netdev - Re: deadlocks if use htb

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Date:	Thu, 18 Dec 2008 08:17:37 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Badalian Vyacheslav <slavon@...telecom.ru>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: deadlocks if use htb

On Thu, Dec 18, 2008 at 09:43:51AM +0300, Badalian Vyacheslav wrote:
> Hello
> result: Patch 2+3 = uptime 7 days without crashes.
> May i revert patches and try single new patch?

Here is my current opinion on this bug:

1) I'm almost sure it's not a htb, but hrtimers bug (some race),

2) the htb patches you've tested are not "the proper" way of fixing
   it; I see substantial changes in hrtimers code in the "-tip" tree
   (probably for 2.6.29), which, probably, you'll be advised by
   hrtimers maintainers to try, and I guess, it's not easy on a
   production system,

So, it's up to you:

1) since these patches work for you, you can stop with testing and
   wait with these patched kernels until 2.6.29 (I can propose this
   #2 patch as a temporary fix then),

2) for curiosity you could try this patch #4 alone on one box first
   (after reverting at least patch #2), but again: if it works, it
   could be only treated as a temporary hack, and alternative of #2.

Thanks,
Jarek P.

> 
> > On Thu, Dec 11, 2008 at 08:46:06AM +0000, Jarek Poplawski wrote:
> >   
> >> On Wed, Dec 10, 2008 at 06:14:28PM +0300, Badalian Vyacheslav wrote:
> >>     
> >>> Hello again! Sorry for long away.
> >>>       
> >> Hi!
> >>
> >>     
> >>> I was go away from this work for long time.
> >>>
> >>> May we return to this bug?
> >>> Servers at last stable kernel 2.6.27.8
> >>> HZ=1000, HR=off, DynamicTicks=off, hysteresis=1
> >>> Sorry - no patched, update do not i. Do you have fresh patches or ideas
> >>> for tests?
> >>>       
> >> Not much, but I can have if you only are willing to test them...
> >> I attach below a patch which combines 2 patches I sent yesterday to
> >> netdev (PATCH 7/6 and 8/6) vs. 2.6.27.7 (named testing patch #3 here).
> >>
> >> You can still try the testing patch #2 I sent previously (quoted below)
> >> with or without this new #3 patch.
> >>
> >>     
> >
> > Here is another idea worth checking (instead of patch #2).
> >
> > Jarek P.
> >
> > --- (testing patch #4)
> >
> > diff -Nurp a2.6.27.7/net/sched/sch_htb.c b2.6.27.7/net/sched/sch_htb.c
> > --- a2.6.27.7/net/sched/sch_htb.c	2008-12-11 08:16:16.000000000 +0000
> > +++ b2.6.27.7/net/sched/sch_htb.c	2008-12-15 10:44:32.000000000 +0000
> > @@ -924,6 +924,7 @@ static struct sk_buff *htb_dequeue(struc
> >  		}
> >  	}
> >  	sch->qstats.overlimits++;
> > +	qdisc_watchdog_cancel(&q->watchdog);
> >  	qdisc_watchdog_schedule(&q->watchdog, next_event);
> >  fin:
> >  	return skb;
> >
> >
> >   
> 
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