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

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Date:	Thu, 24 Jul 2008 12:55:58 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	nickpiggin@...oo.com.au
CC:	peterz@...radead.org, davem@...emloft.net, jarkao2@...il.com,
	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,
	paulmck@...ux.vnet.ibm.com
Subject: Re: Kernel WARNING: at net/core/dev.c:1330 __netif_schedule+0x2c/0x98()

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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