsa_skb_cb {
> - struct dsa_skb_cb cb;
> - u8 priv[48 - sizeof(struct dsa_skb_cb)];
> -};
> -
> -#define DSA_SKB_CB(skb) ((struct dsa_skb_cb *)((skb)->cb))
> -
> -#define DSA_SKB_CB_PRIV(skb) \
> - ((void *)(skb)->cb + offsetof(struct __dsa_skb_cb, priv))
> -
> struct dsa_switch_tree {
> struct list_head list;
>
> diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
> index 68cdc7ceaf4d..f075aaf70eee 100644
> --- a/include/soc/mscc/ocelot.h
> +++ b/include/soc/mscc/ocelot.h
> @@ -689,6 +689,14 @@ struct ocelot_policer {
> u32 burst; /* bytes */
> };
>
> +struct ocelot_skb_cb {
> + struct sk_buff *clone;
> + u8 ts_id;
> +};
> +
> +#define OCELOT_SKB_CB(skb) \
> + ((struct ocelot_skb_cb *)((skb)->cb))
> +
> #define ocelot_read_ix(ocelot, reg, gi, ri) __ocelot_read_ix(ocelot, reg, reg##_GSZ * (gi) + reg##_RSZ * (ri))
> #define ocelot_read_gix(ocelot, reg, gi) __ocelot_read_ix(ocelot, reg, reg##_GSZ * (gi))
> #define ocelot_read_rix(ocelot, reg, ri) __ocelot_read_ix(ocelot, reg, reg##_RSZ * (ri))
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index acaa52e60d7f..2211894c2381 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -568,7 +568,6 @@ static void dsa_skb_tx_timestamp(struct dsa_slave_priv *p,
> return;
>
> if (ds->ops->port_txtstamp(ds, p->dp->index, clone)) {
> - DSA_SKB_CB(skb)->clone = clone;
> return;
> }
>
> @@ -624,7 +623,7 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
>
> dev_sw_netstats_tx_add(dev, 1, skb->len);
>
> - DSA_SKB_CB(skb)->clone = NULL;
> + memset(skb->cb, 0, 48);
>
> /* Handle tx timestamp if any */
> dsa_skb_tx_timestamp(p, skb);
> diff --git a/net/dsa/tag_ocelot.c b/net/dsa/tag_ocelot.c
> index f9df9cac81c5..1100a16f1032 100644
> --- a/net/dsa/tag_ocelot.c
> +++ b/net/dsa/tag_ocelot.c
> @@ -15,11 +15,11 @@ static void ocelot_xmit_ptp(struct dsa_port *dp, void *injection,
> ocelot_port = ocelot->ports[dp->index];
> rew_op = ocelot_port->ptp_cmd;
>
> - /* Retrieve timestamp ID populated inside skb->cb[0] of the
> - * clone by ocelot_port_add_txtstamp_skb
> + /* Retrieve timestamp ID populated inside OCELOT_SKB_CB(clone)->ts_id
> + * by ocelot_port_add_txtstamp_skb
> */
> if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
> - rew_op |= clone->cb[0] << 3;
> + rew_op |= OCELOT_SKB_CB(clone)->ts_id << 3;
>
> ocelot_ifh_set_rew_op(injection, rew_op);
> }
> @@ -28,7 +28,7 @@ static void ocelot_xmit_common(struct sk_buff *skb, struct net_device *netdev,
> __be32 ifh_prefix, void **ifh)
> {
> struct dsa_port *dp = dsa_slave_to_port(netdev);
> - struct sk_buff *clone = DSA_SKB_CB(skb)->clone;
> + struct sk_buff *clone = OCELOT_SKB_CB(skb)->clone;
> struct dsa_switch *ds = dp->ds;
> void *injection;
> __be32 *prefix;
> diff --git a/net/dsa/tag_ocelot_8021q.c b/net/dsa/tag_ocelot_8021q.c
> index 5f3e8e124a82..a001a7e3f575 100644
> --- a/net/dsa/tag_ocelot_8021q.c
> +++ b/net/dsa/tag_ocelot_8021q.c
> @@ -28,11 +28,11 @@ static struct sk_buff *ocelot_xmit_ptp(struct dsa_port *dp,
> ocelot_port = ocelot->ports[port];
> rew_op = ocelot_port->ptp_cmd;
>
> - /* Retrieve timestamp ID populated inside skb->cb[0] of the
> - * clone by ocelot_port_add_txtstamp_skb
> + /* Retrieve timestamp ID populated inside OCELOT_SKB_CB(clone)->ts_id
> + * by ocelot_port_add_txtstamp_skb
> */
> if (ocelot_port->ptp_cmd == IFH_REW_OP_TWO_STEP_PTP)
> - rew_op |= clone->cb[0] << 3;
> + rew_op |= OCELOT_SKB_CB(clone)->ts_id << 3;
>
> ocelot_port_inject_frame(ocelot, port, 0, rew_op, skb);
>
> @@ -46,7 +46,7 @@ static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
> u16 tx_vid = dsa_8021q_tx_vid(dp->ds, dp->index);
> u16 queue_mapping = skb_get_queue_mapping(skb);
> u8 pcp = netdev_txq_to_tc(netdev, queue_mapping);
> - struct sk_buff *clone = DSA_SKB_CB(skb)->clone;
> + struct sk_buff *clone = OCELOT_SKB_CB(skb)->clone;
>
> /* TX timestamping was requested, so inject through MMIO */
> if (clone)
> --
> 2.25.1

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In reply to: Y.b. Lu: "RE: [net-next, v2, 3/7] net: dsa: free skb->cb usage in core driver"
Next in thread: Yangbo Lu: "[net-next, v2, 7/7] net: mscc: ocelot: support PTP Sync one-step timestamping"
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