em = lookup_extent_mapping(em_tree, chunk_start, 1);
read_unlock(&em_tree->lock);
- BUG_ON(!em || em->start != chunk_start);
+ if (!em) {
+ printk(KERN_ERR "btrfs: couldn't find em for chunk %Lu\n",
+ chunk_start);
+ return -EIO;
+ }
+
+ if (em->start != chunk_start) {
+ printk(KERN_ERR "btrfs: bad chunk start, em=%Lu, wanted=%Lu\n",
+ em->start, chunk_start);
+ free_extent_map(em);
+ return -EIO;
+ }
map = (struct map_lookup *)em->bdev;
length = em->len;