| Message ID | 150954313588.153848.10192893966808917578.stgit@buzz |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | tcp_nv: fix division by zero in tcpnv_acked() | expand |
Thank you for finding and fixing this.
On 11/1/17, 6:32 AM, "Konstantin Khlebnikov" <khlebnikov@yandex-team.ru> wrote:
Average RTT could become zero. This happened in real life at least twice.
This patch treats zero as 1us.
Signed-off-by: Konstantin Khlebnikov khlebnikov@yandex-team.ru
Acked-by: Lawrence Brakmo <Brakmo@fb.com>
---
net/ipv4/tcp_nv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c
index 1ff73982e28c..125fc1450b01 100644
--- a/net/ipv4/tcp_nv.c
+++ b/net/ipv4/tcp_nv.c
@@ -252,7 +252,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample)
/* rate in 100's bits per second */
rate64 = ((u64)sample->in_flight) * 8000000;
- rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100));
+ rate = (u32)div64_u64(rate64, (u64)(avg_rtt ?: 1) * 100);
/* Remember the maximum rate seen during this RTT
* Note: It may be more than one RTT. This function should be
On Wed, 1 Nov 2017 13:47:17 +0000 Lawrence Brakmo <brakmo@fb.com> wrote: > Thank you for finding and fixing this. > > On 11/1/17, 6:32 AM, "Konstantin Khlebnikov" <khlebnikov@yandex-team.ru> wrote: > > Average RTT could become zero. This happened in real life at least twice. > This patch treats zero as 1us. > > Signed-off-by: Konstantin Khlebnikov khlebnikov@yandex-team.ru > Acked-by: Lawrence Brakmo <Brakmo@fb.com> > --- > net/ipv4/tcp_nv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c > index 1ff73982e28c..125fc1450b01 100644 > --- a/net/ipv4/tcp_nv.c > +++ b/net/ipv4/tcp_nv.c > @@ -252,7 +252,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample) > > /* rate in 100's bits per second */ > rate64 = ((u64)sample->in_flight) * 8000000; > - rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100)); > + rate = (u32)div64_u64(rate64, (u64)(avg_rtt ?: 1) * 100); Why is this code using expensive 64 bit by 64 bit divide when avg_rtt should never be bigger than 32 bits?
On Wed, 2017-11-01 at 16:32 +0300, Konstantin Khlebnikov wrote: > Average RTT could become zero. This happened in real life at least twice. > This patch treats zero as 1us. > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> > --- > net/ipv4/tcp_nv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c > index 1ff73982e28c..125fc1450b01 100644 > --- a/net/ipv4/tcp_nv.c > +++ b/net/ipv4/tcp_nv.c > @@ -252,7 +252,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample) > > /* rate in 100's bits per second */ > rate64 = ((u64)sample->in_flight) * 8000000; > - rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100)); > + rate = (u32)div64_u64(rate64, (u64)(avg_rtt ?: 1) * 100); > > /* Remember the maximum rate seen during this RTT > * Note: It may be more than one RTT. This function should be > BTW, this div64_u64() could be replaced by a u32 divide (aka do_div()), slightly less expensive. rate64 = ((u64)sample->in_flight) * 80000; do_div(rate64, avg_rtt ?: 1); rate = (u32)rate64;
From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Date: Wed, 01 Nov 2017 16:32:15 +0300 > Average RTT could become zero. This happened in real life at least twice. > This patch treats zero as 1us. > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Applied and queued up for -stable, thank you. Indeed, as others have mentioned, a cheaper divide should be used but that is a separate issue from this fix and therefore should be done in a separate patch. Thanks again.
diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c index 1ff73982e28c..125fc1450b01 100644 --- a/net/ipv4/tcp_nv.c +++ b/net/ipv4/tcp_nv.c @@ -252,7 +252,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample) /* rate in 100's bits per second */ rate64 = ((u64)sample->in_flight) * 8000000; - rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100)); + rate = (u32)div64_u64(rate64, (u64)(avg_rtt ?: 1) * 100); /* Remember the maximum rate seen during this RTT * Note: It may be more than one RTT. This function should be
Average RTT could become zero. This happened in real life at least twice. This patch treats zero as 1us. Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> --- net/ipv4/tcp_nv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)