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authorEric Dumazet <edumazet@google.com>2015-06-10 22:11:17 -0700
committerDavid S. Miller <davem@davemloft.net>2015-06-10 23:28:33 -0700
commitf9c2ff22bb2df7b8f153afd2a4bea07176bad144 (patch)
tree3afd7e841d7d0b785d7e1e8678e5cd2372ca2d14 /net
parent1edaa7e8a7e753bd42d795bf289a6488aeae7f56 (diff)
net: tcp: dctcp_update_alpha() fixes.
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 <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_dctcp.c26
1 files changed, 16 insertions, 10 deletions
diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index 4c41c1287197..7092a61c4dc8 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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