Re: [PATCH v2 3/5] tree/nocb: Adjust RCU_NOCB_WAKE_* macros from weaker to stronger

[Joel Fernandes]

On Tue, Aug 29, 2023 at 6:53 AM Frederic Weisbecker <frederic@xxxxxxxxxx> wrote:
>
> On Sat, Jul 29, 2023 at 02:27:33PM +0000, Joel Fernandes (Google) wrote:
> > This is needed to make the next patch work correctly as we rely on the
> > strength of the wakeup when comparing deferred-wakeup types across
> > different CPUs.
> >
> > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > ---
> >  kernel/rcu/tree.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> > index 192536916f9a..0f40a9c2b78d 100644
> > --- a/kernel/rcu/tree.h
> > +++ b/kernel/rcu/tree.h
> > @@ -288,8 +288,8 @@ struct rcu_data {
> >
> >  /* Values for nocb_defer_wakeup field in struct rcu_data. */
> >  #define RCU_NOCB_WAKE_NOT    0
> > -#define RCU_NOCB_WAKE_BYPASS 1
> > -#define RCU_NOCB_WAKE_LAZY   2
> > +#define RCU_NOCB_WAKE_LAZY   1
> > +#define RCU_NOCB_WAKE_BYPASS 2
> >  #define RCU_NOCB_WAKE                3
> >  #define RCU_NOCB_WAKE_FORCE  4
>
> Good change but make sure to audit all the occurences of
> RCU_NOCB_WAKE_LAZY and RCU_NOCB_WAKE_BYPASS. For example this breaks
> do_nocb_deferred_wakeup_timer() that will now ignore RCU_NOCB_WAKE_LAZY
> timers.
>

Ah I did do an audit, but missed this one. So then I think
do_nocb_deferred_wakeup_timer() should pass the weakest one
(RCU_NOCB_WAKE_LAZY) to do_nocb_deferred_wakeup_common().

Thanks a lot Frederic! I will take a deeper dive into this and author
users of RCU_NOCB_WAKE* and repost soon.

 - Joel