diff options
author | Oleg Nesterov <oleg@redhat.com> | 2013-07-08 23:24:18 +0200 |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-07-13 11:29:24 +0200 |
commit | fb4214db50b00558cc6e274c88b3f7325068e942 (patch) | |
tree | 17a68a322310eaeb5bd3c3885ccdd14191f8b7bd /lib/llist.c | |
parent | fput: turn "list_head delayed_fput_list" into llist_head (diff) | |
download | linux-fb4214db50b00558cc6e274c88b3f7325068e942.tar.xz linux-fb4214db50b00558cc6e274c88b3f7325068e942.zip |
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 '')
-rw-r--r-- | lib/llist.c | 15 |
1 files changed, 5 insertions, 10 deletions
diff --git a/lib/llist.c b/lib/llist.c index 4a15115e90f8..4a70d120138c 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); |