[PATCH 1/5] btrfs: skip tree blocks in btrfs_get_extent_owner_root()

[Siddharth Mishra <smish149@asu.edu>]

[BUG]
With simple quotas enabled on a filesystem without the skinny-metadata
feature, deleting a subvolume triggers the following warning:

 ------------[ cut here ]------------
 WARNING: fs/btrfs/extent-tree.c:393 at
   btrfs_get_extent_inline_ref_type+0x1b9/0x2d0, CPU#1: btrfs-cleaner/84
 RIP: 0010:btrfs_get_extent_inline_ref_type (fs/btrfs/extent-tree.c:393)
 Call Trace:
  <TASK>
  btrfs_get_extent_owner_root (fs/btrfs/extent-tree.c:3128)
  btrfs_lookup_extent_info (fs/btrfs/extent-tree.c:187)
  walk_down_proc (fs/btrfs/extent-tree.c:5647)
  walk_down_tree (fs/btrfs/extent-tree.c:6170)
  btrfs_drop_snapshot (fs/btrfs/extent-tree.c:6392)
  btrfs_clean_one_deleted_snapshot (fs/btrfs/transaction.c:2728)
  cleaner_kthread (fs/btrfs/disk-io.c:1553)
  kthread (kernel/kthread.c:436)
  ret_from_fork (arch/x86/kernel/process.c:158)
  ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
  </TASK>
 ---[ end trace 0000000000000000 ]---
 BTRFS error (device vda): eb 30720000 iref 0x3ee6 invalid extent
   inline ref type 0

Writing to a snapshot (update_ref_for_cow()) or a metadata balance
(relocate_block_group()) trigger the same warning.

[CAUSE]
Without skinny-metadata, the extent item of a tree block is an
EXTENT_ITEM with the TREE_BLOCK flag, and a btrfs_tree_block_info sits
between the btrfs_extent_item and the first inline ref:

	item 3 key (30441472 EXTENT_ITEM 16384) itemoff 16079 itemsize 51
		refs 1 gen 5 flags TREE_BLOCK
		tree block key (256 INODE_ITEM 0) level 0
		^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
		(176 0x5) tree block backref root FS_TREE

But btrfs_get_extent_owner_root() always takes the first inline ref
right after the btrfs_extent_item:

	ptr = (unsigned long)(ei + 1);

So for such a tree block it reads the lowest byte of the first key
objectid as the inline ref type. For the key above that byte is 0, and
btrfs_get_extent_inline_ref_type() warns. If the byte happens to be
BTRFS_EXTENT_OWNER_REF_KEY (172), the key bytes are returned as the
owner root.

The filesystem is valid. It can be reproduced with:

  mkfs.btrfs -f -O ^skinny-metadata $dev
  mount $dev $mnt
  btrfs quota enable --simple $mnt
  btrfs subvolume create $mnt/sv
  btrfs subvolume delete $mnt/sv
  btrfs subvolume sync $mnt

[FIX]
Owner refs are only added to data extents, never to tree blocks, so
return 0 for an extent item with the TREE_BLOCK flag before looking at
its inline refs. This covers both the EXTENT_ITEM and the METADATA_ITEM
layouts, and gives the same result as on a skinny-metadata filesystem,
where the first inline ref of a tree block is never an owner ref.

Fixes: 8d2990914073 ("btrfs: add helper for inline owner ref lookup")
Cc: stable@vger.kernel.org # 6.7+
Signed-off-by: Siddharth Mishra <smish149@asu.edu>
---
 fs/btrfs/extent-tree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9b0a5c6b9..3ab4f2696 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3117,6 +3117,9 @@ u64 btrfs_get_extent_owner_root(struct btrfs_fs_info *fs_info,
 		return 0;
 
 	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
+	if (btrfs_extent_flags(leaf, ei) & BTRFS_EXTENT_FLAG_TREE_BLOCK)
+		return 0;
+
 	ptr = (unsigned long)(ei + 1);
 	end = (unsigned long)ei + btrfs_item_size(leaf, slot);
 
-- 
2.54.0