netdev - Re: [PATCH] sch_qfq: fix overflow in qfq_update

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Date:	Tue, 3 Jan 2012 17:54:22 +0100
From:	Luigi Rizzo <rizzo@....unipi.it>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Dave Taht <dave.taht@...il.com>
Subject: Re: [PATCH] sch_qfq: fix overflow in qfq_update_start()

thanks, appreciated.

cheers
luigi

On Tue, Jan 03, 2012 at 08:25:57AM -0800, Stephen Hemminger wrote:
> On Mon, 02 Jan 2012 16:47:57 +0100
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > grp->slot_shift is between 22 and 41, so using 32bit wide variables is
> > probably a typo.
> > 
> > This could explain QFQ hangs Dave reported to me, after 2^23 packets ?
> > 
> > (23 = 64 - 41)
> > 
> > Reported-by: Dave Taht <dave.taht@...il.com>
> > CC: Stephen Hemminger <shemminger@...tta.com>
> > CC: Dave Taht <dave.taht@...il.com>
> > ---
> >  net/sched/sch_qfq.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
> > index 1033434..7b03254 100644
> > --- a/net/sched/sch_qfq.c
> > +++ b/net/sched/sch_qfq.c
> > @@ -817,11 +817,11 @@ skip_unblock:
> >  static void qfq_update_start(struct qfq_sched *q, struct qfq_class *cl)
> >  {
> >  	unsigned long mask;
> > -	uint32_t limit, roundedF;
> > +	u64 limit, roundedF;
> >  	int slot_shift = cl->grp->slot_shift;
> >  
> >  	roundedF = qfq_round_down(cl->F, slot_shift);
> > -	limit = qfq_round_down(q->V, slot_shift) + (1UL << slot_shift);
> > +	limit = qfq_round_down(q->V, slot_shift) + (1ULL << slot_shift);
> >  
> >  	if (!qfq_gt(cl->F, q->V) || qfq_gt(roundedF, limit)) {
> >  		/* timestamp was stale */
> > 
> > 
> 
> 
> You need to copy the BSD developers on these patches since
> most of the code came from them and FreeBSD probably still has same bug!
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