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Date:   Fri, 08 Dec 2017 13:08:48 -0500 (EST)
From:   David Miller <>
Subject: Re: [PATCH] ptr_ring: add barriers

From: "Michael S. Tsirkin" <>
Date: Tue, 5 Dec 2017 21:29:37 +0200

> Users of ptr_ring expect that it's safe to give the
> data structure a pointer and have it be available
> to consumers, but that actually requires an smb_wmb
> or a stronger barrier.
> In absence of such barriers and on architectures that reorder writes,
> consumer might read an un=initialized value from an skb pointer stored
> in the skb array.  This was observed causing crashes.
> To fix, add memory barriers.  The barrier we use is a wmb, the
> assumption being that producers do not need to read the value so we do
> not need to order these reads.
> Reported-by: George Cherian <>
> Suggested-by: Jason Wang <>
> Signed-off-by: Michael S. Tsirkin <>
> ---
> George, could you pls report whether this patch fixes
> the issue for you?
> This seems to be needed in stable as well.

I really need some testing feedback for this before I apply it
and queue it up for -stable.


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