diff options
author | Oleg Nesterov <oleg@redhat.com> | 2013-07-08 17:24:18 -0400 |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-07-13 05:29:24 -0400 |
commit | fb4214db50b00558cc6e274c88b3f7325068e942 (patch) | |
tree | 17a68a322310eaeb5bd3c3885ccdd14191f8b7bd /include | |
parent | 4f5e65a1cc90bbb15b9f6cdc362922af1bcc155a (diff) |
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>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/llist.h | 19 |
1 files changed, 7 insertions, 12 deletions
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) | |||
151 | */ | 151 | */ |
152 | static inline bool llist_add(struct llist_node *new, struct llist_head *head) | 152 | static inline bool llist_add(struct llist_node *new, struct llist_head *head) |
153 | { | 153 | { |
154 | struct llist_node *entry, *old_entry; | 154 | struct llist_node *first; |
155 | 155 | ||
156 | entry = head->first; | 156 | do { |
157 | for (;;) { | 157 | new->next = first = ACCESS_ONCE(head->first); |
158 | old_entry = entry; | 158 | } while (cmpxchg(&head->first, first, new) != first); |
159 | new->next = entry; | 159 | |
160 | entry = cmpxchg(&head->first, old_entry, new); | 160 | return !first; |
161 | if (entry == old_entry) | ||
162 | break; | ||
163 | } | ||
164 | |||
165 | return old_entry == NULL; | ||
166 | } | 161 | } |
167 | 162 | ||
168 | /** | 163 | /** |