netdev - Re: [Bugme-new] [Bug 39372] New: Problems with HFSC Scheduler

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Message-ID: <1311946060.2843.15.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Fri, 29 Jul 2011 15:27:40 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michal Soltys <soltys@....info>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	bugme-daemon@...zilla.kernel.org,
	Jamal Hadi Salim <hadi@...erus.ca>, lucas.bocchi@...il.com,
	Patrick McHardy <kaber@...sh.net>, 631945@...s.debian.org,
	00bormoj@...il.com, fdelawarde@...elessmundi.com
Subject: Re: [Bugme-new] [Bug 39372] New: Problems with HFSC Scheduler

Le vendredi 29 juillet 2011 à 14:29 +0200, Michal Soltys a écrit :
> On 11-07-15 00:14, Andrew Morton wrote:
> > 
> > (switched to email.  Please respond via emailed reply-to-all, not via
> > the bugzilla web interface).
> > 
> > 
> > Here: WARN_ON(next_time == 0);
> > 
> 
> From the other thread on netfilter-devel:
> 
> > On 11-07-22 11:58, Michal Pokrywka wrote: After bisecting 2.6.39.1 it
> > turned out that the bug is caused independently by two patches:
> > 
> > commit b262a5da755cc6ed0cb4fba230cd9bf4037e1096 sch_sfq: fix peek()
> > implementation
> > 
> > and
> > 
> > commit 9df49f2bfe862573911a080c75a6d81113c5c81d sch_sfq: avoid giving
> > spurious NET_XMIT_CN signals
> > 
> > Reverting these patches makes HFSC work again.
> > 
> 
> This one (upstream 8efa885406359af300d46910642b50ca82c0fe47) seems to be
> the culprit (does reverting only that one cures the problem ?)
> 
> It allows SFQ to return success on enqueuing, when the packet really
> replaced some other packet in some other flow. This confuses outer qdisc
> (in this particular case HFSC) which thinks new packet was actually
> added each time such situation happes.
> 

Technically speaking, _this_ packet was successfuly enqueued.

Returning NET_XMIT_CN or NET_XMIT_SUCCESS should not trigger a bug in
caller.

> This in turn causes additional dequeues and ends with attempt
> to schedule non-existent packets, and triggers the warning.
> 

Then its probably a bug in HFSC : It doesnt understand SFQ lost a
packet.

I'll take a look, thanks for the report.



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