Date: Sat, 26 Jul 2008 17:34:34 -0700 (PDT)
Message-Id: <20080726.173434.48036095.davem@davemloft.net>
To: jarkao2@gmail.com
Cc: johannes@sipsolutions.net, netdev@axxeo.de, peterz@infradead.org,
       Larry.Finger@lwfinger.net, kaber@trash.net,
       torvalds@linux-foundation.org, akpm@linux-foundation.org,
       netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
       linux-wireless@vger.kernel.org, mingo@redhat.com
Subject: Re: Kernel WARNING: at net/core/dev.c:1330
 __netif_schedule+0x2c/0x98()
From: David Miller <davem@davemloft.net>
In-Reply-To: <20080726131838.GA2873@ami.dom.local>
References: <20080725200137.GC3107@ami.dom.local>
	<20080726.021846.236624483.davem@davemloft.net>
	<20080726131838.GA2873@ami.dom.local>
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From: Jarek Poplawski <jarkao2@gmail.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

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