Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Reorganize sequence number handling

Linus Lüssing
2010-04-06T09:33:31Z

Hi Simon,

sorry, I need to resign my ack again, I guess. I now noticed that
I couldn't reproduce the issue anymore because of not being able
to produce enough broadcasts (~3x83 small packets per second).
It turned out, that the ping utility itself seems to limit the
interval when it gets no icmp reply although flood-ping is
activated. So with setting "/proc/sys/net/ipv4/icmp_echo_ignore_broadcasts"
to 0 on the host which produces the icmp requests, I could produce
~7000 packets per second again - the ping utilitly seems to use
the icmp replies as a flow control, I guess.

And then the issue seems to still be there here. I start the
broadcast-flood-ping in a setup A - B - C on node A and stop it
again on node A a second later. Then the icmp-packets still
bounce between B and C until B stops with no more memory available
(haven't applied your 2nd patch for limiting the queue yet).

From your original patch, I'm getting only one "XXX protected it messages" on A and C,
but a lot more on B:
[ 416.612253] XXX protect it!
[ 446.618569] XXX protect it!
[ 476.824103] XXX protect it!
[ 506.836694] XXX protect it!
[ 537.036869] XXX protect it!
[ 567.056133] XXX protect it!
[ 597.058637] XXX protect it!
[ 847.936099] XXX protect it!
[ 848.560450] XXX protect it!
[ 907.686827] XXX protect it!
[ 1994.836111] XXX protect it!

Cheers, Linus

On Mon, Apr 05, 2010 at 12:01:20AM +0200, Simon Wunderlich wrote:
> BATMAN and broadcast packets are tracked with a sequence number window of
> currently 64 entries to measure and avoid duplicates. Packets which have a
> sequence number smaller than the newest received packet minus 64 are not
> within this sequence number window anymore and are called "old packets" from
> now on.
>
> When old packets are received, the routing code assumes that the host of the
> originator has been restarted. This assumption however might be wrong as
> packets can also be delayed by NIC drivers, e.g. because of long queues or
> collision detection in dense WiFi environments. This behaviour can be
> reproduced by doing a broadcast ping flood in a dense node environment.
>
> The effect is that the sequence number window is jumping forth and back,
> accepting and forwarding any packet (because packets are assumed to be "new")
> and causing loops.
>
> To overcome this problem, the sequence number handling has been reorganized.
> When an old packet is received, the window is reset back only once. Other old
> packets are dropped for (currently) 30 seconds to "protect" the new sequence
> number and avoid the hopping as described above.
>
> The reorganization brings some code cleanups (at least i hope you feel the
> same) and also fixes a bug in count_real_packets() which falsely updated
> the last_real_seqno for slightly older packets within the seqno window
> if they are no duplicates.
>
> Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
> Acked-by: Linus Luessing <linus.luessing@web.de>
>
> Index: a/batman-adv-kernelland/types.h
> ===================================================================
> --- a/batman-adv-kernelland/types.h (revision 1616)
> +++ a/batman-adv-kernelland/types.h (working copy)
> @@ -55,6 +55,10 @@
> uint8_t tq_own;
> int tq_asym_penalty;
> unsigned long last_valid; /* when last packet from this node was received */
> + unsigned long bcast_seqno_reset; /* time when the broadcast
> + seqno window was reset. */
> + unsigned long batman_seqno_reset;/* time when the batman seqno
> + window was reset. */
> uint8_t gw_flags; /* flags related to gateway class */
> uint8_t flags; /* for now only VIS_SERVER flag. */
> unsigned char *hna_buff;
> Index: a/batman-adv-kernelland/bitarray.c
> ===================================================================
> --- a/batman-adv-kernelland/bitarray.c (revision 1616)
> +++ a/batman-adv-kernelland/bitarray.c (working copy)
> @@ -111,48 +111,74 @@
> seq_bits[i] = 0;
> }
>
> +static void bit_reset_window(TYPE_OF_WORD *seq_bits)
> +{
> + int i;
> + for (i = 0; i < NUM_WORDS; i++)
> + seq_bits[i] = 0;
> +}
>
> -/* receive and process one packet, returns 1 if received seq_num is considered
> - * new, 0 if old */
> +
> +/* receive and process one packet within the sequence number window.
> + *
> + * returns:
> + * 1 if the window was moved (either new or very old)
> + * 0 if the window was not moved/shifted.
> + */
> char bit_get_packet(TYPE_OF_WORD *seq_bits, int16_t seq_num_diff,
> int8_t set_mark)
> {
> - int i;
> + /* sequence number is slightly older. We already got a sequence number
> + * higher than this one, so we just mark it. */
>
> - /* we already got a sequence number higher than this one, so we just
> - * mark it. this should wrap around the integer just fine */
> if ((seq_num_diff < 0) && (seq_num_diff >= -TQ_LOCAL_WINDOW_SIZE)) {
> if (set_mark)
> bit_mark(seq_bits, -seq_num_diff);
> return 0;
> }
>
> - /* it seems we missed a lot of packets or the other host restarted */
> - if ((seq_num_diff > TQ_LOCAL_WINDOW_SIZE) ||
> - (seq_num_diff < -TQ_LOCAL_WINDOW_SIZE)) {
> + /* sequence number is slightly newer, so we shift the window and
> + * set the mark if required */
>
> - if (seq_num_diff > TQ_LOCAL_WINDOW_SIZE)
> - bat_dbg(DBG_BATMAN,
> - "We missed a lot of packets (%i) !\n",
> - seq_num_diff-1);
> + if ((seq_num_diff >= 0) && (seq_num_diff <= TQ_LOCAL_WINDOW_SIZE)) {
> + bit_shift(seq_bits, seq_num_diff);
>
> - if (-seq_num_diff > TQ_LOCAL_WINDOW_SIZE)
> - bat_dbg(DBG_BATMAN,
> - "Other host probably restarted !\n");
> + if (set_mark)
> + bit_mark(seq_bits, 0);
> + return 1;
> + }
>
> - for (i = 0; i < NUM_WORDS; i++)
> - seq_bits[i] = 0;
> + /* sequence number is much newer, probably missed a lot of packets */
>
> + if (seq_num_diff > TQ_LOCAL_WINDOW_SIZE) {
> + bat_dbg(DBG_BATMAN,
> + "We missed a lot of packets (%i) !\n",
> + seq_num_diff - 1);
> + bit_reset_window(seq_bits);
> if (set_mark)
> - seq_bits[0] = 1; /* we only have the latest packet */
> - } else {
> - bit_shift(seq_bits, seq_num_diff);
> + bit_mark(seq_bits, 0);
> + return 1;
> + }
>
> + /* received a much older packet. The other host either restarted
> + * or the old packet got delayed somewhere in the network. The
> + * packet should be dropped without calling this function if the
> + * seqno window is protected. */
> +
> + if (-seq_num_diff > TQ_LOCAL_WINDOW_SIZE) {
> +
> + bat_dbg(DBG_BATMAN,
> + "Other host probably restarted!\n");
> +
> + bit_reset_window(seq_bits);
> if (set_mark)
> bit_mark(seq_bits, 0);
> +
> + return 1;
> }
>
> - return 1;
> + /* never reached */
> + return 0;
> }
>
> /* count the hamming weight, how many good packets did we receive? just count
> Index: a/batman-adv-kernelland/originator.c
> ===================================================================
> --- a/batman-adv-kernelland/originator.c (revision 1616)
> +++ a/batman-adv-kernelland/originator.c (working copy)
> @@ -141,6 +141,8 @@
> orig_node->router = NULL;
> orig_node->batman_if = NULL;
> orig_node->hna_buff = NULL;
> + orig_node->bcast_seqno_reset = jiffies;
> + orig_node->batman_seqno_reset = jiffies;
>
> size = num_ifs * sizeof(TYPE_OF_WORD) * NUM_WORDS;
>
> Index: a/batman-adv-kernelland/routing.c
> ===================================================================
> --- a/batman-adv-kernelland/routing.c (revision 1616)
> +++ a/batman-adv-kernelland/routing.c (working copy)
> @@ -323,6 +323,37 @@
> gw_check_election(bat_priv, orig_node);
> }
>
> +/* checks whether the host restarted and is in the protection time.
> + * returns:
> + * 0 if the packet is to be accepted
> + * 1 if the packet is to be ignored.
> + */
> +static int window_protected(int16_t seq_num_diff,
> + unsigned long *last_reset)
> +{
> + if (-seq_num_diff > TQ_LOCAL_WINDOW_SIZE) {
> + if (time_after(jiffies, *last_reset +
> + msecs_to_jiffies(RESET_PROTECTION_MS))) {
> +
> + *last_reset = jiffies;
> + bat_dbg(DBG_BATMAN,
> + "old packet received, start protection\n");
> +
> + return 0;
> + } else
> + return 1;
> + }
> + return 0;
> +}
> +
> +/* processes a batman packet for all interfaces, adjusts the sequence number and
> + * finds out whether it is a duplicate.
> + * returns:
> + * 1 the packet is a duplicate
> + * 0 the packet has not yet been received
> + * -1 the packet is old and has been received while the seqno window
> + * was protected. Caller should drop it.
> + */
> static char count_real_packets(struct ethhdr *ethhdr,
> struct batman_packet *batman_packet,
> struct batman_if *if_incoming)
> @@ -330,31 +361,41 @@
> struct orig_node *orig_node;
> struct neigh_node *tmp_neigh_node;
> char is_duplicate = 0;
> - uint16_t seq_diff;
> + int16_t seq_diff;
> + int need_update = 0;
> + int set_mark;
>
> orig_node = get_orig_node(batman_packet->orig);
> if (orig_node == NULL)
> return 0;
>
> + seq_diff = batman_packet->seqno - orig_node->last_real_seqno;
> +
> + /* signalize caller that the packet is to be dropped. */
> + if (window_protected(seq_diff, &orig_node->batman_seqno_reset))
> + return -1;
> +
> list_for_each_entry(tmp_neigh_node, &orig_node->neigh_list, list) {
>
> - if (!is_duplicate)
> - is_duplicate =
> - get_bit_status(tmp_neigh_node->real_bits,
> + is_duplicate |= get_bit_status(tmp_neigh_node->real_bits,
> orig_node->last_real_seqno,
> batman_packet->seqno);
> - seq_diff = batman_packet->seqno - orig_node->last_real_seqno;
> +
> if (compare_orig(tmp_neigh_node->addr, ethhdr->h_source) &&
> (tmp_neigh_node->if_incoming == if_incoming))
> - bit_get_packet(tmp_neigh_node->real_bits, seq_diff, 1);
> + set_mark = 1;
> else
> - bit_get_packet(tmp_neigh_node->real_bits, seq_diff, 0);
> + set_mark = 0;
>
> + /* if the window moved, set the update flag. */
> + need_update |= bit_get_packet(tmp_neigh_node->real_bits,
> + seq_diff, set_mark);
> +
> tmp_neigh_node->real_packet_count =
> bit_packet_count(tmp_neigh_node->real_bits);
> }
>
> - if (!is_duplicate) {
> + if (need_update) {
> bat_dbg(DBG_BATMAN, "updating last_seqno: old %d, new %d\n",
> orig_node->last_real_seqno, batman_packet->seqno);
> orig_node->last_real_seqno = batman_packet->seqno;
> @@ -587,24 +628,27 @@
> return;
> }
>
> - if (batman_packet->tq == 0) {
> - count_real_packets(ethhdr, batman_packet, if_incoming);
> -
> - bat_dbg(DBG_BATMAN, "Drop packet: originator packet with tq equal 0\n");
> - return;
> - }
> -
> if (is_my_oldorig) {
> bat_dbg(DBG_BATMAN, "Drop packet: ignoring all rebroadcast echos (sender: %pM)\n", ethhdr->h_source);
> return;
> }
>
> - is_duplicate = count_real_packets(ethhdr, batman_packet, if_incoming);
> -
> orig_node = get_orig_node(batman_packet->orig);
> if (orig_node == NULL)
> return;
>
> + is_duplicate = count_real_packets(ethhdr, batman_packet, if_incoming);
> +
> + if (is_duplicate == -1) {
> + bat_dbg(DBG_BATMAN, "Drop packet: packet within seqno protection time (sender: %pM)\n", ethhdr->h_source);
> + return;
> + }
> +
> + if (batman_packet->tq == 0) {
> + bat_dbg(DBG_BATMAN, "Drop packet: originator packet with tq equal 0\n");
> + return;
> + }
> +
> /* avoid temporary routing loops */
> if ((orig_node->router) &&
> (orig_node->router->orig_node->router) &&
> @@ -1088,6 +1132,7 @@
> struct bcast_packet *bcast_packet;
> struct ethhdr *ethhdr;
> int hdr_size = sizeof(struct bcast_packet);
> + int16_t seq_diff;
> unsigned long flags;
>
> /* drop packet if it has not necessary minimum size */
> @@ -1123,7 +1168,7 @@
> return NET_RX_DROP;
> }
>
> - /* check flood history */
> + /* check whether the packet is a duplicate */
> if (get_bit_status(orig_node->bcast_bits,
> orig_node->last_bcast_seqno,
> ntohs(bcast_packet->seqno))) {
> @@ -1131,14 +1176,20 @@
> return NET_RX_DROP;
> }
>
> - /* mark broadcast in flood history */
> - if (bit_get_packet(orig_node->bcast_bits,
> - ntohs(bcast_packet->seqno) -
> - orig_node->last_bcast_seqno, 1))
> + seq_diff = ntohs(bcast_packet->seqno) - orig_node->last_bcast_seqno;
> +
> + /* check whether the packet is old and the host just restarted. */
> + if (window_protected(seq_diff, &orig_node->bcast_seqno_reset)) {
> + spin_unlock_irqrestore(&orig_hash_lock, flags);
> + return NET_RX_DROP;
> + }
> +
> + /* mark broadcast in flood history, update window position
> + * if required. */
> + if (bit_get_packet(orig_node->bcast_bits, seq_diff, 1))
> orig_node->last_bcast_seqno = ntohs(bcast_packet->seqno);
>
> spin_unlock_irqrestore(&orig_hash_lock, flags);
> -
> /* rebroadcast packet */
> add_bcast_packet_to_list(skb);
>
> Index: a/batman-adv-kernelland/main.h
> ===================================================================
> --- a/batman-adv-kernelland/main.h (revision 1616)
> +++ a/batman-adv-kernelland/main.h (working copy)
> @@ -66,6 +66,9 @@
> * forw_packet->direct_link_flags */
> #define MAX_AGGREGATION_MS 100
>
> +#define RESET_PROTECTION_MS 30000
> +/* don't reset again within 30 seconds */
> +
> #define MODULE_INACTIVE 0
> #define MODULE_ACTIVE 1
> #define MODULE_DEACTIVATING 2
>