Commit 5c3fbb6a authored by Gerrit Renker's avatar Gerrit Renker Committed by Arnaldo Carvalho de Melo
Browse files

[DCCP] ccid3: Fix bug in calculation of send rate 



The main object of this patch is the following bug:
 ==> In ccid3_hc_tx_packet_recv, the parameters p and X_recv were updated
     _after_ the send rate was calculated. This is clearly an error and is
     resolved by re-ordering statements.

In addition,
  * r_sample is converted from u32 to long to check whether the time difference
    was negative (it would otherwise be converted to a large u32 value)
  * protection against RTT=0 (this is possible) is provided in a further patch
  * t_elapsed is also converted to long, to match the type of r_sample
  * adds a a more debugging information regarding current send rates
  * various trivial comment/documentation updates

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
parent 76d12777

net/dccp/ccids/ccid3.c

+52 −37
Original line number Diff line number Diff line
@@ -121,12 +121,15 @@ static inline void ccid3_update_send_time(struct ccid3_hc_tx_sock *hctx) 
/*

 * Update X by

 *    If (p > 0)

 *       x_calc = calcX(s, R, p);

 *       X_calc = calcX(s, R, p);

 *       X = max(min(X_calc, 2 * X_recv), s / t_mbi);

 *    Else

 *       If (now - tld >= R)

 *          X = max(min(2 * X, 2 * X_recv), s / R);

 *          tld = now;

 *

 * If X has changed, we also update the scheduled send time t_now,

 * the inter-packet interval t_ipi, and the delta value.

 */ 

static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now)
@@ -413,10 +416,8 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
	struct dccp_tx_hist_entry *packet;

	struct timeval now;

	unsigned long t_nfb;

	u32 t_elapsed;

	u32 pinv;

	u32 x_recv;

	u32 r_sample;

	long r_sample, t_elapsed;



	BUG_ON(hctx == NULL);
@@ -427,31 +428,51 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 


	opt_recv = &hctx->ccid3hctx_options_received;



	t_elapsed = dp->dccps_options_received.dccpor_elapsed_time * 10;

	x_recv = opt_recv->ccid3or_receive_rate;

	pinv = opt_recv->ccid3or_loss_event_rate;



	switch (hctx->ccid3hctx_state) {

	case TFRC_SSTATE_NO_FBACK:

	case TFRC_SSTATE_FBACK:

		/* Calculate new round trip sample by

		 * R_sample = (now - t_recvdata) - t_delay */

		/* get t_recvdata from history */

		/* get packet from history to look up t_recvdata */

		packet = dccp_tx_hist_find_entry(&hctx->ccid3hctx_hist,

						 DCCP_SKB_CB(skb)->dccpd_ack_seq);

		if (unlikely(packet == NULL)) {

			DCCP_WARN("%s, sk=%p, seqno %llu(%s) does't exist "

			DCCP_WARN("%s(%p), seqno %llu(%s) doesn't exist "

				  "in history!\n",  dccp_role(sk), sk,

			    (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq,

				  dccp_packet_name(DCCP_SKB_CB(skb)->dccpd_type));

			return;

		}



		/* Update RTT */

		/* Update receive rate */

		hctx->ccid3hctx_x_recv = opt_recv->ccid3or_receive_rate;



		/* Update loss event rate */

		pinv = opt_recv->ccid3or_loss_event_rate;

		if (pinv == ~0U || pinv == 0)

			hctx->ccid3hctx_p = 0;

		else {

			hctx->ccid3hctx_p = 1000000 / pinv;



			if (hctx->ccid3hctx_p < TFRC_SMALLEST_P) {

				hctx->ccid3hctx_p = TFRC_SMALLEST_P;

				ccid3_pr_debug("%s, sk=%p, Smallest p used!\n",

					       dccp_role(sk), sk);

			}

		}



		dccp_timestamp(sk, &now);



		/*

		 * Calculate new round trip sample as per [RFC 3448, 4.3] by

		 * 	R_sample  =  (now - t_recvdata) - t_elapsed

		 */

		r_sample  = timeval_delta(&now, &packet->dccphtx_tstamp);

		if (unlikely(r_sample <= t_elapsed))

			DCCP_WARN("r_sample=%uus,t_elapsed=%uus\n",

		t_elapsed = dp->dccps_options_received.dccpor_elapsed_time * 10;



		if (unlikely(r_sample <= 0)) {

			DCCP_WARN("WARNING: R_sample (%ld) <= 0!\n", r_sample);

			r_sample = 0;

		} else if (unlikely(r_sample <= t_elapsed))

			DCCP_WARN("WARNING: r_sample=%ldus <= t_elapsed=%ldus\n",

				  r_sample, t_elapsed);

		else

			r_sample -= t_elapsed;
@@ -474,31 +495,25 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
			hctx->ccid3hctx_t_ld = now;



			ccid3_update_send_time(hctx);

			ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);

		} else {

			hctx->ccid3hctx_rtt = (hctx->ccid3hctx_rtt * 9) / 10 +

					      r_sample / 10;

			ccid3_hc_tx_update_x(sk, &now);

		}



		ccid3_pr_debug("%s, sk=%p, New RTT estimate=%uus, "

			       "r_sample=%us\n", dccp_role(sk), sk,

			       hctx->ccid3hctx_rtt, r_sample);

			ccid3_pr_debug("%s(%p), s=%u, w_init=%u, "

				       "R_sample=%ldus, X=%u\n", dccp_role(sk),

				       sk, hctx->ccid3hctx_s, w_init, r_sample,

				       hctx->ccid3hctx_x);



		/* Update receive rate */

		hctx->ccid3hctx_x_recv = x_recv;/* X_recv in bytes per sec */

			ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);

		} else {

			hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt +

					           (u32)r_sample        ) / 10;



		/* Update loss event rate */

		if (pinv == ~0 || pinv == 0)

			hctx->ccid3hctx_p = 0;

		else {

			hctx->ccid3hctx_p = 1000000 / pinv;

			ccid3_hc_tx_update_x(sk, &now);



			if (hctx->ccid3hctx_p < TFRC_SMALLEST_P) {

				hctx->ccid3hctx_p = TFRC_SMALLEST_P;

				ccid3_pr_debug("%s, sk=%p, Smallest p used!\n",

					       dccp_role(sk), sk);

			}

			ccid3_pr_debug("%s(%p), RTT=%uus (sample=%ldus), s=%u, "

				       "p=%u, X_calc=%u, X=%u\n", dccp_role(sk),

				       sk, hctx->ccid3hctx_rtt, r_sample,

				       hctx->ccid3hctx_s, hctx->ccid3hctx_p,

				       hctx->ccid3hctx_x_calc,

				       hctx->ccid3hctx_x);

		}



		/* unschedule no feedback timer */

CRA Git | Maintained and supported by SUSTech CRA and CCSE