Re: [PATCH net-next v4 10/15] net/sched: act_mirred: Move the recursion counter struct netdev_xmit

[Juri Lelli <juri.lelli@redhat.com>]

On 15/05/25 11:55, Paolo Abeni wrote:
> CC sched maintainers.
> 
> On 5/12/25 11:27 AM, Sebastian Andrzej Siewior wrote:
> > mirred_nest_level 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.
> > 
> > Move mirred_nest_level to struct netdev_xmit as u8, provide wrappers.
> > 
> > Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> > Cc: Cong Wang <xiyou.wangcong@gmail.com>
> > Cc: Jiri Pirko <jiri@resnulli.us>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  include/linux/netdevice_xmit.h |  3 +++
> >  net/sched/act_mirred.c         | 28 +++++++++++++++++++++++++---
> >  2 files changed, 28 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/linux/netdevice_xmit.h b/include/linux/netdevice_xmit.h
> > index 38325e0702968..848735b3a7c02 100644
> > --- a/include/linux/netdevice_xmit.h
> > +++ b/include/linux/netdevice_xmit.h
> > @@ -8,6 +8,9 @@ struct netdev_xmit {
> >  #ifdef CONFIG_NET_EGRESS
> >  	u8  skip_txqueue;
> >  #endif
> > +#if IS_ENABLED(CONFIG_NET_ACT_MIRRED)
> > +	u8 sched_mirred_nest;
> > +#endif
> >  };
> 
> The above struct is embedded into task_struct in RT build. The new field
>  *should* use an existing hole. According to my weak knowledge in that
> area the task_struct binary layout is a critical, an explicit ack from
> SMEs would be nice.

Agree. Still fitting in an existing task_struct hole.

Reviewed-by: Juri Lelli <juri.lelli@redhat.com>

Best,
Juri