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

[Vlastimil Babka]

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"?

> 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.

> Apply the change to
> SLAB_TYPESAFE_BY_RCU example code snippet, too.
> 
> Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
> ---
>  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();