To: nickpiggin@yahoo.com.au
CC: peterz@infradead.org, davem@davemloft.net, jarkao2@gmail.com,
       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,
       paulmck@linux.vnet.ibm.com
In-reply-to: <200807242038.36693.nickpiggin@yahoo.com.au> (message from Nick
	Piggin on Thu, 24 Jul 2008 20:38:35 +1000)
Subject: Re: Kernel WARNING: at net/core/dev.c:1330 __netif_schedule+0x2c/0x98()
References: <1216890648.7257.258.camel@twins> <20080724.023210.229338550.davem@davemloft.net> <1216894136.7257.266.camel@twins> <200807242038.36693.nickpiggin@yahoo.com.au>
Message-Id: <E1KLyUI-0006ZS-Cg@pomaz-ex.szeredi.hu>
From: Miklos Szeredi <miklos@szeredi.hu>
Date: Thu, 24 Jul 2008 12:55:58 +0200
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 725
Lines: 18

On Thu, 24 Jul 2008, Nick Piggin wrote:
> Hey, something kind of cool (and OT) I've just thought of that we can
> do with ticket locks is to take tickets for 2 (or 64K) nested locks,
> and then wait for them both (all), so the cost is N*lock + longest spin,
> rather than N*lock + N*avg spin.

Isn't this deadlocky?

E.g. one task takes ticket x=1, then other task comes in and takes x=2
and y=1, then first task takes y=2.  Then neither can actually
complete both locks.

Miklos
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