From: Oleksandr Natalenko <oleksandr@natalenko.name>
To: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>,
Yousuk Seung <ysseung@google.com>,
Soheil Hassas Yeganeh <soheil@google.com>,
Adithya Abraham Philip <abrahamphilip@google.com>,
Eric Dumazet <edumazet@google.com>,
"David S. Miller" <davem@davemloft.net>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
David Ahern <dsahern@kernel.org>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Konstantin Demin <rockdrilla@gmail.com>
Subject: [RFC] tcp_bbr2: use correct 64-bit division
Date: Mon, 23 May 2022 00:29:37 +0200 [thread overview]
Message-ID: <4740526.31r3eYUQgx@natalenko.name> (raw)
Hello Neal.
It was reported to me [1] by Konstantin (in Cc) that BBRv2 code suffers from integer division issue on 32 bit systems.
Konstantin suggested a solution available in the same linked merge request and copy-pasted by me below for your convenience:
```
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 664c9e119787..fd3f89e3a8a6 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -312,7 +312,7 @@ static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now,
bytes = sk->sk_pacing_rate >> sk->sk_pacing_shift;
bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
- segs = max_t(u32, bytes / mss_now, bbr_min_tso_segs(sk));
+ segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk));
return segs;
}
diff --git a/net/ipv4/tcp_bbr2.c b/net/ipv4/tcp_bbr2.c
index fa49e17c47ca..488429f0f3d0 100644
--- a/net/ipv4/tcp_bbr2.c
+++ b/net/ipv4/tcp_bbr2.c
@@ -588,7 +588,7 @@ static void bbr_debug(struct sock *sk, u32 acked,
bbr_rate_kbps(sk, bbr_max_bw(sk)), /* bw: max bw */
0ULL, /* lb: [obsolete] */
0ULL, /* ib: [obsolete] */
- (u64)sk->sk_pacing_rate * 8 / 1000,
+ div_u64((u64)sk->sk_pacing_rate * 8, 1000),
acked,
tcp_packets_in_flight(tp),
rs->is_ack_delayed ? 'd' : '.',
@@ -698,7 +698,7 @@ static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now,
}
bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
- segs = max_t(u32, bytes / mss_now, bbr_min_tso_segs(sk));
+ segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk));
return segs;
}
```
Could you please evaluate this report and check whether it is correct, and also check whether the suggested patch is acceptable?
Thanks.
[1] https://gitlab.com/post-factum/pf-kernel/-/merge_requests/6
--
Oleksandr Natalenko (post-factum)
next reply other threads:[~2022-05-22 22:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-22 22:29 Oleksandr Natalenko [this message]
2022-05-24 8:01 ` [RFC] tcp_bbr2: use correct 64-bit division David Laight
2022-05-24 20:05 ` Neal Cardwell
2022-05-24 20:22 ` Eric Dumazet
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