netdev - Re: [Patch net-next] net_sched: remove the unsafe __skb_array

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Date:   Tue, 02 Jan 2018 11:37:27 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, jakub.kicinski@...ronome.com,
        john.fastabend@...il.com
Subject: Re: [Patch net-next] net_sched: remove the unsafe
 __skb_array_empty()

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Thu, 21 Dec 2017 16:03:30 -0800

> __skb_array_empty() is only safe if array is never resized.
> pfifo_fast_dequeue() is called in TX BH context and without
> qdisc lock, so even after we disable BH on ->reset() path
> we can still race with other CPU's.
> 
> Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
> Reported-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Cc: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

Based upon the discussion over this patch, this bug is ultimately fixed
by John's patch which adds a dummy element at the end of allocated
ptr_ring queues.

And I've just applied that.