netdev - Re: [net 1/1] tipc: initialize broadcast link stale counter correctly

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Date:   Fri, 12 Oct 2018 08:41:24 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     Jon Maloy <jon.maloy@...csson.com>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>
CC:     <gordan.mihaljevic@...tech.com.au>, <tung.q.nguyen@...tech.com.au>,
        <hoang.h.le@...tech.com.au>, <canh.d.luu@...tech.com.au>,
        <tipc-discussion@...ts.sourceforge.net>
Subject: Re: [net 1/1] tipc: initialize broadcast link stale counter correctly

On 10/12/2018 04:02 AM, Jon Maloy wrote:
> In the commit referred to below we added link tolerance as an additional
> criteria for declaring broadcast transmission "stale" and resetting the
> unicast links to the affected node.
> 
> Unfortunately, this 'improvement' introduced two bugs, which each and
> one alone cause only limited problems, but combined lead to seemingly
> stochastic unicast link resets, depending on the amount of broadcast
> traffic transmitted.
> 
> The first issue, a missing initialization of the 'tolerance' field of
> the receiver broadcast link, was recently fixed by commit 047491ea334a
> ("tipc: set link tolerance correctly in broadcast link").
> 
> Ths second issue, where we omit to reset the 'stale_cnt' field of
> the same link after a 'stale' period is over, leads to this counter
> accumulating over time, and in the absence of the 'tolerance' criteria
> leads to the above described symptoms. This commit adds the missing
> initialization.
> 
> Fixes: a4dc70d46cf1 ("tipc: extend link reset criteria for stale packet
> retransmission")
> 
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Acked-by: Ying Xue <ying.xue@...driver.com>

> ---
>  net/tipc/link.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/tipc/link.c b/net/tipc/link.c
> index f6552e4..201c3b5 100644
> --- a/net/tipc/link.c
> +++ b/net/tipc/link.c
> @@ -1041,6 +1041,7 @@ static int tipc_link_retrans(struct tipc_link *l, struct tipc_link *r,
>  	if (r->last_retransm != buf_seqno(skb)) {
>  		r->last_retransm = buf_seqno(skb);
>  		r->stale_limit = jiffies + msecs_to_jiffies(r->tolerance);
> +		r->stale_cnt = 0;
>  	} else if (++r->stale_cnt > 99 && time_after(jiffies, r->stale_limit)) {
>  		link_retransmit_failure(l, skb);
>  		if (link_is_bc_sndlink(l))
>