65;6003;1cOn Wed, Oct 21, 2020 at 03:08:12PM -0400, Joel Fernandes (Google) wrote:
> This memory barrier is not needed as rcu_segcblist_add_len() already
> includes a memory barrier *before* the length of the list is updated.
*before* and *after*.
As you have both cases below.
Thanks
>
> Same reasoning for rcu_segcblist_enqueue().
>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> kernel/rcu/rcu_segcblist.c | 1 -
> kernel/rcu/tree.c | 1 -
> 2 files changed, 2 deletions(-)
>
> diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
> index 19ff82b805fb..f0fcdf9d0f7f 100644
> --- a/kernel/rcu/rcu_segcblist.c
> +++ b/kernel/rcu/rcu_segcblist.c
> @@ -268,7 +268,6 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
> struct rcu_head *rhp)
> {
> rcu_segcblist_inc_len(rsclp);
> - smp_mb(); /* Ensure counts are updated before callback is enqueued. */
> rcu_segcblist_inc_seglen(rsclp, RCU_NEXT_TAIL);
> rhp->next = NULL;
> WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp);
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 346a05506935..6c6d3c7036e6 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2525,7 +2525,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
>
> /* Update counts and requeue any remaining callbacks. */
> rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
> - smp_mb(); /* List handling before counting for rcu_barrier(). */
> rcu_segcblist_add_len(&rdp->cblist, -count);
>
> /* Reinstate batch limit if we have worked down the excess. */
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>
