On Thu, 27 Aug 2020 00:25:31 -0700 Eric Dumazet wrote:
> On 8/26/20 12:40 PM, Jakub Kicinski wrote:
> > To ensure memory ordering is correct we need to use RCU accessors.
>
> > + set_bit(NAPI_STATE_NPSVC, &napi->state);
> > + list_add_rcu(&napi->dev_list, &dev->napi_list);
>
> >
> > - list_for_each_entry(napi, &dev->napi_list, dev_list) {
> > + list_for_each_entry_rcu(napi, &dev->napi_list, dev_list) {
> > if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) {
> > poll_one_napi(napi);
> > smp_store_release(&napi->poll_owner, -1);
> >
>
> You added rcu in this patch (without anything in the changelog).
I mentioned I need it for the barriers, in particular I wanted the
store release barrier in list_add. Not extremely clean :(
> netpoll_poll_dev() uses rcu_dereference_bh(), suggesting you might
> need list_for_each_entry_rcu_bh()
I thought the RCU flavors are mostly meaningless at this point,
list_for_each_entry_rcu() checks rcu_read_lock_any_held(). I can add
the definition of list_for_each_entry_rcu_bh() (since it doesn't exist)
or go back to non-RCU iteration (since the use is just documentation,
the code is identical). Or fix it some other way?
