btrfs: don't BUG_ON() when 0 reference count at btrfs_lookup_extent_info()

commit 28cb13f29faf6290597b24b728dc3100c019356f upstream.

Instead of doing a BUG_ON() handle the error by returning -EUCLEAN,
aborting the transaction and logging an error message.

Reviewed-by: Qu Wenruo <[email protected]>
Signed-off-by: Filipe Manana <[email protected]>
Signed-off-by: David Sterba <[email protected]>
[Minor conflict resolved due to code context change.]
Signed-off-by: Jianqi Ren <[email protected]>
Signed-off-by: He Zhe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: fdmanana

fs/btrfs/extent-tree.c

@@ -179,6 +179,14 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 			ei = btrfs_item_ptr(leaf, path->slots[0],
 					    struct btrfs_extent_item);
 			num_refs = btrfs_extent_refs(leaf, ei);
+			if (unlikely(num_refs == 0)) {
+				ret = -EUCLEAN;
+				btrfs_err(fs_info,
+			"unexpected zero reference count for extent item (%llu %u %llu)",
+					  key.objectid, key.type, key.offset);
+				btrfs_abort_transaction(trans, ret);
+				goto out_free;
+			}
 			extent_flags = btrfs_extent_flags(leaf, ei);
 		} else {
 			ret = -EINVAL;
@@ -190,8 +198,6 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 
 			goto out_free;
 		}
-
-		BUG_ON(num_refs == 0);
 	} else {
 		num_refs = 0;
 		extent_flags = 0;
@@ -221,10 +227,19 @@ int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
 			goto search_again;
 		}
 		spin_lock(&head->lock);
-		if (head->extent_op && head->extent_op->update_flags)
+		if (head->extent_op && head->extent_op->update_flags) {
 			extent_flags |= head->extent_op->flags_to_set;
-		else
-			BUG_ON(num_refs == 0);
+		} else if (unlikely(num_refs == 0)) {
+			spin_unlock(&head->lock);
+			mutex_unlock(&head->mutex);
+			spin_unlock(&delayed_refs->lock);
+			ret = -EUCLEAN;
+			btrfs_err(fs_info,
+			  "unexpected zero reference count for extent %llu (%s)",
+				  bytenr, metadata ? "metadata" : "data");
+			btrfs_abort_transaction(trans, ret);
+			goto out_free;
+		}
 
 		num_refs += head->ref_mod;
 		spin_unlock(&head->lock);