netdev - Re: [net-next PATCH] igb: update adapter stats when reading /proc/net/dev.

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Date:	Tue, 5 Oct 2010 23:16:37 +0200 (CEST)
From:	Jesper Dangaard Brouer <hawk@...u.dk>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	Jesper Dangaard Brouer <hawk@...x.dk>,
	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [net-next PATCH] igb: update adapter stats when reading
 /proc/net/dev.

On Tue, 5 Oct 2010, Eric Dumazet wrote:

> Le mardi 05 octobre 2010 à 17:19 +0200, Eric Dumazet a écrit :
>> Le mardi 05 octobre 2010 à 16:53 +0200, Jesper Dangaard Brouer a écrit :
>>
>>> Its already racy, because "ethtool -S" reads out the stats immediately,
>>> and thus races with the timer.
>>>
>>> See: igb_ethtool.c
>>>  igb_get_ethtool_stats() invoke igb_update_stats(adapter);
>>>
>>
>> You would be surprised how many bugs are waiting to be found and
>> fixed ;)
>
> I took a look at igb stats, and it appears they also are racy on 32bit
> arches. igb uses u64 counters, with no synchronization between
> producers(writers) and consumers(readers).

Are you saying, that we need more than a simple mutex in 
igb_update_stats()?


> Some fixes are needed ;)

The question is then if Intel wants to fix it, or let it be up to you or 
me?

Cheers,
   Jesper Brouer

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