netdev - Re: rndis gadget: Inconsistent locking

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Message-ID: <20110112134136.GB9920@ff.dom.local>
Date:	Wed, 12 Jan 2011 13:41:36 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...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

On Wed, Jan 12, 2011 at 02:32:20PM +0100, Eric Dumazet wrote:
> Le mercredi 12 janvier 2011 ?? 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.

Well, I'm OK with anything, but this thread gets older and older ;-)

Jarek P.
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