[PATCH V2 2/2] rbtree_latch: don't need to check seq when it found a node

[Lai Jiangshan]

latch_tree_find() should be protected by caller via RCU or so.
When it find a node in an attempt, the node must be a valid one
in RCU's point's of view even the tree is (being) updated with a
new node with the same key which is entirely subject to timing
anyway.

Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 include/linux/rbtree_latch.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rbtree_latch.h b/include/linux/rbtree_latch.h
index 638942f53c0a..affc4b026d9b 100644
--- a/include/linux/rbtree_latch.h
+++ b/include/linux/rbtree_latch.h
@@ -245,7 +245,7 @@ latch_tree_find(void *key, struct latch_tree_root *root,
 	do {
 		seq = raw_read_seqcount_latch(&root->seq);
 		node = __lt_find(key, root, seq & 1, ops->comp);
-	} while (read_seqcount_retry(&root->seq, seq));
+	} while (!node && read_seqcount_retry(&root->seq, seq));
 
 	return node;
 }
-- 
2.20.1