netdev - Re: [PATCH net] net: sched: act_api: size RTM

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Message-ID: <CAM0EoMmY-v0HWAkB5EgSYhpca8fXVX7SQ1SpVbUBcFpbvuTd1g@mail.gmail.com>
Date: Fri, 30 Jan 2026 12:53:40 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Paul Moses <p@....org>
Cc: netdev@...r.kernel.org, xiyou.wangcong@...il.com, jiri@...nulli.us, 
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	horms@...nel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net] net: sched: act_api: size RTM_GETACTION reply by fill size

On Fri, Jan 30, 2026 at 12:22 PM Paul Moses <p@....org> wrote:
>
> Yes, In net/sched/act_api.c the GETACTION notify path always does alloc_skb(NLMSG_GOODSIZE), if tca_get_fill()
> runs out of tailroom it returns -1 and tcf_get_notify() maps that to -EINVAL. So failures are size-dependent
> and can look intermittent across different action dumps. act_gate might be the outlier?
>

Very bizarre that dump would fail because it is transactional. It
shouldnt matter that you are only allocing NLMSG_GOODSIZE.
Is there a possibility that  a single act_gate entry can be larger
than NLMSG_GOODSIZE?

> The size is already computed in tca_action_gd() (sum tcf_action_fill_size() then tcf_action_full_attrs_size())
> and add/del already allocate max(attr_size, NLMSG_GOODSIZE). This patch just makes GETACTION consistent with
> that.
>

I looked at act_gate dump and it is sane. Which leads to perhaps your
test program being bugy.

Install the 100 actions then use tc to count.
Something like:
 tc actions ls action gate | grep index | wc -l

cheers,
jamal

> On the reproducer: the gatebench test with 100 entries is reasonable.
> https://raw.githubusercontent.com/jopamo/gatebench/refs/heads/main/src/selftests/test_large_dump.c
>
> I plan to follow this up with another patch for act_gate and believe they both are integral to fully stabilize
> act_gate.
>
> Thanks
> Paul