On Tue, Sep 16, 2014 at 09:28:10AM +0100, Martin Townsend wrote:
> 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.townsend@xxxxxxxxxx>
> >> ---
> >> 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?
yes something like that, I only see this right now. We need such
function always if we decompressing any header. We can't be sure we have
the reserved space room. I think maybe we can check before if we have
reserved room for that, if we have it then not doing a skb_copy_expand
here. If we don't have it make a skb_copy_expand here. Will speedup a
little bit in hotpath.
To check reserved headroom is faster then always do some heap
allocation.
>
> 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?
Yes, but this doesn't matter on using the stack. You only see it while
debug with ftrace [0]. [1] shows consume_skb and [2] shows kfree_skb.
If you compare it you can see it's the same but another trace call to
indicate that's an error.
There are too many issues because of them, make this is in a separate
patch. All branches seems to have this issue net/6lowpan,
net/ieee802154/6lowpan... and net/bluetooth/6lowpan...
What I mean is, it's not required to handle a correct freeing of skb.
(And you working right now on this issue, that's because we need a new
patch for this). But it's very useful and confuse users while debugging.
> >
> >> +
> >> + 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.
> >
yes, but that was not there before? I don't see that we use ret after
this branch anymore. "return lowpan_give_skb_to_devices(skb, NULL);"
only.
> >> } 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?
>
I basically talk with myself or to make a global hint. We already talk
about the on the fly decompression when receiving FRAG1 and also that we
don't need any compression when uncompressed header size(s) is greater than
FRAG1.
You told me that you want to insert the GHC ICMPv6 compression and that
makes me currently stomach ache, because there is currently the ugly
workaround solution to calculate the uncompressed header size. [3]
We need another solution for that otherwise you need to add special
handling for ICMPv6 GHC nextheader calculation also for this function
[3] and we should to avoid that. I mean it's currently a workaround, we
should make it right.
We should surely avoid to make any special handling for next header
compression which is outside for the next header compression
framework/layer. Don't know, but I can imagine you have already patches
for that. :-)
- Alex
[0] https://www.kernel.org/doc/Documentation/trace/ftrace.txt
[1] http://lxr.free-electrons.com/source/net/core/skbuff.c#L671
[2] http://lxr.free-electrons.com/source/net/core/skbuff.c#L619
[3] http://lxr.free-electrons.com/source/include/net/6lowpan.h#L360
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