netdev - Re: rndis gadget: Inconsistent locking

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Date:	Wed, 12 Jan 2011 14:32:20 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	David Brownell <david-b@...bell.net>,
	Michał Nazarewicz <m.nazarewicz@...sung.com>,
	Neil Jones <neiljay@...il.com>, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: rndis gadget: Inconsistent locking

Le mercredi 12 janvier 2011 à 13:23 +0000, Jarek Poplawski a écrit :
> On Wed, Jan 12, 2011 at 02:07:12PM +0100, Eric Dumazet wrote:
> ...
> > 
> > Hmm... 
> > 
> > So all net devices in gen_ndis_query_resp() should have a
> > ndo_get_stats() or ndo_get_stats64() method, not allowed to use
> > spin_lock_bh() / spin_unlock_bh()
> > 
> > If yes, we should add big fat comments to pn_net_stats()/eth_get_stats() so that nobody
> > tries to revert your patch ;)
> 
> I'm not sure I got your point: my patch could be replaced with
> ndo_get_stats64() implementing irq safe locking or by changing
> gen_ndis_query_resp() calling context. It's intended as a fast
> (compatible) fix.

I was mentioning that we tried in past months to remove useless
ndo_get_stats() methods that were only doing :

return &net->stats;

random commit : b27d50a9ff5cf2775b7a4daf5

Another possibility would be to use u64_stats_sync.h for these txq
counters.

(no locking needed to read counters, only a seqcount fetch/retry)

As a bonus, no overhead on 64bit arches.


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