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

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 <redacted>
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