linux-kernel - Re: Soft-Lockup/Race in networking in 2.6.31-rc1+195 ( possibly?caused by netem)

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Message-ID: <20090709132256.GB3651@ami.dom.local>
Date:	Thu, 9 Jul 2009 15:22:56 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andres Freund <andres@...razel.de>,
	Joao Correia <joaomiguelcorreia@...il.com>,
	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: Soft-Lockup/Race in networking in 2.6.31-rc1+195 (
	possibly?caused by netem)

On Thu, Jul 09, 2009 at 02:03:50PM +0200, Thomas Gleixner wrote:
> On Thu, 9 Jul 2009, Jarek Poplawski wrote:
> > > 
> > > I have the feeling that the code relies on some implicit cpu
> > > boundness, which is not longer guaranteed with the timer migration
> > > changes, but that's a question for the network experts.
> > 
> > As a matter of fact, I've just looked at this __netif_schedule(),
> > which really is cpu bound, so you might be 100% right.
> 
> So the watchdog is the one which causes the trouble. The patch below
> should fix this.

I hope so. On the other hand it seems it should work with this
migration yet, so it probably needs additional debugging.

Thanks,
Jarek P.

> ---
> 
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index 24d17ce..fbe554f 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -485,7 +485,7 @@ void qdisc_watchdog_schedule(struct qdisc_watchdog *wd, psched_time_t expires)
>  	wd->qdisc->flags |= TCQ_F_THROTTLED;
>  	time = ktime_set(0, 0);
>  	time = ktime_add_ns(time, PSCHED_TICKS2NS(expires));
> -	hrtimer_start(&wd->timer, time, HRTIMER_MODE_ABS);
> +	hrtimer_start(&wd->timer, time, HRTIMER_MODE_ABS_PINNED);
>  }
>  EXPORT_SYMBOL(qdisc_watchdog_schedule);
>  
--
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