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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH][net-next] openvswitch: change the data type of error
 status to atomic_long_t
Date: Sun, 07 Sep 2014 16:17:20 -0700 (PDT)
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From: Li RongQing <roy.qing.li@gmail.com>
Date: Sun, 7 Sep 2014 17:24:11 +0800

> 2.  I did not find that tx_dropped/tx_error/.. is protected by spin
> lock under net dir,
> sometime tx_dropped is atomic_long_t; sometime it is percpu variable;
> sometime it is
> u64,but does not need to protect.

If it is only modified in ->ndo_start_xmit() then it is protected by
the per-queue TX lock, as ->ndo_start_xmit() is always invoked with
it held (except in LLTX drivers of course).