netdev - Re: [PATCH] b44: add 64 bit stats

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Message-ID: <1342759989.2626.5472.camel@edumazet-glaptop>
Date:	Fri, 20 Jul 2012 06:53:09 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kevin Groeneveld <kgroeneveld@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] b44: add 64 bit stats

On Thu, 2012-07-19 at 21:56 -0400, Kevin Groeneveld wrote:

> I am still trying to make sure I understand this fully.  I want to
> update some other drivers with 64 bit stats as well.  What you said
> seems to make sense, but...
> 
> I was looking at the virtio_net.c driver.  One spot in this driver
> which updates the stats is the receive_buf function.  recive_buf is
> called from virtnet_poll which is registered as a napi poll function.
> According to Documentation/networking/netdevices.txt the poll function
> is called in a softirq context.  However, the function which reads the
> stats uses u64_stats_fetch_begin/u64_stats_fetch_retry.  Shouldn't
> this be u64_stats_fetch_begin_bh/u64_stats_fetch_retry_bh for the
> exact reasons you described for my b44 patch?

Absolutely. You can argue that probably nobody use this driver on a
32bit UP machine, but technically speaking the current implementation is
racy.


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