netdev - Re: [net-next v2 1/1] tipc: clean up skb list lock handling on send path

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Message-Id: <20190818.140121.879479854866287427.davem@davemloft.net>
Date:   Sun, 18 Aug 2019 14:01:21 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jon.maloy@...csson.com
Cc:     netdev@...r.kernel.org, tung.q.nguyen@...tech.com.au,
        hoang.h.le@...tech.com.au, lxin@...hat.com, shuali@...hat.com,
        ying.xue@...driver.com, edumazet@...gle.com,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [net-next v2 1/1] tipc: clean up skb list lock handling on
 send path

From: Jon Maloy <jon.maloy@...csson.com>
Date: Thu, 15 Aug 2019 16:42:50 +0200

> The policy for handling the skb list locks on the send and receive paths
> is simple.
> 
> - On the send path we never need to grab the lock on the 'xmitq' list
>   when the destination is an exernal node.
> 
> - On the receive path we always need to grab the lock on the 'inputq'
>   list, irrespective of source node.
> 
> However, when transmitting node local messages those will eventually
> end up on the receive path of a local socket, meaning that the argument
> 'xmitq' in tipc_node_xmit() will become the 'ínputq' argument in  the
> function tipc_sk_rcv(). This has been handled by always initializing
> the spinlock of the 'xmitq' list at message creation, just in case it
> may end up on the receive path later, and despite knowing that the lock
> in most cases never will be used.
> 
> This approach is inaccurate and confusing, and has also concealed the
> fact that the stated 'no lock grabbing' policy for the send path is
> violated in some cases.
> 
> We now clean up this by never initializing the lock at message creation,
> instead doing this at the moment we find that the message actually will
> enter the receive path. At the same time we fix the four locations
> where we incorrectly access the spinlock on the send/error path.
> 
> This patch also reverts commit d12cffe9329f ("tipc: ensure head->lock
> is initialised") which has now become redundant.
> 
> CC: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> Acked-by: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied.