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Subject[PATCH v8 5/6] rcu/tree: segcblist: Remove redundant smp_mb()s
Date
This memory barrier is not needed as rcu_segcblist_add_len() already
includes a memory barrier *before* the length of the list is updated.

Same reasoning for rcu_segcblist_enqueue().

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
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
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