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Date:	Mon, 21 Apr 2014 16:28:39 -0700
From:	Cong Wang <>
To:	Jamal Hadi Salim <>
Cc:	Linux Kernel Network Developers <>,
	"David S. Miller" <>,
	Cong Wang <>
Subject: Re: [Patch net] sched, cls: check if we could overwrite actions when
 changing a filter

On Sat, Apr 19, 2014 at 4:10 AM, Jamal Hadi Salim <> wrote:
> On 04/18/14 13:18, Cong Wang wrote:
>> IOW, what's wrong with changing if (icmp) { A } to if (icmp) { B } ?
>> where A and B could be any complex combination of actions.
>> RTNL lock guarantees this is transactional.
> RTNL is one dimension. The other is the datapath processing.
> You need to make sure that packets still flow correctly during the
> change over.

Sure, since we grab tcf_tree_lock() before changing actions in
tcf_exts_change(), I think this is guaranteed too.

>> I never mean to only add or remove one of them inside, although
>> my specific case is just for appending, my patch should allow to
>> overwrite all the actions together.
> Well - then go nuts and put out a patch.
> Replace _all or none_ is a reasonable approach.

Great! We both agree on this.

Looking at the current code, we first initialize a list of actions
and then replace them as a whole by splicing the lists with
tcf_tree_lock held, so this is already done. IOW, this patch
is enough.

Or am I missing anything?

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