Btrfs: tree mod log sanity checks in join_transaction

When a fresh transaction begins, the tree mod log must be clean. Users of
the tree modification log must ensure they never span across transaction
boundaries.

We reset the sequence to 0 in this safe situation to make absolutely sure
overflow can't happen.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index eb2bd826bb043442a4874e9321cb6291e160be72..667735fb45e6f851b0fe56e4af2ded66e77ae9b6 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -122,6 +122,24 @@ loop:
        cur_trans->delayed_refs.flushing = 0;
        cur_trans->delayed_refs.run_delayed_start = 0;
        cur_trans->delayed_refs.seq = 1;
+
+       /*
+        * although the tree mod log is per file system and not per transaction,
+        * the log must never go across transaction boundaries.
+        */
+       smp_mb();
+       if (!list_empty(&fs_info->tree_mod_seq_list)) {
+               printk(KERN_ERR "btrfs: tree_mod_seq_list not empty when "
+                       "creating a fresh transaction\n");
+               WARN_ON(1);
+       }
+       if (!RB_EMPTY_ROOT(&fs_info->tree_mod_log)) {
+               printk(KERN_ERR "btrfs: tree_mod_log rb tree not empty when "
+                       "creating a fresh transaction\n");
+               WARN_ON(1);
+       }
+       atomic_set(&fs_info->tree_mod_seq, 0);
+
        init_waitqueue_head(&cur_trans->delayed_refs.seq_wait);
        spin_lock_init(&cur_trans->commit_lock);
        spin_lock_init(&cur_trans->delayed_refs.lock);