Subject: Re: [PATCH 4/4 v3] net: Fix for dst_negative_advice

From: Stephen Hemminger <[email-masked]>
Date: Mon, 19 Oct 2009 13:12:09 +0900

On Sun, 18 Oct 2009 18:38:16 +0530
Krishna Kumar <[email-masked]> wrote:

> From: Krishna Kumar <[email-masked]>
> 
> dst_negative_advice() should check for changed dst and reset
> sk_tx_queue_mapping accordingly. Pass sock to the callers of
> dst_negative_advice.
> 
> (sk_reset_txq is defined just for use by dst_negative_advice. The
> only way I could find to get around this is to move dst_negative_()
> from dst.h to dst.c, include sock.h in dst.c, etc)
> 
> Signed-off-by: Krishna Kumar <[email-masked]>
> ---
>  include/net/dst.h      |   12 ++++++++++--
>  net/core/sock.c        |    6 ++++++
>  net/dccp/timer.c       |    4 ++--
>  net/decnet/af_decnet.c |    2 +-
>  net/ipv4/tcp_timer.c   |    4 ++--
>  5 files changed, 21 insertions(+), 7 deletions(-)
> 
> diff -ruNp org/include/net/dst.h new/include/net/dst.h
> --- org/include/net/dst.h	2009-10-16 21:30:56.000000000 +0530
> +++ new/include/net/dst.h	2009-10-16 21:31:30.000000000 +0530
> @@ -222,11 +222,19 @@ static inline void dst_confirm(struct ds
>  		neigh_confirm(dst->neighbour);
>  }
>  
> -static inline void dst_negative_advice(struct dst_entry **dst_p)
> +static inline void dst_negative_advice(struct dst_entry **dst_p,
> +				       struct sock *sk)
>  {
>  	struct dst_entry * dst = *dst_p;
> -	if (dst && dst->ops->negative_advice)
> +	if (dst && dst->ops->negative_advice) {
>  		*dst_p = dst->ops->negative_advice(dst);
> +
> +		if (dst != *dst_p) {
> +			extern void sk_reset_txq(struct sock *sk);
> +
> +			sk_reset_txq(sk);
> +		}
> +	}
>  }
>  
>  static inline void dst_link_failure(struct sk_buff *skb)
> diff -ruNp org/net/core/sock.c new/net/core/sock.c
> --- org/net/core/sock.c	2009-10-16 21:30:56.000000000 +0530
> +++ new/net/core/sock.c	2009-10-16 21:32:33.000000000 +0530
> @@ -352,6 +352,12 @@ discard_and_relse:
>  }
>  EXPORT_SYMBOL(sk_receive_skb);
>  
> +void sk_reset_txq(struct sock *sk)
> +{
> +	sk_tx_queue_clear(sk);
> +}
> +EXPORT_SYMBOL(sk_reset_txq);
> +
>  struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie)
>  {
>  	struct dst_entry *dst = sk->sk_dst_cache;
> diff -ruNp org/net/dccp/timer.c new/net/dccp/timer.c
> --- org/net/dccp/timer.c	2009-10-16 21:30:56.000000000 +0530
> +++ new/net/dccp/timer.c	2009-10-16 21:31:30.000000000 +0530
> @@ -38,7 +38,7 @@ static int dccp_write_timeout(struct soc
>  
>  	if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
>  		if (icsk->icsk_retransmits != 0)
> -			dst_negative_advice(&sk->sk_dst_cache);
> +			dst_negative_advice(&sk->sk_dst_cache, sk);
>  		retry_until = icsk->icsk_syn_retries ?
>  			    : sysctl_dccp_request_retries;
>  	} else {
> @@ -63,7 +63,7 @@ static int dccp_write_timeout(struct soc
>  			   Golden words :-).
>  		   */
>  
> -			dst_negative_advice(&sk->sk_dst_cache);
> +			dst_negative_advice(&sk->sk_dst_cache, sk);
>  		}
>  
>  		retry_until = sysctl_dccp_retries2;
> diff -ruNp org/net/decnet/af_decnet.c new/net/decnet/af_decnet.c
> --- org/net/decnet/af_decnet.c	2009-10-16 21:30:56.000000000 +0530
> +++ new/net/decnet/af_decnet.c	2009-10-16 21:31:30.000000000 +0530
> @@ -1955,7 +1955,7 @@ static int dn_sendmsg(struct kiocb *iocb
>  	}
>  
>  	if ((flags & MSG_TRYHARD) && sk->sk_dst_cache)
> -		dst_negative_advice(&sk->sk_dst_cache);
> +		dst_negative_advice(&sk->sk_dst_cache, sk);
>  
>  	mss = scp->segsize_rem;
>  	fctype = scp->services_rem & NSP_FC_MASK;
> diff -ruNp org/net/ipv4/tcp_timer.c new/net/ipv4/tcp_timer.c
> --- org/net/ipv4/tcp_timer.c	2009-10-16 21:30:56.000000000 +0530
> +++ new/net/ipv4/tcp_timer.c	2009-10-16 21:31:30.000000000 +0530
> @@ -141,14 +141,14 @@ static int tcp_write_timeout(struct sock
>  
>  	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
>  		if (icsk->icsk_retransmits)
> -			dst_negative_advice(&sk->sk_dst_cache);
> +			dst_negative_advice(&sk->sk_dst_cache, sk);
>  		retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
>  	} else {
>  		if (retransmits_timed_out(sk, sysctl_tcp_retries1)) {
>  			/* Black hole detection */
>  			tcp_mtu_probing(icsk, sk);
>  
> -			dst_negative_advice(&sk->sk_dst_cache);
> +			dst_negative_advice(&sk->sk_dst_cache, sk);
>  		}
>  
>  		retry_until = sysctl_tcp_retries2;

It is good that your patch is broken in pieces, but will the intermediate patches
still function correctly. I.e are they bisect safe?