netdev - Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl

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Message-ID: <20080814083127.GA12217@ff.dom.local>
Date:	Thu, 14 Aug 2008 08:31:27 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl_lock().

On Thu, Aug 14, 2008 at 06:16:32PM +1000, Herbert Xu wrote:
> On Thu, Aug 14, 2008 at 07:59:07AM +0000, Jarek Poplawski wrote:
> > 
> > net: Change handling of the __QDISC_STATE_SCHED flag in net_tx_action().
> > 
> > Change handling of the __QDISC_STATE_SCHED flag in net_tx_action() to
> > enable proper control in dev_deactivate_queue(). Now, if this flag is
> > seen as unset under root_lock means a qdisc can't be netif_scheduled.
> > 
> > 
> > Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
> 
> Well this probably works in practice but at least on paper it
> is vulnerable to live-lock if the net_tx_action side always gets
> to the trylock stage and loses to the waiting side.
> 
> An aliveness flag would be the safest.

I'm not sure of your point... This patch is only to fix my yesterday's
doubt #1, and it doesn't introduce, I hope, any new live-lock
vulnerabity. So, if you mean doubt #2, there is needed a separate
patch, but I'm not sure there is a need to add a flag. I've thougt
about a counter in a Qdisc for consecutive requeues with
netif_schedule, so we could break after some limit. Of course, your
idea could be simpler and better, but if I could only see some code...

Cheers,
Jarek P.
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