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Subject[listll] Fix fetching of head->first in lockless lists.

The fetching of head->first must occur in the cmpxchg loop.

With the current code head->first may change after the content were assigned to
the "entry" variable. Entry then not be change anymore in the loop and be
used as old_entry for the cmpxchg. The cmpxchg will then therefore
compare "entry" to list->head. This will always fail if list->head has
changed. The restarting of the loop will not fetch head->first again. So
we could have a hang there.

I guess this only works now because the compiler optimizations pull
the fetching of head->first into the loop.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
lib/llist.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6/lib/llist.c
===================================================================
--- linux-2.6.orig/lib/llist.c 2011-08-04 09:34:30.000000000 -0500
+++ linux-2.6/lib/llist.c 2011-08-04 09:35:08.000000000 -0500
@@ -42,8 +42,8 @@ void llist_add(struct llist_node *new, s
BUG_ON(in_nmi());
#endif

- entry = head->first;
do {
+ entry = head->first;
old_entry = entry;
new->next = entry;
cpu_relax();
@@ -66,8 +66,8 @@ void llist_add_batch(struct llist_node *
BUG_ON(in_nmi());
#endif

- entry = head->first;
do {
+ entry = head->first;
old_entry = entry;
new_last->next = entry;
cpu_relax();
@@ -97,8 +97,8 @@ struct llist_node *llist_del_first(struc
BUG_ON(in_nmi());
#endif

- entry = head->first;
do {
+ entry = head->first;
if (entry == NULL)
return NULL;
old_entry = entry;

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