btrfs: qgroup: convert PREALLOC to PERTRANS after record_root_in_trans

commit 211de93367304ab395357f8cb12568a4d1e20701 upstream.

The transaction is only able to free PERTRANS reservations for a root
once that root has been recorded with the TRANS tag on the roots radix
tree. Therefore, until we are sure that this root will get tagged, it
isn't safe to convert. Generally, this is not an issue as *some*
transaction will likely tag the root before long and this reservation
will get freed in that transaction, but technically it could stick
around until unmount and result in a warning about leaked metadata
reservation space.

This path is most exercised by running the generic/269 fstest with
CONFIG_BTRFS_DEBUG.

Fixes: a6496849671a ("btrfs: fix start transaction qgroup rsv double free")
CC: stable@vger.kernel.org # 6.6+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index bf8e64c766b63b4c8b424f4437791eaea12f24a2..f1705ae59e4a90e1f2af0aa148f50565c2bd333d 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -747,14 +747,6 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
                h->reloc_reserved = reloc_reserved;
        }
 
-       /*
-        * Now that we have found a transaction to be a part of, convert the
-        * qgroup reservation from prealloc to pertrans. A different transaction
-        * can't race in and free our pertrans out from under us.
-        */
-       if (qgroup_reserved)
-               btrfs_qgroup_convert_reserved_meta(root, qgroup_reserved);
-
 got_it:
        if (!current->journal_info)
                current->journal_info = h;
@@ -788,8 +780,15 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
                 * not just freed.
                 */
                btrfs_end_transaction(h);
-               return ERR_PTR(ret);
+               goto reserve_fail;
        }
+       /*
+        * Now that we have found a transaction to be a part of, convert the
+        * qgroup reservation from prealloc to pertrans. A different transaction
+        * can't race in and free our pertrans out from under us.
+        */
+       if (qgroup_reserved)
+               btrfs_qgroup_convert_reserved_meta(root, qgroup_reserved);
 
        return h;