tty: Use lockless flip buffer free list
In preparation for lockless flip buffers, make the flip buffer
free list lockless.
NB: using llist is not the optimal solution, as the driver and
buffer work may contend over the llist head unnecessarily. However,
test measurements indicate this contention is low.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/llist.h b/include/linux/llist.h
index cdaa7f0..8828a78 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -125,6 +125,29 @@
(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
/**
+ * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
+ * safe against removal of list entry
+ * @pos: the type * to use as a loop cursor.
+ * @n: another type * to use as temporary storage
+ * @node: the first entry of deleted list entries.
+ * @member: the name of the llist_node with the struct.
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being removed from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry. If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each_entry_safe(pos, n, node, member) \
+ for (pos = llist_entry((node), typeof(*pos), member); \
+ &pos->member != NULL && \
+ (n = llist_entry(pos->member.next, typeof(*n), member), true); \
+ pos = n)
+
+/**
* llist_empty - tests whether a lock-less list is empty
* @head: the list to test
*