netdev - Re: [Bugme-new] [Bug 10326] New: inconsistent lock state in net_rx

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Message-ID: <20080327085542.GA2778@ami.dom.local>
Date:	Thu, 27 Mar 2008 09:55:42 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org,
	marcus@...ter.se,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Bugme-new] [Bug 10326] New: inconsistent lock state in
	net_rx_action

On Wed, Mar 26, 2008 at 05:14:03PM -0700, Andrew Morton wrote:
...
> > >> http://bugzilla.kernel.org/show_bug.cgi?id=10326
...
> No, it's not an irq_disable() thing, directly.
> 
> What lockdep is saying is that sky2_poll() is taking napi->poll_lock for
> writing with softirqs enabled, but net_rx_action() takes the same lock from
> within softirq context.
> 
> If sky2_poll() always takes napi->poll_lock under local_irq_disable() then
> that would be a lockdep bug.

sky2_poll() doesn't take napi->poll_lock; this lock is taken by
netpoll_poll() before calling sky2_poll(). And before this hardirqs
are disabled in write_msg(). So, theoretically lockdep could be right
if sky2_poll() would enable irqs after this. (If it were done in
netpoll - lockdep should warn before or after sky2_poll() call.)
But I really can't see any such possibility in sky2_poll().

Regards,
Jarek P.
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