aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorOleg Nesterov <oleg@redhat.com>2013-07-08 14:24:18 -0700
committerAl Viro <viro@zeniv.linux.org.uk>2013-07-13 13:29:24 +0400
commitfb4214db50b00558cc6e274c88b3f7325068e942 (patch)
tree17a68a322310eaeb5bd3c3885ccdd14191f8b7bd
parent4f5e65a1cc90bbb15b9f6cdc362922af1bcc155a (diff)
downloadlinux-fb4214db50b00558cc6e274c88b3f7325068e942.tar.gz
llist: fix/simplify llist_add() and llist_add_batch()
1. This is mostly theoretical, but llist_add*() need ACCESS_ONCE(). Otherwise it is not guaranteed that the first cmpxchg() uses the same value for old_entry and new_last->next. 2. These helpers cache the result of cmpxchg() and read the initial value of head->first before the main loop. I do not think this makes sense. In the likely case cmpxchg() succeeds, otherwise it doesn't hurt to reload head->first. I think it would be better to simplify the code and simply read ->first before cmpxchg(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrey Vagin <avagin@openvz.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: David Howells <dhowells@redhat.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--include/linux/llist.h19
-rw-r--r--lib/llist.c15
2 files changed, 12 insertions, 22 deletions
diff --git a/include/linux/llist.h b/include/linux/llist.h
index a5199f6d0e8..3e2b969d68f 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -151,18 +151,13 @@ static inline struct llist_node *llist_next(struct llist_node *node)
*/
static inline bool llist_add(struct llist_node *new, struct llist_head *head)
{
- struct llist_node *entry, *old_entry;
-
- entry = head->first;
- for (;;) {
- old_entry = entry;
- new->next = entry;
- entry = cmpxchg(&head->first, old_entry, new);
- if (entry == old_entry)
- break;
- }
-
- return old_entry == NULL;
+ struct llist_node *first;
+
+ do {
+ new->next = first = ACCESS_ONCE(head->first);
+ } while (cmpxchg(&head->first, first, new) != first);
+
+ return !first;
}
/**
diff --git a/lib/llist.c b/lib/llist.c
index 4a15115e90f..4a70d120138 100644
--- a/lib/llist.c
+++ b/lib/llist.c
@@ -39,18 +39,13 @@
bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
struct llist_head *head)
{
- struct llist_node *entry, *old_entry;
+ struct llist_node *first;
- entry = head->first;
- for (;;) {
- old_entry = entry;
- new_last->next = entry;
- entry = cmpxchg(&head->first, old_entry, new_first);
- if (entry == old_entry)
- break;
- }
+ do {
+ new_last->next = first = ACCESS_ONCE(head->first);
+ } while (cmpxchg(&head->first, first, new_first) != first);
- return old_entry == NULL;
+ return !first;
}
EXPORT_SYMBOL_GPL(llist_add_batch);