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| author | Eric Dumazet <edumazet@google.com> | 2015-06-11 08:11:17 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-06-11 09:28:33 +0300 |
| commit | f9c2ff22bb2df7b8f153afd2a4bea07176bad144 (patch) | |
| tree | 3afd7e841d7d0b785d7e1e8678e5cd2372ca2d14 /net/ipv4 | |
| parent | 1edaa7e8a7e753bd42d795bf289a6488aeae7f56 (diff) | |
| download | linux-f9c2ff22bb2df7b8f153afd2a4bea07176bad144.tar.xz | |
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/ipv4')
| -rw-r--r-- | net/ipv4/tcp_dctcp.c | 26 |
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); } } |