On Thu, Jul 16, 2020 at 07:16:24PM -0700, Alexei Starovoitov wrote: > On Fri, Jul 17, 2020 at 01:06:07AM +0200, Daniel Borkmann wrote: > > > + ret = bpf_arch_text_poke(poke->tailcall_bypass, > > > + BPF_MOD_JUMP, > > > + NULL, bypass_addr); > > > + BUG_ON(ret < 0 && ret != -EINVAL); > > > + /* let other CPUs finish the execution of program > > > + * so that it will not possible to expose them > > > + * to invalid nop, stack unwind, nop state > > > + */ > > > + synchronize_rcu(); > > > > Very heavyweight that we need to potentially call this /multiple/ times for just a > > /single/ map update under poke mutex even ... but agree it's needed here to avoid > > racing. :( > > Yeah. I wasn't clear with my suggestion earlier. > I meant to say that synchronize_rcu() can be done between two loops. > list_for_each_entry(elem, &aux->poke_progs, list) > for (i = 0; i < elem->aux->size_poke_tab; i++) > bpf_arch_text_poke(poke->tailcall_bypass, ... > synchronize_rcu(); > list_for_each_entry(elem, &aux->poke_progs, list) > for (i = 0; i < elem->aux->size_poke_tab; i++) > bpf_arch_text_poke(poke->poke->tailcall_target, ... > > Not sure how much better it will be though. > text_poke is heavy. > I think it's heavier than synchronize_rcu(). > Long term we can do batch of text_poke-s. Yeah since we introduce another poke target we could come up with preparing the vector of pokes as you're saying? > > I'm actually fine with above approach of synchronize_rcu() without splitting the loop. > This kind of optimizations can be done later as a follow up. > I'd really like to land this stuff in this bpf-next cycle. > It's a big improvement to tail_calls and bpf2bpf calls.
