Hi Alex,

On 16/09/14 07:57, Alexander Aring wrote:
> Hi Martin,
>
> On Mon, Sep 15, 2014 at 03:09:54PM +0100, Martin Townsend wrote:
>> Currently there are a number of error paths in the lowpan_rcv function that
>> free the skb before returning, the patch simplifies the receive path by
>> ensuring that the skb is only freed from this function.
>>
>> Passing the skb from 6lowpan up to the higher layers is not a
>> function of IPHC.  By moving it out of IPHC we also remove the
>> need to support error code returns with NET_RX codes.
>> It also makes the lowpan_rcv function more extendable as we
>> can support more compression schemes.
>>
>> With the above 2 lowpan_rcv is refacored so eliminate incorrect return 
>> values.
>>
>> Signed-off-by: Martin Townsend <martin.towns...@xsilon.com>
>> ---
>>  include/net/6lowpan.h         |  4 +--
>>  net/6lowpan/iphc.c            | 74 
>> ++++++++++++++++++-------------------------
>>  net/bluetooth/6lowpan.c       | 26 +++++++++------
>>  net/ieee802154/6lowpan_rtnl.c | 55 ++++++++++++++++++++------------
>>  4 files changed, 83 insertions(+), 76 deletions(-)
>>
>> diff --git a/include/net/6lowpan.h b/include/net/6lowpan.h
>> index d184df1..450eaaf 100644
>> --- a/include/net/6lowpan.h
>> +++ b/include/net/6lowpan.h
>> @@ -374,10 +374,10 @@ lowpan_uncompress_size(const struct sk_buff *skb, u16 
>> *dgram_offset)
>>  
>>  typedef int (*skb_delivery_cb)(struct sk_buff *skb, struct net_device *dev);
>>  
>> -int lowpan_process_data(struct sk_buff *skb, struct net_device *dev,
>> +int lowpan_process_data(struct sk_buff **skb_inout, struct net_device *dev,
>>              const u8 *saddr, const u8 saddr_type, const u8 saddr_len,
>>              const u8 *daddr, const u8 daddr_type, const u8 daddr_len,
>> -            u8 iphc0, u8 iphc1, skb_delivery_cb skb_deliver);
>> +            u8 iphc0, u8 iphc1);
>>  int lowpan_header_compress(struct sk_buff *skb, struct net_device *dev,
>>                      unsigned short type, const void *_daddr,
>>                      const void *_saddr, unsigned int len);
>> diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c
>> index 142eef5..d51e8bb 100644
>> --- a/net/6lowpan/iphc.c
>> +++ b/net/6lowpan/iphc.c
>> @@ -171,37 +171,6 @@ static int uncompress_context_based_src_addr(struct 
>> sk_buff *skb,
>>      return 0;
>>  }
>>  
>> -static int skb_deliver(struct sk_buff *skb, struct ipv6hdr *hdr,
>> -                   struct net_device *dev, skb_delivery_cb deliver_skb)
>> -{
>> -    struct sk_buff *new;
>> -    int stat;
>> -
>> -    new = skb_copy_expand(skb, sizeof(struct ipv6hdr), skb_tailroom(skb),
>> -                          GFP_ATOMIC);
>> -    kfree_skb(skb);
>> -
>> -    if (!new)
>> -            return -ENOMEM;
>> -
>> -    skb_push(new, sizeof(struct ipv6hdr));
>> -    skb_reset_network_header(new);
>> -    skb_copy_to_linear_data(new, hdr, sizeof(struct ipv6hdr));
>> -
>> -    new->protocol = htons(ETH_P_IPV6);
>> -    new->pkt_type = PACKET_HOST;
>> -    new->dev = dev;
>> -
>> -    raw_dump_table(__func__, "raw skb data dump before receiving",
>> -                   new->data, new->len);
>> -
>> -    stat = deliver_skb(new, dev);
>> -
>> -    kfree_skb(new);
>> -
>> -    return stat;
>> -}
>> -
>>  /* Uncompress function for multicast destination address,
>>   * when M bit is set.
>>   */
>> @@ -332,14 +301,15 @@ err:
>>  /* TTL uncompression values */
>>  static const u8 lowpan_ttl_values[] = { 0, 1, 64, 255 };
>>  
>> -int lowpan_process_data(struct sk_buff *skb, struct net_device *dev,
>> +int lowpan_process_data(struct sk_buff **skb_inout, struct net_device *dev,
>>                      const u8 *saddr, const u8 saddr_type, const u8 
>> saddr_len,
>>                      const u8 *daddr, const u8 daddr_type, const u8 
>> daddr_len,
>> -                    u8 iphc0, u8 iphc1, skb_delivery_cb deliver_skb)
>> +                    u8 iphc0, u8 iphc1)
>>  {
>>      struct ipv6hdr hdr = {};
>>      u8 tmp, num_context = 0;
>> -    int err;
>> +    int err = -EINVAL;
>> +    struct sk_buff *skb = *skb_inout;
>>  
>>      raw_dump_table(__func__, "raw skb data dump uncompressed",
>>                     skb->data, skb->len);
>> @@ -460,7 +430,6 @@ int lowpan_process_data(struct sk_buff *skb, struct 
>> net_device *dev,
>>      /* UDP data uncompression */
>>      if (iphc0 & LOWPAN_IPHC_NH_C) {
>>              struct udphdr uh;
>> -            struct sk_buff *new;
>>  
>>              if (uncompress_udp_header(skb, &uh))
>>                      goto drop;
>> @@ -468,14 +437,15 @@ int lowpan_process_data(struct sk_buff *skb, struct 
>> net_device *dev,
>>              /* replace the compressed UDP head by the uncompressed UDP
>>               * header
>>               */
>> -            new = skb_copy_expand(skb, sizeof(struct udphdr),
>> +            skb = skb_copy_expand(skb, sizeof(struct udphdr),
>>                                    skb_tailroom(skb), GFP_ATOMIC);
>> -            kfree_skb(skb);
>> -
>> -            if (!new)
>> -                    return -ENOMEM;
>> +            if (!skb) {
>> +                    err = -ENOMEM;
>> +                    goto drop;
>> +            }
>>  
>> -            skb = new;
>> +            kfree_skb(*skb_inout);
>> +            *skb_inout = skb;
>>  
>>              skb_push(skb, sizeof(struct udphdr));
>>              skb_reset_transport_header(skb);
>> @@ -499,11 +469,27 @@ int lowpan_process_data(struct sk_buff *skb, struct 
>> net_device *dev,
>>  
>>      raw_dump_table(__func__, "raw header dump", (u8 *)&hdr, sizeof(hdr));
>>  
>> -    return skb_deliver(skb, &hdr, dev, deliver_skb);
>> +    /* Setup skb with new uncompressed IPv6 header. */
> --- snip
>
>> +    skb = skb_copy_expand(skb, sizeof(hdr), skb_tailroom(skb),
>> +                          GFP_ATOMIC);
>> +    if (!skb)
>> +            return -ENOMEM;
>> +
>> +    kfree_skb(*skb_inout);
>> +    *skb_inout = skb;
> --- snap
>
> Ignore the below one, I will only note about this... that we don't
> forget that.
>
> This code should be a generic function for increasing headroom for
> decompressing headers (IPv6, next hdr's). Still issues with
> consume_skb/kfree_skb here.
Shall I separate out the call at the end to lowpan_process_data of process_data 
to make it truely generic?  Then once we rename them we get something more 
readable in lowpan_rcv like

lowpan_prepare_skb_for_decompression
lowpan_decompress_hdr_xxx

Then it can be used by multiple decompression schemes?

By issues with consume_skb/kfree_skb are you saying that because we have 
copy_expanded it the old skb should be consumed as it's not an error?
>
>> +
>> +    skb_push(skb, sizeof(hdr));
>> +    skb_reset_network_header(skb);
>> +    skb_copy_to_linear_data(skb, &hdr, sizeof(hdr));
>> +    skb->dev = dev;
>> +
>> +    raw_dump_table(__func__, "raw skb data dump before receiving",
>> +                   skb->data, skb->len);
>> +
>> +    return 0;
>>  
>>  drop:
>> -    kfree_skb(skb);
>> -    return -EINVAL;
>> +    return err;
>>  }
>>  EXPORT_SYMBOL_GPL(lowpan_process_data);
>>  
>> diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
>> index 206b65c..a4e340e 100644
>> --- a/net/bluetooth/6lowpan.c
>> +++ b/net/bluetooth/6lowpan.c
>> @@ -215,7 +215,7 @@ static int give_skb_to_upper(struct sk_buff *skb, struct 
>> net_device *dev)
>>      return ret;
>>  }
>>  
>> -static int process_data(struct sk_buff *skb, struct net_device *netdev,
>> +static int process_data(struct sk_buff **skb_inout, struct net_device 
>> *netdev,
>>                      struct l2cap_chan *chan)
>>  {
>>      const u8 *saddr, *daddr;
>> @@ -223,6 +223,7 @@ static int process_data(struct sk_buff *skb, struct 
>> net_device *netdev,
>>      struct lowpan_dev *dev;
>>      struct lowpan_peer *peer;
>>      unsigned long flags;
>> +    struct sk_buff *skb = *skb_inout;
>>  
>>      dev = lowpan_dev(netdev);
>>  
>> @@ -245,13 +246,12 @@ static int process_data(struct sk_buff *skb, struct 
>> net_device *netdev,
>>      if (lowpan_fetch_skb_u8(skb, &iphc1))
>>              goto drop;
>>  
>> -    return lowpan_process_data(skb, netdev,
>> +    return lowpan_process_data(skb_inout, netdev,
>>                                 saddr, IEEE802154_ADDR_LONG, EUI64_ADDR_LEN,
>>                                 daddr, IEEE802154_ADDR_LONG, EUI64_ADDR_LEN,
>> -                               iphc0, iphc1, give_skb_to_upper);
>> +                               iphc0, iphc1);
>>  
>>  drop:
>> -    kfree_skb(skb);
>>      return -EINVAL;
>>  }
>>  
>> @@ -280,9 +280,6 @@ static int recv_pkt(struct sk_buff *skb, struct 
>> net_device *dev,
>>              local_skb->protocol = htons(ETH_P_IPV6);
>>              local_skb->pkt_type = PACKET_HOST;
>>  
>> -            skb_reset_network_header(local_skb);
>> -            skb_set_transport_header(local_skb, sizeof(struct ipv6hdr));
>> -
>>              if (give_skb_to_upper(local_skb, dev) != NET_RX_SUCCESS) {
>>                      kfree_skb(local_skb);
>>                      goto drop;
>> @@ -300,9 +297,20 @@ static int recv_pkt(struct sk_buff *skb, struct 
>> net_device *dev,
>>                      if (!local_skb)
>>                              goto drop;
>>  
>> -                    ret = process_data(local_skb, dev, chan);
>> -                    if (ret != NET_RX_SUCCESS)
>> +                    ret = process_data(&local_skb, dev, chan);
>> +                    if (ret < 0) {
>> +                            kfree_skb(local_skb);
>>                              goto drop;
>> +                    }
>> +
>> +                    local_skb->protocol = htons(ETH_P_IPV6);
>> +                    local_skb->pkt_type = PACKET_HOST;
>> +
>> +                    if (give_skb_to_upper(local_skb, dev)
>> +                                                    != NET_RX_SUCCESS) {
>> +                            kfree_skb(local_skb);
>> +                            goto drop;
>> +                    }
>>  
>>                      dev->stats.rx_bytes += skb->len;
>>                      dev->stats.rx_packets++;
>> diff --git a/net/ieee802154/6lowpan_rtnl.c b/net/ieee802154/6lowpan_rtnl.c
>> index 6591d27..d39dad8 100644
>> --- a/net/ieee802154/6lowpan_rtnl.c
>> +++ b/net/ieee802154/6lowpan_rtnl.c
>> @@ -164,14 +164,22 @@ static int lowpan_give_skb_to_devices(struct sk_buff 
>> *skb,
>>              }
>>      rcu_read_unlock();
>>  
>> +    if (stat < 0) {
>> +            kfree_skb(skb);
>> +            stat = NET_RX_DROP;
>> +    } else {
>> +            consume_skb(skb);
>> +    }
> This basically works now, but it confuse developers.
>
> Look how stat is initzialed.
> There is mixed errno and NET_RX_FOO handling here. Which is part of the
> complete error handling mess. And correct freeing of skb's required a
> correct error handling.
>
> The function looks now like this:
>
>         struct lowpan_dev_record *entry;
>         struct sk_buff *skb_cp;
>         int stat = NET_RX_SUCCESS;
>
>         rcu_read_lock();
>         list_for_each_entry_rcu(entry, &lowpan_devices, list)
>                 if (lowpan_dev_info(entry->ldev)->real_dev == skb->dev) {
>                         skb_cp = skb_copy(skb, GFP_ATOMIC);
>                         if (!skb_cp) {
>                                 stat = -ENOMEM;
> Simple assign stat = NET_RX_DROP.
>                                 break;
>                         }
>
>                         skb_cp->dev = entry->ldev;
>                         stat = netif_rx(skb_cp);
>                 }
>         rcu_read_unlock();          
>         
>         if (stat < 0) {
> remove brackets and check on NET_RX_DROP. or vice versa.
>                 kfree_skb(skb);
>                 stat = NET_RX_DROP;
>         } else {                
>                 consume_skb(skb);
>         }
>         return stat;
>
> Now if the list is empty we check if (stat < 0) with a NET_RX_FOO stuff,
> we should avoid that. I mean the current situation is because somebody
> mixed this stuff and that's why we have this now.
>
> Another developers look of some code (that's what I did) and see, aaah
> returning NET_RX_FOO so we can check on it, but at this situation he
> need to think a little bit more what it is the correct handline because
> there is still some errno conversion.
Ok, will change.
>
>>      return stat;
>>  }
>>  
>> -static int process_data(struct sk_buff *skb, const struct ieee802154_hdr 
>> *hdr)
>> +static int process_data(struct sk_buff **skb_inout,
>> +                    const struct ieee802154_hdr *hdr)
>>  {
>>      u8 iphc0, iphc1;
>>      struct ieee802154_addr_sa sa, da;
>>      void *sap, *dap;
>> +    struct sk_buff *skb = *skb_inout;
>>  
>>      raw_dump_table(__func__, "raw skb data dump", skb->data, skb->len);
>>      /* at least two bytes will be used for the encoding */
>> @@ -197,13 +205,11 @@ static int process_data(struct sk_buff *skb, const 
>> struct ieee802154_hdr *hdr)
>>      else
>>              dap = &da.hwaddr;
>>  
>> -    return lowpan_process_data(skb, skb->dev, sap, sa.addr_type,
>> +    return lowpan_process_data(skb_inout, skb->dev, sap, sa.addr_type,
>>                                 IEEE802154_ADDR_LEN, dap, da.addr_type,
>> -                               IEEE802154_ADDR_LEN, iphc0, iphc1,
>> -                               lowpan_give_skb_to_devices);
>> +                               IEEE802154_ADDR_LEN, iphc0, iphc1);
>>  
>>  drop:
>> -    kfree_skb(skb);
>>      return -EINVAL;
>>  }
>>  
>> @@ -478,36 +484,39 @@ static int lowpan_rcv(struct sk_buff *skb, struct 
>> net_device *dev,
>>  
>>      /* check that it's our buffer */
>>      if (skb->data[0] == LOWPAN_DISPATCH_IPV6) {
>> -            skb->protocol = htons(ETH_P_IPV6);
>> -            skb->pkt_type = PACKET_HOST;
>> -
>>              /* Pull off the 1-byte of 6lowpan header. */
>>              skb_pull(skb, 1);
>>  
>> -            ret = lowpan_give_skb_to_devices(skb, NULL);
>> -            if (ret == NET_RX_DROP)
>> -                    goto drop;
>> +            ret = NET_RX_SUCCESS;
> We don't need to set ret here.
This will all change in my future patch to refactor this function to be more 
RFC compliant.  Will send to linux-wpan once this is in.
>
>>      } else {
>>              switch (skb->data[0] & 0xe0) {
>>              case LOWPAN_DISPATCH_IPHC:      /* ipv6 datagram */
>> -                    ret = process_data(skb, &hdr);
>> -                    if (ret == NET_RX_DROP)
>> -                            goto drop;
>> +                    ret = process_data(&skb, &hdr);
>> +                    if (ret < 0)
>> +                            goto drop_skb;
>>                      break;
>>              case LOWPAN_DISPATCH_FRAG1:     /* first fragment header */
>>                      ret = lowpan_frag_rcv(skb, LOWPAN_DISPATCH_FRAG1);
>>                      if (ret == 1) {
>> -                            ret = process_data(skb, &hdr);
>> -                            if (ret == NET_RX_DROP)
>> -                                    goto drop;
>> +                            ret = process_data(&skb, &hdr);
>> +                            if (ret < 0)
>> +                                    goto drop_skb;
>> +                    } else if (ret < 0) {
>> +                            goto drop;
>> +                    } else {
>> +                            return NET_RX_SUCCESS;
>>                      }
>>                      break;
>>              case LOWPAN_DISPATCH_FRAGN:     /* next fragments headers */
>>                      ret = lowpan_frag_rcv(skb, LOWPAN_DISPATCH_FRAGN);
>>                      if (ret == 1) {
>> -                            ret = process_data(skb, &hdr);
>> -                            if (ret == NET_RX_DROP)
>> -                                    goto drop;
>> +                            ret = process_data(&skb, &hdr);
>> +                            if (ret < 0)
>> +                                    goto drop_skb;
>> +                    } else if (ret < 0) {
>> +                            goto drop;
>> +                    } else {
>> +                            return NET_RX_SUCCESS;
>>                      }
>>                      break;
>>              default:
>> @@ -515,7 +524,11 @@ static int lowpan_rcv(struct sk_buff *skb, struct 
>> net_device *dev,
>>              }
>>      }
>>  
>> -    return NET_RX_SUCCESS;
>> +    /* Pass IPv6 packet up to next layer */
>> +    skb->protocol = htons(ETH_P_IPV6);
>> +    skb->pkt_type = PACKET_HOST;
>> +    return lowpan_give_skb_to_devices(skb, NULL);
>> +
> Please ignore the above one, also a hint:
>
> Good that we have this now, so we can do a on the fly decompression when
> receiving FRAG1. This required setting skb->len here.
Are you saying that skb->len needs setting here? or just that to do on the fly 
decompression it's required?


>
> - Alex
> --
> To unsubscribe from this list: send the line "unsubscribe linux-wpan" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

I'll try and respin later today.
- Martin.

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