linux-kernel - Re: Kernel WARNING: at net/core/dev.c:1330 __netif

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Message-ID: <20080727203757.GA2527@ami.dom.local>
Date:	Sun, 27 Jul 2008 22:37:57 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	johannes@...solutions.net, netdev@...eo.de, peterz@...radead.org,
	Larry.Finger@...inger.net, kaber@...sh.net,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org, mingo@...hat.com
Subject: Re: Kernel WARNING: at net/core/dev.c:1330
	__netif_schedule+0x2c/0x98()

On Sat, Jul 26, 2008 at 05:34:34PM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Sat, 26 Jul 2008 15:18:38 +0200
> 
> > I guess some additional synchronization will be added yet to prevent
> > parallel freeze and especially unfreeze.
> 
> Yes, that could be a problem.  Using test_and_set_bit() can
> guard the freezing sequence itself, but it won't handle
> letting two threads of control freeze and unfreeze safely
> without a reference count.
> 
> We want this thing to be able to be used flexbly, which means
> we can't just assume that this is a short code sequence and
> the unfreeze will come quickly.  That pretty much rules
> out using a new lock around the operation or anything
> like that.
> 
> So I guess we could replace the state bit with a reference
> count.  It doesn't even need to be atomic since it is set
> and tested under dev_queue->_xmit_lock
 
Looks like enough to me. (Probably it could even share space with
the state.)

Jarek P.
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