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Date: Thu, 8 Sep 2016 22:48:12 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Cong Wang <xiyou.wangcong@...il.com> Cc: Eric Dumazet <eric.dumazet@...il.com>, David Miller <davem@...emloft.net>, Linux Kernel Network Developers <netdev@...r.kernel.org>, Jamal Hadi Salim <jhs@...atatu.com>, John Fastabend <john.fastabend@...il.com>, Hadar Hen Zion <hadarh@...lanox.com>, Amir Vadai <amirva@...lanox.com> Subject: Re: [PATCH net] net_sched: act_mirred: full rcu conversion On Thu, Sep 08, 2016 at 10:24:32PM -0700, Cong Wang wrote: > On Thu, Sep 8, 2016 at 8:35 AM, Eric Dumazet <eric.dumazet@...il.com> wrote: > > From: Eric Dumazet <edumazet@...gle.com> > > > > As reported by Cong Wang, I was lazy when I did initial RCU conversion > > of tc_mirred, as I thought I could avoid allocation/freeing of a > > parameter block. > > Quote from Eric Dumazet: > > https://www.mail-archive.com/netdev@vger.kernel.org/msg115482.html > > <Quote> > Well, I added a READ_ONCE() to read tcf_action once. > > Adding rcu here would mean adding a pointer and extra cache line, to > deref the values. > > IMHO the race here has no effect . You either read the old or new value. > </Quote> > > Me with facepalm... ;-) imo the deliberate small race in Eric's initial lock removal in mirred was a good design choice. I think he did this patch only to silence the complains with the code instead of arguing with words. imo the initial code is good as-is. This patch is also a nice improvement, but certainly not mandatory. 'face palm' is unnecessary.
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