On 4/30/23 12:25, Paolo Bonzini wrote:
Use a store-release when enqueuing a new call_rcu, and a load-acquire when dequeuing; and read the tail after checking that node->next is consistent, which is the standard message passing pattern and it is clearer than mb_read/mb_set.Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> --- util/rcu.c | 38 +++++++++++++++++++++++++++----------- 1 file changed, 27 insertions(+), 11 deletions(-) diff --git a/util/rcu.c b/util/rcu.c index e5b6e52be6f8..867607cd5a1e 100644 --- a/util/rcu.c +++ b/util/rcu.c @@ -189,8 +189,22 @@ static void enqueue(struct rcu_head *node) struct rcu_head **old_tail;node->next = NULL;+ + /* + * Make this node the tail of the list. The node will be + * used by further enqueue operations, but it will not + * be dequeued yet... + */ old_tail = qatomic_xchg(&tail, &node->next); - qatomic_mb_set(old_tail, node); + + /* + * ... until it is pointed to from another item in the list. + * In the meanwhile, try_dequeue() will find a NULL next pointer
Either "In the meantime" or "Meanwhile" (noun vs adverb). E.g. "Meanwhile, at Try Dequeue's volcano lair..." :-)
+ /* If the head node has NULL in its next pointer, the value is + * wrong and we need to wait until its enqueuer finishes the update. + */
/* * */ I know surrounding code is different, but slowly it will all be edited. Reviewed-by: Richard Henderson <richard.hender...@linaro.org> r~
