netdev - Re: act_mirred: remove spinlock in fast path

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Message-ID: <CANn89iK3DLjJ6y34y1=pnUmH0RKBwwQWj4ZzizVmm98BXxGxYA@mail.gmail.com>
Date:	Fri, 17 Jun 2016 15:03:54 -0700
From:	Eric Dumazet <edumazet@...gle.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: act_mirred: remove spinlock in fast path

On Fri, Jun 17, 2016 at 2:59 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:

> Generally speaking I worry about we change multiple fields in a struct
> meanwhile we could still read them any time in the middle, we may
> get them correct for some easy case, but it is hard to insure the
> correctness when the struct becomes large.
>
> I am thinking to make more tc actions lockless, so this problem
> comes up immediately for other complex cases than mirred.

I certainly wont object to a patch.

Also note that instead of RCU with a pointer and the usual kfree_rcu() stuff,
we now can use seqcount_latch infra which might allow to not increase
memory foot print.