netdev - Re: [PATCH net] net: lwtunnel: fix recursion loops

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Message-ID: <87v7seh1cw.fsf@toke.dk>
Date: Wed, 12 Mar 2025 13:36:47 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Justin Iurman <justin.iurman@...ege.be>, netdev@...r.kernel.org
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, horms@...nel.org, Roopa Prabhu <roopa@...dia.com>,
 Andrea Mayer <andrea.mayer@...roma2.it>, Stefano Salsano
 <stefano.salsano@...roma2.it>, Ahmed Abdelsalam <ahabdels.dev@...il.com>,
 Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net] net: lwtunnel: fix recursion loops

Justin Iurman <justin.iurman@...ege.be> writes:

> On 3/12/25 13:29, Toke Høiland-Jørgensen wrote:
>> Justin Iurman <justin.iurman@...ege.be> writes:
>> 
>>>> --- /dev/null
>>>> +++ b/net/core/lwtunnel.h
>>>> @@ -0,0 +1,42 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>>> +#ifndef _NET_CORE_LWTUNNEL_H
>>>> +#define _NET_CORE_LWTUNNEL_H
>>>> +
>>>> +#include <linux/netdevice.h>
>>>> +
>>>> +#define LWTUNNEL_RECURSION_LIMIT 8
>>>> +
>>>> +#ifndef CONFIG_PREEMPT_RT
>>>> +static inline bool lwtunnel_recursion(void)
>>>> +{
>>>> +	return unlikely(__this_cpu_read(softnet_data.xmit.recursion) >
>>>> +			LWTUNNEL_RECURSION_LIMIT);
>>>> +}
>>>> +
>>>> +static inline void lwtunnel_recursion_inc(void)
>>>> +{
>>>> +	__this_cpu_inc(softnet_data.xmit.recursion);
>>>> +}
>>>> +
>>>> +static inline void lwtunnel_recursion_dec(void)
>>>> +{
>>>> +	__this_cpu_dec(softnet_data.xmit.recursion);
>>>> +}
>>>> +#else
>>>> +static inline bool lwtunnel_recursion(void)
>>>> +{
>>>> +	return unlikely(current->net_xmit.recursion > LWTUNNEL_RECURSION_LIMIT);
>>>> +}
>>>> +
>>>> +static inline void lwtunnel_recursion_inc(void)
>>>> +{
>>>> +	current->net_xmit.recursion++;
>>>> +}
>>>> +
>>>> +static inline void lwtunnel_recursion_dec(void)
>>>> +{
>>>> +	current->net_xmit.recursion--;
>>>> +}
>>>> +#endif
>>>> +
>>>> +#endif /* _NET_CORE_LWTUNNEL_H */
>>>
>>> Wondering what folks think about the above idea to reuse fields that
>>> dev_xmit_recursion() currently uses. IMO, it seems OK considering the
>>> use case and context. If not, I guess we'd need to add a new field to
>>> both softnet_data and task_struct.
>> 
>> Why not just reuse the dev_xmit_recursion*() helpers directly?
>> 
>> -Toke
>> 
>
> It was my initial idea, but I'm not sure I can. Looks like they're not 
> exposed (it's a local .h in net/core/).

Well, code can be moved :)

Certainly, if you're going to re-implement the helpers with the same
underlying data structure, it's better to just move the existing ones
and reuse them.

-Toke