From fb4214db50b00558cc6e274c88b3f7325068e942 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 8 Jul 2013 14:24:18 -0700 Subject: 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 Cc: Al Viro Cc: Andrey Vagin Cc: "Eric W. Biederman" Cc: David Howells Cc: Huang Ying Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Al Viro --- include/linux/llist.h | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) (limited to 'include/linux') diff --git a/include/linux/llist.h b/include/linux/llist.h index a5199f6d0e82..3e2b969d68f6 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; } /** -- cgit v1.2.3