Merge tag 'kvm-s390-master-4.16-3' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-2.6-microblaze.git] / fs / btrfs / backref.c

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index e4054e5..f94b2d8 100644 (file)
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1264,7 +1264,16 @@ again:
        while (node) {
                ref = rb_entry(node, struct prelim_ref, rbnode);
                node = rb_next(&ref->rbnode);
-               WARN_ON(ref->count < 0);
+               /*
+                * ref->count < 0 can happen here if there are delayed
+                * refs with a node->action of BTRFS_DROP_DELAYED_REF.
+                * prelim_ref_insert() relies on this when merging
+                * identical refs to keep the overall count correct.
+                * prelim_ref_insert() will merge only those refs
+                * which compare identically.  Any refs having
+                * e.g. different offsets would not be merged,
+                * and would retain their original ref->count < 0.
+                */
                if (roots && ref->count && ref->root_id && ref->parent == 0) {
                        if (sc && sc->root_objectid &&
                            ref->root_id != sc->root_objectid) {