Btrfs: fix an oops when we fail to relocate tree blocks

During balance test, we hit an oops:
[ 2013.841551] kernel BUG at fs/btrfs/relocation.c:1174!

The problem is that if we fail to relocate tree blocks, we should
update backref cache, otherwise, some pending nodes are not updated
while snapshot check @cache->last_trans is within one transaction
and won't update it and then oops happen.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 9189f9e..07b3b36 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4009,6 +4009,12 @@ restart:
                if (!RB_EMPTY_ROOT(&blocks)) {
                        ret = relocate_tree_blocks(trans, rc, &blocks);
                        if (ret < 0) {
+                               /*
+                                * if we fail to relocate tree blocks, force to update
+                                * backref cache when committing transaction.
+                                */
+                               rc->backref_cache.last_trans = trans->transid - 1;
+
                                if (ret != -EAGAIN) {
                                        err = ret;
                                        break;