Re: [PATCH v2 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

SeongJae Park
2023-04-17T17:27:05Z

Hi Vlastimil,

On Mon, 17 Apr 2023 13:05:40 +0200 Vlastimil Babka <vbabka@suse.cz> wrote:

> On 4/15/23 05:31, SeongJae Park wrote:
> > The SLAB_TYPESAFE_BY_RCU example code snippet is having not tiny RCU
>
> Since "tiny RCU" means something quite specific in the RCU world, it can be
> confusing to read it in this sense. We could say e.g. "... snippet uses a
> single RCU read-side critical section for retries"?

Looks much better, thank you for this suggestion!

>
> > read-side critical section. 'Documentation/RCU/rculist_nulls.rst' has
> > similar example code snippet, and commit da82af04352b ("doc: Update and
> > wordsmith rculist_nulls.rst") has broken it.
>
> "has broken it" has quite different meaning than "has broken it up" :) I
> guess we could just add the "up", unless someone has an even better wording.

Good point, thank you for your suggestion!

I will apply above suggestion on the next spin.

Thanks,
SJ

>
> > Apply the change to
> > SLAB_TYPESAFE_BY_RCU example code snippet, too.
> >
> > Signed-off-by: SeongJae Park <sj@kernel.org>
> > ---
> > include/linux/slab.h | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index b18e56c6f06c..6acf1b7c6551 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -53,16 +53,18 @@
> > * stays valid, the trick to using this is relying on an independent
> > * object validation pass. Something like:
> > *
> > + * begin:
> > * rcu_read_lock();
> > - * again:
> > * obj = lockless_lookup(key);
> > * if (obj) {
> > * if (!try_get_ref(obj)) // might fail for free objects
> > - * goto again;
> > + * rcu_read_unlock();
> > + * goto begin;
> > *
> > * if (obj->key != key) { // not the object we expected
> > * put_ref(obj);
> > - * goto again;
> > + * rcu_read_unlock();
> > + * goto begin;
> > * }
> > * }
> > * rcu_read_unlock();
>