On Samstag, 29. Oktober 2016 04:32:40 CEST Linus Lüssing wrote:
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;- }
Is this reallly a failure case?
Hm, I would say it is not an extreme form of failure. But it is not a success either. So I've decided to use kfree_skb. The documentation is not really clear about it (or I missed the correct documentation). So this is my interpretation of it (which might be wrong).
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?
My interpretation was that batadv_frag_purge_orig means that the fragments weren't successfully assembled. So it is some kind of soft failure.
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;- }
Same as above, why is this considered a failure case?
Because it wasn't successful at fulfilling its task.
- if (batadv_dat_drop_broadcast_packet(bat_priv, forw_packet))
- if (batadv_dat_drop_broadcast_packet(bat_priv, forw_packet)) {
dropped = true;- }
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)?
Hm, good question. I think my idea behind it was that the original packet wasn't submitted.
@@ -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);@@ -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?
Because the packet was not successfully forwarded.
Kind regards, Sven