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

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Message-ID: <alpine.LFD.2.00.0907091401040.24704@localhost.localdomain>
Date:	Thu, 9 Jul 2009 14:03:50 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jarek Poplawski <jarkao2@...il.com>
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, 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.

Thanks,

	tglx
---

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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