netdev - Re: [PATCH net] netlink: mmap: fix status setting in skb destructor

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Message-Id: <20150825.202203.408221873735724462.davem@davemloft.net>
Date:	Tue, 25 Aug 2015 20:22:03 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	chamaken@...il.com
Cc:	netdev@...r.kernel.org, daniel@...earbox.net, fw@...len.de
Subject: Re: [PATCH net] netlink: mmap: fix status setting in skb destructor

From: Ken-ichirou MATSUZAWA <chamaken@...il.com>
Date: Thu, 20 Aug 2015 16:07:33 +0900

> I don't know the intension of setting VALID status in the skb
> destructor. But I think it need to be set UNUSED status in case of
> error then release skb, or rx ring might be filled with RESERVED
> frames.
> 
> Signed-off-by: Ken-ichirou MATSUZAWA <chamas@...dion.ne.jp>

I think the idea is to have the user process this "zero length" frame
and advance the status itself.

I think it is probably racy and problematic to have the kernel set a
frame's state to UNUSED.  It is not a valid state transition for the
kernel side of RX ring processing.

Only the user can safely release ring entries back to the kernel.

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