Re: [PATCH net-next 06/18] netfilter: nf_dup{4, 6}: Move duplication check to task_struct.

[Paolo Abeni <pabeni@redhat.com>]

Hi,

On 3/9/25 3:46 PM, Sebastian Andrzej Siewior wrote:
> nf_skb_duplicated is a per-CPU variable and relies on disabled BH for its
> locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
> this data structure requires explicit locking.
> 
> Due to the recursion involved, the simplest change is to make it a
> per-task variable.
> 
> Move the per-CPU variable nf_skb_duplicated to task_struct and name it
> in_nf_duplicate. Add it to the existing bitfield so it doesn't use
> additional memory.
> 
> Cc: Pablo Neira Ayuso <pablo@netfilter.org>
> Cc: Jozsef Kadlecsik <kadlec@netfilter.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

I'm not a super-fan of adding more flags to 'struct task', but in this
specific case I agree is the better option, as otherwise we should
acquire the local lock for a relatively large scope - the whole packet
processing by nft, right?

Still this needs some explicit ack from the relevant maintainers.
@Peter, @Juri, @Valentin: could you please have a look?

Thanks!

Paolo