From 2e6070d0f3c445476172dda329ae5d2a981a4986 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Wed, 30 Sep 2009 09:21:49 -0400 Subject: [PATCH] urcu-ht: fix del node race Signed-off-by: Mathieu Desnoyers --- urcu-ht.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/urcu-ht.c b/urcu-ht.c index 0bbdb5d..a26878f 100644 --- a/urcu-ht.c +++ b/urcu-ht.c @@ -134,10 +134,12 @@ restart: /* * Restart until we successfully remove the entry, or no entry is left * ((void *)(unsigned long)-ENOENT). + * Deal with concurrent stealers by verifying that there are no element + * in the list still pointing to the element stolen. (del_node) */ void *ht_steal(struct rcu_ht *ht, void *key) { - struct rcu_ht_node **prev, *node; + struct rcu_ht_node **prev, *node, *del_node = NULL; unsigned long hash; void *data; @@ -150,8 +152,12 @@ retry: node = rcu_dereference(*prev); for (;;) { if (likely(!node)) { - data = (void *)(unsigned long)-ENOENT; - goto error; + if (del_node) { + goto end; + } else { + data = (void *)(unsigned long)-ENOENT; + goto error; + } } if (node->key == key) { break; @@ -161,9 +167,14 @@ retry: } /* Found it ! pointer to object is in "prev" */ if (rcu_cmpxchg_pointer(prev, node, node->next) != node) - goto restart; + del_node = node; + goto restart; - /* From that point, we own node. We can free it outside of read lock */ +end: + /* + * From that point, we own node. Note that there can still be concurrent + * RCU readers using it. We can free it outside of read lock after a GP. + */ rcu_read_unlock(); data = node->data; -- 2.34.1