linux-kernel - Re: [PATCH net-next] net: skbuff: Skip early return in skb

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Message-ID: <16add5c4-b1c2-4242-8b71-51332c3bae44@redhat.com>
Date: Tue, 30 Jul 2024 16:37:10 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Florian Westphal <fw@...len.de>, Breno Leitao <leitao@...ian.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 leit@...a.com, Chris Mason <clm@...com>,
 "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: skbuff: Skip early return in skb_unref when
 debugging

On 7/30/24 16:10, Jakub Kicinski wrote:
> On Tue, 30 Jul 2024 13:15:57 +0200 Paolo Abeni wrote:
>>> I was under impression that entire reason for CONFIG_DEBUG_NET was
>>> to enable more checks for fuzzers and the like, i.e. NOT for production
>>> kernels.
>>
>> I feel like I already had this discussion and I forgot the outcome, if
>> so I'm sorry. To me the "but is safe to select." part in the knob
>> description means this could be enabled in production, and AFAICS the
>> CONFIG_DEBUG_NET-enabled code so far respects that assumption.
> 
> I believe the previous discussion was page pool specific and there
> wasn't as much of a conclusion as an acquiescence (read: we had more
> important things on our minds than that argument ;)).
> 
> Should we set a bar for how much perf impact is okay?

I think that better specifying the general guidance/expectation should 
be enough. What about extending the knob description with something alike:
---
diff --git a/net/Kconfig.debug b/net/Kconfig.debug
index 5e3fffe707dd..058cf031913b 100644
--- a/net/Kconfig.debug
+++ b/net/Kconfig.debug
@@ -24,3 +24,5 @@ config DEBUG_NET
         help
           Enable extra sanity checks in networking.
           This is mostly used by fuzzers, but is safe to select.
+         This could introduce some very minimal overhead and
+         is not suggested for production systems.