• Miao Xie's avatar
    Btrfs: fix orphan transaction on the freezed filesystem · 354aa0fb
    Miao Xie authored
    With the following debug patch:
    
     static int btrfs_freeze(struct super_block *sb)
     {
    + 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
    +	struct btrfs_transaction *trans;
    +
    +	spin_lock(&fs_info->trans_lock);
    +	trans = fs_info->running_transaction;
    +	if (trans) {
    +		printk("Transid %llu, use_count %d, num_writer %d\n",
    +			trans->transid, atomic_read(&trans->use_count),
    +			atomic_read(&trans->num_writers));
    +	}
    +	spin_unlock(&fs_info->trans_lock);
     	return 0;
     }
    
    I found there was a orphan transaction after the freeze operation was done.
    
    It is because the transaction may not be committed when the transaction handle
    end even though it is the last handle of the current transaction. This design
    avoid committing the transaction frequently, but also introduce the above
    problem.
    
    So I add btrfs_attach_transaction() which can catch the current transaction
    and commit it. If there is no transaction, it will return ENOENT, and do not
    anything.
    
    This function also can be used to instead of btrfs_join_transaction_freeze()
    because it don't increase the writer counter and don't start a new transaction,
    so it also can fix the deadlock between sync and freeze.
    
    Besides that, it is used to instead of btrfs_join_transaction() in
    transaction_kthread(), because if there is no transaction, the transaction
    kthread needn't anything.
    Signed-off-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
    354aa0fb
transaction.h 4.85 KB