btrfs: do not BUG_ON() when freeing tree block after error

When freeing a tree block, at btrfs_free_tree_block(), if we fail to
create a delayed reference we don't deal with the error and just do a
BUG_ON(). The error most likely to happen is -ENOMEM, and we have a
comment mentioning that only -ENOMEM can happen, but that is not true,
because in case qgroups are enabled any error returned from
btrfs_qgroup_trace_extent_post() (can be -EUCLEAN or anything returned
from btrfs_search_slot() for example) can be propagated back to
btrfs_free_tree_block().

So stop doing a BUG_ON() and return the error to the callers and make
them abort the transaction to prevent leaking space. Syzbot was
triggering this, likely due to memory allocation failure injection.

Reported-by: syzbot+a306f914b4d01b3958fe@syzkaller.appspotmail.com
Link: https://lore.kernel.org/linux-btrfs/000000000000fcba1e05e998263c@google.com/
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 14 insertions, 10 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index eda424192164..58a72a57414a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3419,10 +3419,10 @@ out_delayed_unlock:
 	return 0;
 }
 
-void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
-			   u64 root_id,
-			   struct extent_buffer *buf,
-			   u64 parent, int last_ref)
+int btrfs_free_tree_block(struct btrfs_trans_handle *trans,
+			  u64 root_id,
+			  struct extent_buffer *buf,
+			  u64 parent, int last_ref)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_block_group *bg;
@@ -3449,11 +3449,12 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
 		btrfs_init_tree_ref(&generic_ref, btrfs_header_level(buf), 0, false);
 		btrfs_ref_tree_mod(fs_info, &generic_ref);
 		ret = btrfs_add_delayed_tree_ref(trans, &generic_ref, NULL);
-		BUG_ON(ret); /* -ENOMEM */
+		if (ret < 0)
+			return ret;
 	}
 
 	if (!last_ref)
-		return;
+		return 0;
 
 	if (btrfs_header_generation(buf) != trans->transid)
 		goto out;
@@ -3510,6 +3511,7 @@ out:
 	 * matter anymore.
 	 */
 	clear_bit(EXTENT_BUFFER_CORRUPT, &buf->bflags);
+	return 0;
 }
 
 /* Can return -ENOMEM */
@@ -5754,7 +5756,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 				 struct walk_control *wc)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
-	int ret;
+	int ret = 0;
 	int level = wc->level;
 	struct extent_buffer *eb = path->nodes[level];
 	u64 parent = 0;
@@ -5849,12 +5851,14 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 			goto owner_mismatch;
 	}
 
-	btrfs_free_tree_block(trans, btrfs_root_id(root), eb, parent,
-			      wc->refs[level] == 1);
+	ret = btrfs_free_tree_block(trans, btrfs_root_id(root), eb, parent,
+				    wc->refs[level] == 1);
+	if (ret < 0)
+		btrfs_abort_transaction(trans, ret);
 out:
 	wc->refs[level] = 0;
 	wc->flags[level] = 0;
-	return 0;
+	return ret;
 
 owner_mismatch:
 	btrfs_err_rl(fs_info, "unexpected tree owner, have %llu expect %llu",