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

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Date:	Tue, 3 Jan 2012 08:25:57 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Luigi Rizzo <rizzo@....unipi.it>
Cc:	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()

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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