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    SubjectRe: [net-next, v2, 3/7] net: dsa: free skb->cb usage in core driver
    Date
    On Mon, Apr 26, 2021 at 17:37, Yangbo Lu <yangbo.lu@nxp.com> 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@nxp.com>
    > ---
    > 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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