MFC r275922: MFV r275914:

As of r270383, the dbuf_compare comparator compares the dbuf
attributes in the following order:

      db_level (indirect level)
      db_blkid (block number)
      db_state (current state)
      the address of the element

Because db_state is being considered before the element's state,
changing of db_state would affect balancedness of the AVL tree,
even when the address of element compares differently.  For
instance, in dbuf_create, db_state may be altered after the
node is inserted into the AVL tree and may break AVL tree
balancedness.

Instead of using db_state as a comparision critera (introduced
in r270383), consider it only when we are doing a lookup, that
is one of the two dbuf pointers contains DB_SEARCH.

Illumos issue:
    5422 preserve AVL invariants in dn_dbufs

1 files changed, 4 insertions, 6 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
index 66552c3..665165a 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
@@ -81,16 +81,14 @@ dbuf_compare(const void *x1, const void *x2)
 		return (1);
 	}
 
-	if (d1->db_state < d2->db_state) {
+	if (d1->db_state == DB_SEARCH) {
+		ASSERT3S(d2->db_state, !=, DB_SEARCH);
 		return (-1);
-	}
-	if (d1->db_state > d2->db_state) {
+	} else if (d2->db_state == DB_SEARCH) {
+		ASSERT3S(d1->db_state, !=, DB_SEARCH);
 		return (1);
 	}
 
-	ASSERT3S(d1->db_state, !=, DB_SEARCH);
-	ASSERT3S(d2->db_state, !=, DB_SEARCH);
-
 	if ((uintptr_t)d1 < (uintptr_t)d2) {
 		return (-1);
 	}