linux-kernel - Re: [PATCH resend] drop_monitor: fix trace_napi_poll

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Date:	Mon, 31 Aug 2009 08:31:51 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	David Miller <davem@...emloft.net>,
	Neil Horman <nhorman@...driver.com>,
	Wei Yongjun <yjwei@...fujitsu.com>,
	Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH resend] drop_monitor: fix trace_napi_poll_hit()

Xiao Guangrong a écrit :
> The net_dev of backlog napi is NULL, like below:
> 
> __get_cpu_var(softnet_data).backlog.dev == NULL
> 
> So, we should check it in napi tracepoint's probe function
> 
> Acked-by: Neil Horman <nhorman@...driver.com>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  net/core/drop_monitor.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
> index 9d66fa9..d311202 100644
> --- a/net/core/drop_monitor.c
> +++ b/net/core/drop_monitor.c
> @@ -182,7 +182,8 @@ static void trace_napi_poll_hit(struct napi_struct *napi)
>  	/*
>  	 * Ratelimit our check time to dm_hw_check_delta jiffies
>  	 */
> -	if (!time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta))
> +	if (!napi->dev ||
> +	    !time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta))
>  		return;
>  
>  	rcu_read_lock();


This reminds me dev->last_rx is not anymore updated, unless special conditions
are met.

Test done in trace_napi_poll_hit() is probably not good, even with a non null napi->dev
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