From 4c747e86cda5d7eab46390779447f216ce9aa5de Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Thu, 28 Feb 2019 15:05:53 +0100 Subject: [PATCH] MINOR: list: make the delete and pop operations idempotent These operations previously used to return a "locked" element, which is a constraint when multiple threads try to delete the same element, because the second one will block indefinitely. Instead, let's make sure that both LIST_DEL_LOCKED() and LIST_POP_LOCKED() always reinitialize the element after deleting it. This ensures that the second thread will immediately unblock and succeed with the removal. It also secures the pop vs delete competition that may happen when trying to remove an element that's about to be dequeued. --- include/common/mini-clist.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/common/mini-clist.h b/include/common/mini-clist.h index d8fcb1599..3b1f599ca 100644 --- a/include/common/mini-clist.h +++ b/include/common/mini-clist.h @@ -261,6 +261,9 @@ struct cond_wordlist { n->p = p; \ p->n = n; \ __ha_barrier_store(); \ + (el)->p = (el); \ + (el)->n = (el); \ + __ha_barrier_store(); \ break; \ } \ } while (0) @@ -308,6 +311,9 @@ struct cond_wordlist { (lh)->n = n2; \ (n2)->p = (lh); \ __ha_barrier_store(); \ + (n)->p = (n); \ + (n)->n = (n); \ + __ha_barrier_store(); \ _ret = LIST_ELEM(n, pt, el); \ break; \ } \