diff --git a/[refs] b/[refs]
index dc0a77cc1041..d0240f9d6b63 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 9fa8046f50bcb88ab9183ee1f22de5adc42bf92a
+refs/heads/master: 38e2299a641d93d029eb559e096648ab75a22be2
diff --git a/trunk/fs/xfs/xfs_inode.c b/trunk/fs/xfs/xfs_inode.c
index 8d2b36879f06..88a517fad07b 100644
--- a/trunk/fs/xfs/xfs_inode.c
+++ b/trunk/fs/xfs/xfs_inode.c
@@ -1393,6 +1393,16 @@ xfs_itrunc_trace(
  * calling into the buffer/page cache code and we can't hold the
  * inode lock when we do so.
  *
+ * We need to wait for any direct I/Os in flight to complete before we
+ * proceed with the truncate. This is needed to prevent the extents
+ * being read or written by the direct I/Os from being removed while the
+ * I/O is in flight as there is no other method of synchronising
+ * direct I/O with the truncate operation.  Also, because we hold
+ * the IOLOCK in exclusive mode, we prevent new direct I/Os from being
+ * started until the truncate completes and drops the lock. Essentially,
+ * the vn_iowait() call forms an I/O barrier that provides strict ordering
+ * between direct I/Os and the truncate operation.
+ *
  * The flags parameter can have either the value XFS_ITRUNC_DEFINITE
  * or XFS_ITRUNC_MAYBE.  The XFS_ITRUNC_MAYBE value should be used
  * in the case that the caller is locking things out of order and