From: Eric Dumazet
dctcp_alpha can be read by from dctcp_get_info() without
synchro, so use WRITE_ONCE() to prevent compiler from using
dctcp_alpha as a temporary variable.
Also, playing with small dctcp_shift_g (like 1), can expose
an overflow with 32bit values shifted 9 times before divide.
Use an u64 field to avoid this problem, and perform the divide
only if acked_bytes_ecn is not zero.
Signed-off-by: Eric Dumazet
---
net/ipv4/tcp_dctcp.c | 26 --
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index
4c41c1287197eb4748198ae9532d1f6233aa7f6a..7092a61c4dc8465fcf17ff71b289cf25bbb8b559
100644
--- a/net/ipv4/tcp_dctcp.c
+++ b/net/ipv4/tcp_dctcp.c
@@ -204,20 +204,26 @@ static void dctcp_update_alpha(struct sock *sk, u32 flags)
/* Expired RTT */
if (!before(tp->snd_una, ca->next_seq)) {
- /* For avoiding denominator == 1. */
- if (ca->acked_bytes_total == 0)
- ca->acked_bytes_total = 1;
+ u64 bytes_ecn = ca->acked_bytes_ecn;
+ u32 alpha = ca->dctcp_alpha;
/* alpha = (1 - g) * alpha + g * F */
- ca->dctcp_alpha = ca->dctcp_alpha -
- (ca->dctcp_alpha >> dctcp_shift_g) +
- (ca->acked_bytes_ecn << (10U -
dctcp_shift_g)) /
- ca->acked_bytes_total;
- if (ca->dctcp_alpha > DCTCP_MAX_ALPHA)
- /* Clamp dctcp_alpha to max. */
- ca->dctcp_alpha = DCTCP_MAX_ALPHA;
+ alpha -= alpha >> dctcp_shift_g;
+ if (bytes_ecn) {
+ /* If dctcp_shift_g == 1, a 32bit value would overflow
+* after 8 Mbytes.
+*/
+ bytes_ecn <<= (10 - dctcp_shift_g);
+ do_div(bytes_ecn, max(1U, ca->acked_bytes_total));
+ alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);
+ }
+ /* dctcp_alpha can be read from dctcp_get_info() without
+* synchro, so we ask compiler to not use dctcp_alpha
+* as a temporary variable in prior operations.
+*/
+ WRITE_ONCE(ca->dctcp_alpha, alpha);
dctcp_reset(tp, ca);
}
}
--
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