From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [Bugme-new] [Bug 39372] New: Problems with HFSC Scheduler
Date: Fri, 29 Jul 2011 15:27:40 +0200
Message-ID: <1311946060.2843.15.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
References: <bug-39372-10286@https.bugzilla.kernel.org/>
	 <20110714151425.844b7738.akpm@linux-foundation.org>
	 <4E32A796.8060104@ziu.info>
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Cc: Andrew Morton <akpm@linux-foundation.org>, netdev@vger.kernel.org,
	bugme-daemon@bugzilla.kernel.org,
	Jamal Hadi Salim <hadi@cyberus.ca>, lucas.bocchi@gmail.com,
	Patrick McHardy <kaber@trash.net>, 631945@bugs.debian.org,
	00bormoj@gmail.com, fdelawarde@wirelessmundi.com
To: Michal Soltys <soltys@ziu.info>
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Le vendredi 29 juillet 2011 =C3=A0 14:29 +0200, Michal Soltys a =C3=A9c=
rit :
> On 11-07-15 00:14, Andrew Morton wrote:
> >=20
> > (switched to email.  Please respond via emailed reply-to-all, not v=
ia
> > the bugzilla web interface).
> >=20
> >=20
> > Here: WARN_ON(next_time =3D=3D 0);
> >=20
>=20
> From the other thread on netfilter-devel:
>=20
> > 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:
> >=20
> > commit b262a5da755cc6ed0cb4fba230cd9bf4037e1096 sch_sfq: fix peek()
> > implementation
> >=20
> > and
> >=20
> > commit 9df49f2bfe862573911a080c75a6d81113c5c81d sch_sfq: avoid givi=
ng
> > spurious NET_XMIT_CN signals
> >=20
> > Reverting these patches makes HFSC work again.
> >=20
>=20
> This one (upstream 8efa885406359af300d46910642b50ca82c0fe47) seems to=
 be
> the culprit (does reverting only that one cures the problem ?)
>=20
> It allows SFQ to return success on enqueuing, when the packet really
> replaced some other packet in some other flow. This confuses outer qd=
isc
> (in this particular case HFSC) which thinks new packet was actually
> added each time such situation happes.
>=20

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.
>=20

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

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