Btrfs: separate sequence numbers for delayed ref tracking and tree mod log

Sequence numbers for delayed refs have been introduced in the first version
of the qgroup patch set. To solve the problem of find_all_roots on a busy
file system, the tree mod log was introduced. The sequence numbers for that
were simply shared between those two users.

However, at one point in qgroup's quota accounting, there's a statement
accessing the previous sequence number, that's still just doing (seq - 1)
just as it would have to in the very first version.

To satisfy that requirement, this patch makes the sequence number counter 64
bit and splits it into a major part (used for qgroup sequence number
counting) and a minor part (incremented for each tree modification in the
log). This enables us to go exactly one major step backwards, as required
for qgroups, while still incrementing the sequence counter for tree mod log
insertions to keep track of their order. Keeping them in a single variable
means there's no need to change all the code dealing with comparisons of two
sequence numbers.

The sequence number is reset to 0 on commit (not new in this patch), which
ensures we won't overflow the two 32 bit counters.

Without this fix, the qgroup tracking can occasionally go wrong and WARN_ONs
from the tree mod log code may happen.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index f175471da882..e5c56238b6c6 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1242,9 +1242,11 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
         case BTRFS_ADD_DELAYED_REF:
         case BTRFS_ADD_DELAYED_EXTENT:
                 sgn = 1;
+                seq = btrfs_tree_mod_seq_prev(node->seq);
                 break;
         case BTRFS_DROP_DELAYED_REF:
                 sgn = -1;
+                seq = node->seq;
                 break;
         case BTRFS_UPDATE_DELAYED_HEAD:
                 return 0;
@@ -1254,14 +1256,14 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
 
         /*
          * the delayed ref sequence number we pass depends on the direction of
-         * the operation. for add operations, we pass (node->seq - 1) to skip
+         * the operation. for add operations, we pass
+         * tree_mod_log_prev_seq(node->seq) to skip
          * the delayed ref's current sequence number, because we need the state
          * of the tree before the add operation. for delete operations, we pass
          * (node->seq) to include the delayed ref's current sequence number,
          * because we need the state of the tree after the delete operation.
          */
-        ret = btrfs_find_all_roots(trans, fs_info, node->bytenr,
-                                   sgn > 0 ? node->seq - 1 : node->seq, &roots);
+        ret = btrfs_find_all_roots(trans, fs_info, node->bytenr, seq, &roots);
         if (ret < 0)
                 return ret;
 
@@ -1772,8 +1774,9 @@ void assert_qgroups_uptodate(struct btrfs_trans_handle *trans)
 {
         if (list_empty(&trans->qgroup_ref_list) && !trans->delayed_ref_elem.seq)
                 return;
-        printk(KERN_ERR "btrfs: qgroups not uptodate in trans handle %p: list is%s empty, seq is %llu\n",
+        pr_err("btrfs: qgroups not uptodate in trans handle %p: list is%s empty, seq is %#x.%x\n",
                 trans, list_empty(&trans->qgroup_ref_list) ? "" : " not",
-                trans->delayed_ref_elem.seq);
+                (u32)(trans->delayed_ref_elem.seq >> 32),
+                (u32)trans->delayed_ref_elem.seq);
         BUG();
 }