On Thu, Mar 19, 2026 at 09:55:48AM +0100, Sebastian Andrzej Siewior wrote:
> On 2026-03-18 11:48:56 [-0700], Paul E. McKenney wrote:
> > We would need a lockless enqueue, which we have in llist.h.
>
> Only if CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. Otherwise you must not
> provide call_rcu_nmi().
I *think* that BPF is provided only in such architectures, so agreed.
> > The irq-work to actually do the call_rcu() or similar.
>
> reasonable.
>
> > There would also need to be rcu_barrier() changes, for example, to
> > drain all the llists.
> >
> > > I mean I am curious here who needs it any why ;)
> >
> > You got it right above, BPF. ;-)
> >
> > They currently check in_nmi() and to the irq-work step themselves.
>
> Then it would make sense since you do actually have users.
For more fun, they would like to attach BPF programs to call_rcu() and
call_srcu() internals, which would require a per-task recursion check.
Or perhaps some other trick.
Thanx, Paul
