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 <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andrey Vagin <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: David Howells <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Al Viro <[email protected]>

0 files changed, 0 insertions, 0 deletions