Re: [B.A.T.M.A.N.] [PATCH 1/6] batman-adv: use consume_skb for non-dropped packets

On Sun, Jul 17, 2016 at 09:04:00PM +0200, Sven Eckelmann wrote:

kfree_skb assumes that an skb is dropped after an failure and notes that. consume_skb should be used in non-failure situations. Such information is important for dropmonitor netlink which tells how many packets were dropped and where this drop happened.

Just a few, curious questions regarding why a kfree_skb() was chosen instead of a consume_skb() in a few places.

Especially so that I hopefully know which one best to use when rebasing the "batman-adv: fix race conditions on interface removal" patch :-).

Signed-off-by: Sven Eckelmann sven@narfation.org

net/batman-adv/bat_iv_ogm.c | 13 ++++++++----- net/batman-adv/fragmentation.c | 20 ++++++++++++++------ net/batman-adv/network-coding.c | 24 +++++++++++++++--------- net/batman-adv/send.c | 27 +++++++++++++++++++-------- net/batman-adv/send.h | 3 ++- net/batman-adv/soft-interface.c | 2 +- 6 files changed, 59 insertions(+), 30 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c index a40cdf2..baf3d72 100644 --- a/net/batman-adv/bat_iv_ogm.c +++ b/net/batman-adv/bat_iv_ogm.c @@ -1786,8 +1787,10 @@ static void batadv_iv_send_outstanding_bat_ogm_packet(struct work_struct *work) hlist_del(&forw_packet->list); spin_unlock_bh(&bat_priv->forw_bat_list_lock);

• if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_DEACTIVATING)

• if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_DEACTIVATING) {

• dropped = true;
  

  goto out;
• }

Is this reallly a failure case?

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c index 0934730..461b77d 100644 --- a/net/batman-adv/fragmentation.c +++ b/net/batman-adv/fragmentation.c @@ -42,17 +42,23 @@ @@ -73,7 +79,7 @@ void batadv_frag_purge_orig(struct batadv_orig_node *orig_node, spin_lock_bh(&chain->lock);

if (!check_cb || check_cb(chain)) {

• 	batadv_frag_clear_chain(&chain->head);
  

• 	batadv_frag_clear_chain(&chain->head, true);
  chain->size = 0;
  

  }

Hm, have you chosen kfree_skb() over consume_skb() because it cannot easily be determined whether this call was from a failure case or not?

diff --git a/net/batman-adv/network-coding.c b/net/batman-adv/network-coding.c index 293ef4f..e924256 100644 --- a/net/batman-adv/network-coding.c +++ b/net/batman-adv/network-coding.c @@ -611,7 +617,7 @@ static bool batadv_nc_sniffed_purge(struct batadv_priv *bat_priv,

/* purge nc packet */ list_del(&nc_packet->list);

• batadv_nc_packet_free(nc_packet);

• batadv_nc_packet_free(nc_packet, true);

  res = true;

I could imagine, that with promiscious sniffing for coded packets, outdated, coded packets happen frequently and is not necessarilly a failure per se but to be expected.

On the other hand, missing a coding opportunity could have happened due to some failure elsewhere (a broken wifi driver, a noisy environment, ...).

In such an ambiguous case, should kfree_skb() be prefered over consume_skb()?

diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c index 8d4e1f5..4f44ee2 100644 --- a/net/batman-adv/send.c +++ b/net/batman-adv/send.c @@ -610,6 +616,7 @@ static void batadv_send_outstanding_bcast_packet(struct work_struct *work) struct sk_buff *skb1; struct net_device *soft_iface; struct batadv_priv *bat_priv;

• bool dropped = false;

  delayed_work = to_delayed_work(work); forw_packet = container_of(delayed_work, struct batadv_forw_packet,

@@ -621,11 +628,15 @@ static void batadv_send_outstanding_bcast_packet(struct work_struct *work) hlist_del(&forw_packet->list); spin_unlock_bh(&bat_priv->forw_bcast_list_lock);

• if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_DEACTIVATING)

• if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_DEACTIVATING) {

• dropped = true;
  

  goto out;
• }

Same as above, why is this considered a failure case?

• if (batadv_dat_drop_broadcast_packet(bat_priv, forw_packet))

• if (batadv_dat_drop_broadcast_packet(bat_priv, forw_packet)) {

• dropped = true;
  

  goto out;
• }

Why is this a failure? Isn't DAT supposed to drop things to avoid a failure case (that is duplicate broadcast packets on the client side)?

@@ -699,7 +710,7 @@ batadv_purge_outstanding_packets(struct batadv_priv *bat_priv,

if (pending) {
	hlist_del(&forw_packet->list);

• 	batadv_forw_packet_free(forw_packet);
  

• 	batadv_forw_packet_free(forw_packet, true);
  

  } } spin_unlock_bh(&bat_priv->forw_bcast_list_lock);

@@ -726,7 +737,7 @@ batadv_purge_outstanding_packets(struct batadv_priv *bat_priv,

if (pending) {
	hlist_del(&forw_packet->list);

• 	batadv_forw_packet_free(forw_packet);
  

• 	batadv_forw_packet_free(forw_packet, true);
  

  } }

These two above, again, why signaling a failure if it is a legitimate shutdown process?

Regards, Linus