netdev - Re: [PATCH net-next-2.6] sfq: fix slot_dequeue

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Message-ID: <20101230174918.GA2018@del.dom.local>
Date:	Thu, 30 Dec 2010 18:49:18 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] sfq: fix slot_dequeue_head()

On Thu, Dec 30, 2010 at 04:02:48PM +0100, Eric Dumazet wrote:
> Le mercredi 22 décembre 2010 ?? 07:32 +0000, Jarek Poplawski a écrit :
> > > Also, slot_dequeue_tail() should make sure slot skb chain is correctly
> > > terminated, or sfq_dump_class_stats() can access freed skbs.
> > 
> > ...and a good hint for code reusing ;-)
> 
> Yes, and of course same fix is needed in slot_dequeue_head(), as further
> testing on my side made it pretty clear.
> 
> I was adding possibility to have more packets queued in SFQ (more
> packets than max number of flows) and got unexpected crashes.
> 
> Reverting to net-next-2.6, I still got crashes. Oops.
> 
> [PATCH net-next-2.6] sfq: fix slot_dequeue_head()
> 
> slot_dequeue_head() should make sure slot skb chain is correct in both
> ways, or we can crash if all possible flows are in use.

Nice scenario ;-) Of course, it's easy to guess I looked for something
like this after your previous fix and missed that :-| Btw, it looks
like slot_queue_init() could go back to sfq_init() now.

Jarek P.

> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Jarek Poplawski <jarkao2@...il.com>
> ---
>  net/sched/sch_sfq.c |    1 +
>  1 files changed, 1 insertion(+)
> 
> diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> index 6a2f88f..3977e56 100644
> --- a/net/sched/sch_sfq.c
> +++ b/net/sched/sch_sfq.c
> @@ -292,6 +292,7 @@ static inline struct sk_buff *slot_dequeue_head(struct sfq_slot *slot)
>  	struct sk_buff *skb = slot->skblist_next;
>  
>  	slot->skblist_next = skb->next;
> +	skb->next->prev = (struct sk_buff *)slot;
>  	skb->next = skb->prev = NULL;
>  	return skb;
>  }
> 
> 
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