Currently we schedule a broadcast packet like:
3x: [ [(re-)queue] --> for(hard-if): maybe-transmit ]
The intention of queueing a broadcast packet multiple times is to increase robustness for wireless interfaces. However on interfaces which we only broadcast on once the queueing induces an unnecessary penalty. This patch restructures the queueing to be performed on a per interface basis:
for(hard-if): - transmit - if wireless: [queue] --> transmit --> [requeue] --> transmit
Next to the performance benefits on non-wireless interfaces this should also make it easier to apply alternative strategies for transmissions on wireless interfaces in the future (for instance sending via unicast transmissions on wireless interfaces, without queueing in batman-adv, if appropriate).
Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue ---
Changelog v3:
* changed all skb_clone() calls to skb_copy(), to move the skb_copy()->skb_clone() changes to extra commits with their own explanation
Changelog v2:
* fixed spelling of "unnecessary" in commit message (thanks Sven) * removed now superflous kerneldoc for hard_iface in batadv_forw_packet_bcasts_left() (thanks Sven) * removed delay check for queued (re)broadcasts in batadv_forw_bcast_packet_if(): the only case where a delay is set for this function is for a delayed, DAT fallback ARP Request from this node, then however num_bcasts will be >=1, too, and the fallback ARP Request will be scheduled anyway --- net/batman-adv/main.h | 1 - net/batman-adv/routing.c | 9 +- net/batman-adv/send.c | 374 +++++++++++++++++++++----------- net/batman-adv/send.h | 12 +- net/batman-adv/soft-interface.c | 12 +- 5 files changed, 270 insertions(+), 138 deletions(-)
diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h index 8f0102b7..baa9fcbe 100644 --- a/net/batman-adv/main.h +++ b/net/batman-adv/main.h @@ -88,7 +88,6 @@ /* number of packets to send for broadcasts on different interface types */ #define BATADV_NUM_BCASTS_DEFAULT 1 #define BATADV_NUM_BCASTS_WIRELESS 3 -#define BATADV_NUM_BCASTS_MAX 3
/* length of the single packet used by the TP meter */ #define BATADV_TP_PACKET_LEN ETH_DATA_LEN diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c index 40f5cffd..bb9e93e3 100644 --- a/net/batman-adv/routing.c +++ b/net/batman-adv/routing.c @@ -1182,9 +1182,9 @@ int batadv_recv_bcast_packet(struct sk_buff *skb, struct batadv_bcast_packet *bcast_packet; struct ethhdr *ethhdr; int hdr_size = sizeof(*bcast_packet); - int ret = NET_RX_DROP; s32 seq_diff; u32 seqno; + int ret;
/* drop packet if it has not necessary minimum size */ if (unlikely(!pskb_may_pull(skb, hdr_size))) @@ -1210,7 +1210,7 @@ int batadv_recv_bcast_packet(struct sk_buff *skb, if (batadv_is_my_mac(bat_priv, bcast_packet->orig)) goto free_skb;
- if (bcast_packet->ttl < 2) + if (bcast_packet->ttl-- < 2) goto free_skb;
orig_node = batadv_orig_hash_find(bat_priv, bcast_packet->orig); @@ -1249,7 +1249,9 @@ int batadv_recv_bcast_packet(struct sk_buff *skb, batadv_skb_set_priority(skb, sizeof(struct batadv_bcast_packet));
/* rebroadcast packet */ - batadv_add_bcast_packet_to_list(bat_priv, skb, 1, false); + ret = batadv_forw_bcast_packet(bat_priv, skb, 0, false); + if (ret == NETDEV_TX_BUSY) + goto free_skb;
/* don't hand the broadcast up if it is from an originator * from the same backbone. @@ -1275,6 +1277,7 @@ int batadv_recv_bcast_packet(struct sk_buff *skb, spin_unlock_bh(&orig_node->bcast_seqno_lock); free_skb: kfree_skb(skb); + ret = NET_RX_DROP; out: if (orig_node) batadv_orig_node_put(orig_node); diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c index 157abe92..07b0ba26 100644 --- a/net/batman-adv/send.c +++ b/net/batman-adv/send.c @@ -737,57 +737,48 @@ void batadv_forw_packet_ogmv1_queue(struct batadv_priv *bat_priv, }
/** - * batadv_add_bcast_packet_to_list() - queue broadcast packet for multiple sends + * batadv_forw_bcast_packet_to_list() - queue broadcast packet for transmissions * @bat_priv: the bat priv with all the soft interface information * @skb: broadcast packet to add * @delay: number of jiffies to wait before sending * @own_packet: true if it is a self-generated broadcast packet + * @if_in: the interface where the packet was received on + * @if_out: the outgoing interface to queue on * - * add a broadcast packet to the queue and setup timers. broadcast packets + * Adds a broadcast packet to the queue and sets up timers. Broadcast packets * are sent multiple times to increase probability for being received. * - * The skb is not consumed, so the caller should make sure that the - * skb is freed. - * * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. */ -int batadv_add_bcast_packet_to_list(struct batadv_priv *bat_priv, - const struct sk_buff *skb, - unsigned long delay, - bool own_packet) +static int batadv_forw_bcast_packet_to_list(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet, + struct batadv_hard_iface *if_in, + struct batadv_hard_iface *if_out) { - struct batadv_hard_iface *primary_if; struct batadv_forw_packet *forw_packet; - struct batadv_bcast_packet *bcast_packet; + unsigned long send_time = jiffies; struct sk_buff *newskb;
- primary_if = batadv_primary_if_get_selected(bat_priv); - if (!primary_if) - goto err; - newskb = skb_copy(skb, GFP_ATOMIC); - if (!newskb) { - batadv_hardif_put(primary_if); + if (!newskb) goto err; - }
- forw_packet = batadv_forw_packet_alloc(primary_if, NULL, + forw_packet = batadv_forw_packet_alloc(if_in, if_out, &bat_priv->bcast_queue_left, bat_priv, newskb); - batadv_hardif_put(primary_if); if (!forw_packet) goto err_packet_free;
- /* as we have a copy now, it is safe to decrease the TTL */ - bcast_packet = (struct batadv_bcast_packet *)newskb->data; - bcast_packet->ttl--; - forw_packet->own = own_packet;
INIT_DELAYED_WORK(&forw_packet->delayed_work, batadv_send_outstanding_bcast_packet);
- batadv_forw_packet_bcast_queue(bat_priv, forw_packet, jiffies + delay); + send_time += delay ? delay : msecs_to_jiffies(5); + + batadv_forw_packet_bcast_queue(bat_priv, forw_packet, send_time); return NETDEV_TX_OK;
err_packet_free: @@ -796,10 +787,220 @@ int batadv_add_bcast_packet_to_list(struct batadv_priv *bat_priv, return NETDEV_TX_BUSY; }
+/** + * batadv_forw_bcast_packet_if() - forward and queue a broadcast packet + * @bat_priv: the bat priv with all the soft interface information + * @skb: broadcast packet to add + * @delay: number of jiffies to wait before sending + * @own_packet: true if it is a self-generated broadcast packet + * @if_in: the interface where the packet was received on + * @if_out: the outgoing interface to forward to + * + * Transmits a broadcast packet on the specified interface either immediately + * or if a delay is given after that. Furthermore, queues additional + * retransmissions if this interface is a wireless one. + * + * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. + */ +static int batadv_forw_bcast_packet_if(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet, + struct batadv_hard_iface *if_in, + struct batadv_hard_iface *if_out) +{ + unsigned int num_bcasts = if_out->num_bcasts; + struct sk_buff *newskb; + int ret = NETDEV_TX_OK; + + if (!delay) { + newskb = skb_copy(skb, GFP_ATOMIC); + if (!newskb) + return NETDEV_TX_BUSY; + + batadv_send_broadcast_skb(newskb, if_out); + num_bcasts--; + } + + /* delayed broadcast or rebroadcasts? */ + if (num_bcasts >= 1) { + BATADV_SKB_CB(skb)->num_bcasts = num_bcasts; + + ret = batadv_forw_bcast_packet_to_list(bat_priv, skb, delay, + own_packet, if_in, + if_out); + } + + return ret; +} + +/** + * batadv_send_no_broadcast() - check whether (re)broadcast is necessary + * @bat_priv: the bat priv with all the soft interface information + * @skb: broadcast packet to check + * @own_packet: true if it is a self-generated broadcast packet + * @if_out: the outgoing interface checked and considered for (re)broadcast + * + * Return: False if a packet needs to be (re)broadcasted on the given interface, + * true otherwise. + */ +static bool batadv_send_no_broadcast(struct batadv_priv *bat_priv, + struct sk_buff *skb, bool own_packet, + struct batadv_hard_iface *if_out) +{ + struct batadv_hardif_neigh_node *neigh_node = NULL; + struct batadv_bcast_packet *bcast_packet; + u8 *orig_neigh; + u8 *neigh_addr; + char *type; + int ret; + + if (!own_packet) { + neigh_addr = eth_hdr(skb)->h_source; + neigh_node = batadv_hardif_neigh_get(if_out, + neigh_addr); + } + + bcast_packet = (struct batadv_bcast_packet *)skb->data; + orig_neigh = neigh_node ? neigh_node->orig : NULL; + + ret = batadv_hardif_no_broadcast(if_out, bcast_packet->orig, + orig_neigh); + + if (neigh_node) + batadv_hardif_neigh_put(neigh_node); + + /* ok, may broadcast */ + if (!ret) + return false; + + /* no broadcast */ + switch (ret) { + case BATADV_HARDIF_BCAST_NORECIPIENT: + type = "no neighbor"; + break; + case BATADV_HARDIF_BCAST_DUPFWD: + type = "single neighbor is source"; + break; + case BATADV_HARDIF_BCAST_DUPORIG: + type = "single neighbor is originator"; + break; + default: + type = "unknown"; + } + + batadv_dbg(BATADV_DBG_BATMAN, bat_priv, + "BCAST packet from orig %pM on %s suppressed: %s\n", + bcast_packet->orig, + if_out->net_dev->name, type); + + return true; +} + +/** + * __batadv_forw_bcast_packet() - forward and queue a broadcast packet + * @bat_priv: the bat priv with all the soft interface information + * @skb: broadcast packet to add + * @delay: number of jiffies to wait before sending + * @own_packet: true if it is a self-generated broadcast packet + * + * Transmits a broadcast packet either immediately or if a delay is given + * after that. Furthermore, queues additional retransmissions on wireless + * interfaces. + * + * This call clones the given skb, hence the caller needs to take into + * account that the data segment of the given skb might not be + * modifiable anymore. + * + * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. + */ +static int __batadv_forw_bcast_packet(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet) +{ + struct batadv_hard_iface *hard_iface; + struct batadv_hard_iface *primary_if; + int ret = NETDEV_TX_OK; + + primary_if = batadv_primary_if_get_selected(bat_priv); + if (!primary_if) + return NETDEV_TX_BUSY; + + rcu_read_lock(); + list_for_each_entry_rcu(hard_iface, &batadv_hardif_list, list) { + if (hard_iface->soft_iface != bat_priv->soft_iface) + continue; + + if (!kref_get_unless_zero(&hard_iface->refcount)) + continue; + + if (batadv_send_no_broadcast(bat_priv, skb, own_packet, + hard_iface)) { + batadv_hardif_put(hard_iface); + continue; + } + + ret = batadv_forw_bcast_packet_if(bat_priv, skb, delay, + own_packet, primary_if, + hard_iface); + batadv_hardif_put(hard_iface); + + if (ret == NETDEV_TX_BUSY) + break; + } + rcu_read_unlock(); + + batadv_hardif_put(primary_if); + return ret; +} + +/** + * batadv_forw_bcast_packet() - forward and queue a broadcast packet + * @bat_priv: the bat priv with all the soft interface information + * @skb: broadcast packet to add + * @delay: number of jiffies to wait before sending + * @own_packet: true if it is a self-generated broadcast packet + * + * Transmits a broadcast packet either immediately or if a delay is given + * after that. Furthermore, queues additional retransmissions on wireless + * interfaces. + * + * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. + */ +int batadv_forw_bcast_packet(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet) +{ + return __batadv_forw_bcast_packet(bat_priv, skb, delay, own_packet); +} + +/** + * batadv_send_bcast_packet() - send and queue a broadcast packet + * @bat_priv: the bat priv with all the soft interface information + * @skb: broadcast packet to add + * @delay: number of jiffies to wait before sending + * @own_packet: true if it is a self-generated broadcast packet + * + * Transmits a broadcast packet either immediately or if a delay is given + * after that. Furthermore, queues additional retransmissions on wireless + * interfaces. + * + * Consumes the provided skb. + */ +void batadv_send_bcast_packet(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet) +{ + __batadv_forw_bcast_packet(bat_priv, skb, delay, own_packet); + consume_skb(skb); +} + /** * batadv_forw_packet_bcasts_left() - check if a retransmission is necessary * @forw_packet: the forwarding packet to check - * @hard_iface: the interface to check on * * Checks whether a given packet has any (re)transmissions left on the provided * interface. @@ -811,28 +1012,20 @@ int batadv_add_bcast_packet_to_list(struct batadv_priv *bat_priv, * Return: True if (re)transmissions are left, false otherwise. */ static bool -batadv_forw_packet_bcasts_left(struct batadv_forw_packet *forw_packet, - struct batadv_hard_iface *hard_iface) +batadv_forw_packet_bcasts_left(struct batadv_forw_packet *forw_packet) { - unsigned int max; - - if (hard_iface) - max = hard_iface->num_bcasts; - else - max = BATADV_NUM_BCASTS_MAX; - - return BATADV_SKB_CB(forw_packet->skb)->num_bcasts < max; + return BATADV_SKB_CB(forw_packet->skb)->num_bcasts; }
/** - * batadv_forw_packet_bcasts_inc() - increment retransmission counter of a + * batadv_forw_packet_bcasts_dec() - decrement retransmission counter of a * packet - * @forw_packet: the packet to increase the counter for + * @forw_packet: the packet to decrease the counter for */ static void -batadv_forw_packet_bcasts_inc(struct batadv_forw_packet *forw_packet) +batadv_forw_packet_bcasts_dec(struct batadv_forw_packet *forw_packet) { - BATADV_SKB_CB(forw_packet->skb)->num_bcasts++; + BATADV_SKB_CB(forw_packet->skb)->num_bcasts--; }
/** @@ -843,30 +1036,30 @@ batadv_forw_packet_bcasts_inc(struct batadv_forw_packet *forw_packet) */ bool batadv_forw_packet_is_rebroadcast(struct batadv_forw_packet *forw_packet) { - return BATADV_SKB_CB(forw_packet->skb)->num_bcasts > 0; + unsigned char num_bcasts = BATADV_SKB_CB(forw_packet->skb)->num_bcasts; + + return num_bcasts != forw_packet->if_outgoing->num_bcasts; }
+/** + * batadv_send_outstanding_bcast_packet() - transmit a queued broadcast packet + * @work: work queue item + * + * Transmits a queued broadcast packet and if necessary reschedules it. + */ static void batadv_send_outstanding_bcast_packet(struct work_struct *work) { - struct batadv_hard_iface *hard_iface; - struct batadv_hardif_neigh_node *neigh_node; + unsigned long send_time = jiffies + msecs_to_jiffies(5); + struct batadv_forw_packet *forw_packet; struct delayed_work *delayed_work; - struct batadv_forw_packet *forw_packet; - struct batadv_bcast_packet *bcast_packet; + struct batadv_priv *bat_priv; struct sk_buff *skb1; - struct net_device *soft_iface; - struct batadv_priv *bat_priv; - unsigned long send_time = jiffies + msecs_to_jiffies(5); bool dropped = false; - u8 *neigh_addr; - u8 *orig_neigh; - int ret = 0;
delayed_work = to_delayed_work(work); forw_packet = container_of(delayed_work, struct batadv_forw_packet, delayed_work); - soft_iface = forw_packet->if_incoming->soft_iface; - bat_priv = netdev_priv(soft_iface); + bat_priv = netdev_priv(forw_packet->if_incoming->soft_iface);
if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_DEACTIVATING) { dropped = true; @@ -878,76 +1071,15 @@ static void batadv_send_outstanding_bcast_packet(struct work_struct *work) goto out; }
- bcast_packet = (struct batadv_bcast_packet *)forw_packet->skb->data; + /* send a copy of the saved skb */ + skb1 = skb_copy(forw_packet->skb, GFP_ATOMIC); + if (!skb1) + goto out;
- /* rebroadcast packet */ - rcu_read_lock(); - list_for_each_entry_rcu(hard_iface, &batadv_hardif_list, list) { - if (hard_iface->soft_iface != soft_iface) - continue; + batadv_send_broadcast_skb(skb1, forw_packet->if_outgoing); + batadv_forw_packet_bcasts_dec(forw_packet);
- if (!batadv_forw_packet_bcasts_left(forw_packet, hard_iface)) - continue; - - if (forw_packet->own) { - neigh_node = NULL; - } else { - neigh_addr = eth_hdr(forw_packet->skb)->h_source; - neigh_node = batadv_hardif_neigh_get(hard_iface, - neigh_addr); - } - - orig_neigh = neigh_node ? neigh_node->orig : NULL; - - ret = batadv_hardif_no_broadcast(hard_iface, bcast_packet->orig, - orig_neigh); - - if (ret) { - char *type; - - switch (ret) { - case BATADV_HARDIF_BCAST_NORECIPIENT: - type = "no neighbor"; - break; - case BATADV_HARDIF_BCAST_DUPFWD: - type = "single neighbor is source"; - break; - case BATADV_HARDIF_BCAST_DUPORIG: - type = "single neighbor is originator"; - break; - default: - type = "unknown"; - } - - batadv_dbg(BATADV_DBG_BATMAN, bat_priv, "BCAST packet from orig %pM on %s suppressed: %s\n", - bcast_packet->orig, - hard_iface->net_dev->name, type); - - if (neigh_node) - batadv_hardif_neigh_put(neigh_node); - - continue; - } - - if (neigh_node) - batadv_hardif_neigh_put(neigh_node); - - if (!kref_get_unless_zero(&hard_iface->refcount)) - continue; - - /* send a copy of the saved skb */ - skb1 = skb_clone(forw_packet->skb, GFP_ATOMIC); - if (skb1) - batadv_send_broadcast_skb(skb1, hard_iface); - - batadv_hardif_put(hard_iface); - } - rcu_read_unlock(); - - batadv_forw_packet_bcasts_inc(forw_packet); - - /* if we still have some more bcasts to send */ - if (batadv_forw_packet_bcasts_left(forw_packet, NULL)) { + if (batadv_forw_packet_bcasts_left(forw_packet)) { batadv_forw_packet_bcast_queue(bat_priv, forw_packet, send_time); return; diff --git a/net/batman-adv/send.h b/net/batman-adv/send.h index 2b0daf8b..08af251b 100644 --- a/net/batman-adv/send.h +++ b/net/batman-adv/send.h @@ -39,10 +39,14 @@ int batadv_send_broadcast_skb(struct sk_buff *skb, struct batadv_hard_iface *hard_iface); int batadv_send_unicast_skb(struct sk_buff *skb, struct batadv_neigh_node *neigh_node); -int batadv_add_bcast_packet_to_list(struct batadv_priv *bat_priv, - const struct sk_buff *skb, - unsigned long delay, - bool own_packet); +int batadv_forw_bcast_packet(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet); +void batadv_send_bcast_packet(struct batadv_priv *bat_priv, + struct sk_buff *skb, + unsigned long delay, + bool own_packet); void batadv_purge_outstanding_packets(struct batadv_priv *bat_priv, const struct batadv_hard_iface *hard_iface); diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c index 6b8181bc..a21884c0 100644 --- a/net/batman-adv/soft-interface.c +++ b/net/batman-adv/soft-interface.c @@ -191,7 +191,7 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb, struct vlan_ethhdr *vhdr; unsigned int header_len = 0; int data_len = skb->len, ret; - unsigned long brd_delay = 1; + unsigned long brd_delay = 0; bool do_bcast = false, client_added; unsigned short vid; u32 seqno; @@ -330,7 +330,7 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
bcast_packet = (struct batadv_bcast_packet *)skb->data; bcast_packet->version = BATADV_COMPAT_VERSION; - bcast_packet->ttl = BATADV_TTL; + bcast_packet->ttl = BATADV_TTL - 1;
/* batman packet type: broadcast */ bcast_packet->packet_type = BATADV_BCAST; @@ -346,13 +346,7 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb, seqno = atomic_inc_return(&bat_priv->bcast_seqno); bcast_packet->seqno = htonl(seqno);
- batadv_add_bcast_packet_to_list(bat_priv, skb, brd_delay, true); - - /* a copy is stored in the bcast list, therefore removing - * the original skb. - */ - consume_skb(skb); - + batadv_send_bcast_packet(bat_priv, skb, brd_delay, true); /* unicast packet */ } else { /* DHCP packets going to a server will use the GW feature */
Broadcast packets send via batadv_send_outstanding_bcast_packet() were originally copied in batadv_forw_bcast_packet_to_list() before being queued. And after that only the ethernet header will be pushed through batadv_send_broadcast_skb()->batadv_send_skb_packet() which works safely on skb clones as it uses batadv_skb_head_push()->skb_cow_head().
Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue ---
Changelog v3:
* newly added this patch, to move skb_copy()->skb_clone() change from PATCH 01/03 to a separate patch with its own explanation
net/batman-adv/send.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c index 07b0ba26..0b9dd29d 100644 --- a/net/batman-adv/send.c +++ b/net/batman-adv/send.c @@ -1072,7 +1072,7 @@ static void batadv_send_outstanding_bcast_packet(struct work_struct *work) }
/* send a copy of the saved skb */ - skb1 = skb_copy(forw_packet->skb, GFP_ATOMIC); + skb1 = skb_clone(forw_packet->skb, GFP_ATOMIC); if (!skb1) goto out;
We currently have two code paths for broadcast packets: A) self-generated, via batadv_interface_tx()->batadv_send_bcast_packet(). Or B) received/forwarded, via batadv_recv_bcast_packet()-> batadv_forw_bcast_packet().
For A), self-generated broadcast packets the only modifications to the skb data is the ethernet header which is added/pushed to the skb in batadv_send_broadcast_skb()->batadv_send_skb_packet(). However before doing so batadv_skb_head_push() is called which calls skb_cow_head() to unshare the space for the to be pushed ethernet header. So for this case, it is safe to use skb clones.
For B), received/forwarded packets the same applies as in A) for the to be forwarded packets. Only the ethernet header is added. However after (queueing for) forwarding the packet in batadv_recv_bcast_packet()->batadv_forw_bcast_packet() a packet is additionally decapsulated and is sent up the stack through batadv_recv_bcast_packet()->batadv_interface_rx(). Which needs an unshared skb data for potential modifications from other protocols. To be able to use skb clones for (re)broadcasted batman-adv broadcast packets while still ensuring that interface_rx() has a freely writeable skb we use skb_cow() to avoid sharing skb data with the skb clones in the forwarding calls.
Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue ---
Changelog v3:
* newly added this patch, to move skb_copy()->skb_clone() changes from PATCH 01/03 to a separate patch with its own explanation
net/batman-adv/send.c | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-)
diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c index 0b9dd29d..1db6b217 100644 --- a/net/batman-adv/send.c +++ b/net/batman-adv/send.c @@ -748,6 +748,10 @@ void batadv_forw_packet_ogmv1_queue(struct batadv_priv *bat_priv, * Adds a broadcast packet to the queue and sets up timers. Broadcast packets * are sent multiple times to increase probability for being received. * + * This call clones the given skb, hence the caller needs to take into + * account that the data segment of the original skb might not be + * modifiable anymore. + * * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. */ static int batadv_forw_bcast_packet_to_list(struct batadv_priv *bat_priv, @@ -761,7 +765,7 @@ static int batadv_forw_bcast_packet_to_list(struct batadv_priv *bat_priv, unsigned long send_time = jiffies; struct sk_buff *newskb;
- newskb = skb_copy(skb, GFP_ATOMIC); + newskb = skb_clone(skb, GFP_ATOMIC); if (!newskb) goto err;
@@ -800,6 +804,10 @@ static int batadv_forw_bcast_packet_to_list(struct batadv_priv *bat_priv, * or if a delay is given after that. Furthermore, queues additional * retransmissions if this interface is a wireless one. * + * This call clones the given skb, hence the caller needs to take into + * account that the data segment of the original skb might not be + * modifiable anymore. + * * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. */ static int batadv_forw_bcast_packet_if(struct batadv_priv *bat_priv, @@ -814,7 +822,7 @@ static int batadv_forw_bcast_packet_if(struct batadv_priv *bat_priv, int ret = NETDEV_TX_OK;
if (!delay) { - newskb = skb_copy(skb, GFP_ATOMIC); + newskb = skb_clone(skb, GFP_ATOMIC); if (!newskb) return NETDEV_TX_BUSY;
@@ -966,6 +974,8 @@ static int __batadv_forw_bcast_packet(struct batadv_priv *bat_priv, * after that. Furthermore, queues additional retransmissions on wireless * interfaces. * + * This call might reallocate skb data. + * * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY on errors. */ int batadv_forw_bcast_packet(struct batadv_priv *bat_priv, @@ -973,7 +983,15 @@ int batadv_forw_bcast_packet(struct batadv_priv *bat_priv, unsigned long delay, bool own_packet) { - return __batadv_forw_bcast_packet(bat_priv, skb, delay, own_packet); + int ret = __batadv_forw_bcast_packet(bat_priv, skb, delay, own_packet); + + if (ret == NETDEV_TX_BUSY) + return ret; + + /* __batadv_forw_bcast_packet clones, make sure original + * skb stays writeable + */ + return (skb_cow(skb, 0) < 0) ? NETDEV_TX_BUSY : NETDEV_TX_OK; }
/**
On Monday, 17 May 2021 00:33:09 CEST Linus Lüssing wrote: [...]
However after (queueing for) forwarding the packet in batadv_recv_bcast_packet()->batadv_forw_bcast_packet() a packet is additionally decapsulated and is sent up the stack through batadv_recv_bcast_packet()->batadv_interface_rx(). Which needs an unshared skb data for potential modifications from other protocols. To be able to use skb clones for (re)broadcasted batman-adv broadcast packets while still ensuring that interface_rx() has a freely writeable skb we use skb_cow() to avoid sharing skb data with the skb clones in
So you are talking here about netif_rx. But this doesn't seem to ensure that the data is "private" at all. It can even easily happen that there is a tcpdump listening at the same time on the interface which is "netif_rx"ing. In this case, both AF_PACKET and whatever is parsing the layer 3 stuff is receiving an skb_shared() skb.
In this case, the receiver of the skb must use skb_share_check to clone the skb - so we would end up with the same situation as you had before your skb_cow. And it must then for example use skb_cow_data to "gain" write access to the skb's data.
Take for example the bridge code. You can find the skb_share_check in br_handle_frame. Afterwards, it knows that it has a clone of the skb (but not necessarily a private copy of the actual data). If it needs to modify the data then it is copying the skb.
Another example is the IPv4 code. One of the first things it does is to check in ip_rcv_core for the shared skb. And if it needs to modify it (for example by forwarding it in ip_forward), it uses skb_cow directly.
Kind regards, Sven
On Monday, 17 May 2021 00:33:09 CEST Linus Lüssing wrote:
/* __batadv_forw_bcast_packet clones, make sure original* skb stays writeable*/return (skb_cow(skb, 0) < 0) ? NETDEV_TX_BUSY : NETDEV_TX_OK;
Just because we had this discussion a couple of hours ago: My last comment from May was that the skb_cow might be unnecessary - not that you need a skb_copy.
You wrote (for situation B):
a packet is additionally decapsulated and is sent up the stack through batadv_recv_bcast_packet()->batadv_interface_rx(). Which needs an unshared skb data for potential modifications from other protocols.
And my reply to this was:
Take for example the bridge code. You can find the skb_share_check in br_handle_frame. Afterwards, it knows that it has a clone of the skb (but not necessarily a private copy of the actual data). If it needs to modify the data then it is copying the skb.
Another example is the IPv4 code. One of the first things it does is to check in ip_rcv_core for the shared skb. And if it needs to modify it (for example by forwarding it in ip_forward), it uses skb_cow directly.
Kind regards, Sven
b.a.t.m.a.n@lists.open-mesh.org
-
Linus Lüssing -
Sven Eckelmann