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

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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: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gerrit Renker 2007-03-20 14:56:11 -03:00 committed by David S. Miller
parent 8699be7d24
commit 1266adee12
1 changed files with 12 additions and 23 deletions
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35
net/dccp/ccids/ccid3.c
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@ -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),