Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[David Miller]

From: Konstantin Khlebnikov 
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 

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.

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[David Miller]

From: Konstantin Khlebnikov 
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 

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.

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Eric Dumazet]

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 
> ---
>  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) * 800;
> - 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) * 8;
do_div(rate64, avg_rtt ?: 1);
rate = (u32)rate64;

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Eric Dumazet]

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 
> ---
>  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) * 800;
> - 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) * 8;
do_div(rate64, avg_rtt ?: 1);
rate = (u32)rate64;

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Stephen Hemminger]

On Wed, 1 Nov 2017 13:47:17 +
Lawrence Brakmo  wrote:

> Thank you for finding and fixing this.
> 
> On 11/1/17, 6:32 AM, "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 khlebni...@yandex-team.ru
> Acked-by: Lawrence Brakmo 
> ---
>  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) * 800;
> - 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?

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Stephen Hemminger]

On Wed, 1 Nov 2017 13:47:17 +
Lawrence Brakmo  wrote:

> Thank you for finding and fixing this.
> 
> On 11/1/17, 6:32 AM, "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 khlebni...@yandex-team.ru
> Acked-by: Lawrence Brakmo 
> ---
>  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) * 800;
> - 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?

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Lawrence Brakmo]

Thank you for finding and fixing this.

On 11/1/17, 6:32 AM, "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 khlebni...@yandex-team.ru
Acked-by: Lawrence Brakmo 
---
 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) * 800;
-   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

Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Lawrence Brakmo]

Thank you for finding and fixing this.

On 11/1/17, 6:32 AM, "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 khlebni...@yandex-team.ru
Acked-by: Lawrence Brakmo 
---
 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) * 800;
-   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

[PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Konstantin Khlebnikov]

Average RTT could become zero. This happened in real life at least twice.
This patch treats zero as 1us.

Signed-off-by: Konstantin Khlebnikov 
---
 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) * 800;
-   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

[PATCH] tcp_nv: fix division by zero in tcpnv_acked()

[Konstantin Khlebnikov]

Average RTT could become zero. This happened in real life at least twice.
This patch treats zero as 1us.

Signed-off-by: Konstantin Khlebnikov 
---
 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) * 800;
-   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