Commit 1266adee authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[CCID3]: Remove race condition and update t_ipi when `s' changes 



This:

 1. removes a race condition in the access to the scheduled send time t_nom which
    results from allowing asynchronous r/w access to t_nom without locks;

 2. updates the inter-packet interval t_ipi = s/X when `s' changes, following a
    suggestion by Ian McDonald.

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@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8699be7d

net/dccp/ccids/ccid3.c

+12 −23
Original line number Diff line number Diff line
@@ -82,20 +82,14 @@ static void ccid3_hc_tx_set_state(struct sock *sk, 
}



/*

 * Recalculate scheduled nominal send time t_nom, inter-packet interval

 * t_ipi, and delta value. Should be called after each change to X.

 * Recalculate t_ipi and delta (should be called whenever X changes)

 */

static inline void ccid3_update_send_time(struct ccid3_hc_tx_sock *hctx)

static inline void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hctx)

{

	timeval_sub_usecs(&hctx->ccid3hctx_t_nom, hctx->ccid3hctx_t_ipi);



	/* Calculate new t_ipi = s / X_inst (X_inst is in 64 * bytes/second) */

	hctx->ccid3hctx_t_ipi = scaled_div(hctx->ccid3hctx_s,

					   hctx->ccid3hctx_x >> 6);



	/* Update nominal send time with regard to the new t_ipi */

	timeval_add_usecs(&hctx->ccid3hctx_t_nom, hctx->ccid3hctx_t_ipi);



	/* Calculate new delta by delta = min(t_ipi / 2, t_gran / 2) */

	hctx->ccid3hctx_delta = min_t(u32, hctx->ccid3hctx_t_ipi / 2,

					   TFRC_OPSYS_HALF_TIME_GRAN);
@@ -119,8 +113,6 @@ static inline void ccid3_update_send_time(struct ccid3_hc_tx_sock *hctx) 
 *       fine-grained resolution of sending rates. This requires scaling by 2^6

 *       throughout the code. Only X_calc is unscaled (in bytes/second).

 *

 * 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)
@@ -151,7 +143,7 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now) 
			       "X_recv=%llu\n", old_x >> 6, hctx->ccid3hctx_x >> 6,

			       hctx->ccid3hctx_x_calc, hctx->ccid3hctx_x_recv >> 6);



		ccid3_update_send_time(hctx);

		ccid3_update_send_interval(hctx);

	}

}
@@ -161,14 +153,12 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now) 
 */

static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len)

{

	hctx->ccid3hctx_s = hctx->ccid3hctx_s == 0 ? len :

			    (9 * hctx->ccid3hctx_s + len) / 10;

	/*

	 * Note: We could do a potential optimisation here - when `s' changes,

	 *	 recalculate sending rate and consequently t_ipi, t_delta, and

	 *	 t_now. This is however non-standard, and the benefits are not

	 *	 clear, so it is currently left out.

	 */

	const u16 old_s = hctx->ccid3hctx_s;



	hctx->ccid3hctx_s = old_s == 0 ? len : (9 * old_s + len) / 10;



	if (hctx->ccid3hctx_s != old_s)

		ccid3_update_send_interval(hctx);

}



/*
@@ -228,7 +218,7 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) 
		/* The value of R is still undefined and so we can not recompute

		 * the timout value. Keep initial value as per [RFC 4342, 5]. */

		t_nfb = TFRC_INITIAL_TIMEOUT;

		ccid3_update_send_time(hctx);

		ccid3_update_send_interval(hctx);

		break;

	case TFRC_SSTATE_FBACK:

		/*
@@ -334,8 +324,7 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb) 
		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);



		/* Set initial sending rate X/s to 1pps (X is scaled by 2^6) */

		ccid3_hc_tx_update_s(hctx, skb->len);

		hctx->ccid3hctx_x = hctx->ccid3hctx_s;

		hctx->ccid3hctx_x = hctx->ccid3hctx_s = skb->len;

		hctx->ccid3hctx_x <<= 6;



		/* First timeout, according to [RFC 3448, 4.2], is 1 second */
@@ -484,7 +473,7 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
			hctx->ccid3hctx_x    = scaled_div(w_init << 6, r_sample);

			hctx->ccid3hctx_t_ld = now;



			ccid3_update_send_time(hctx);

			ccid3_update_send_interval(hctx);



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

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

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