Hi, I am Eunji, and have a question on some parts of codes in EXT4/JBD2. (it seems to work incorrectly, though I can be wrong). During the commit, JBD2 writes "data blocks" to the file system device and writes "metadata blocks" and "commit record" to the journal device, when running in an ordered mode. The current version of code (kernel 4.1) issues a "flush" once after issuing a commit record if the file system device and the journal device are same in asynchronous commit. It is to avoid redundant flushes. However, it seems to incur an undesirable result upon a system crash, which is the metadata blocks and commit record are written to the journal device successfully, but the data blocks are not reflected to the file system location. For example, let us assume that the writes are issued in the following order. data, metadata, commit-record, and then flush Then, the system crashes after writing metadata and commit-record to the journal device, but before flushing data to the file system location (i.e., in the middle of flushing storage cache). Since the metadata block and the commit-record are both written to the journal, there is no error in checksum, and thus it would be replayed in the recovery. However, data blocks, that should be written to the file system device before the associated metadata blocks are committed to the journal, are not reflected to the media. In not using asynchronous commit, it does not matter because the commit record with WRITE_FUA guarantees to flush storage cache before the commit record is written to the journal. In summary, I think code should be modified as follows. jbd2_journal_commit_transaction (current) if (commit_transaction->t_need_data_flush && (journal->j_fs_dev != journal->j_dev) && (journal->j_flags & JBD2_BARRIER)) blkdev_issue_flush(journal->j_fs_dev, GFP_NOFS, NULL); (after modification) if (commit_transaction->t_need_data_flush && (journal->j_flags & JBD2_BARRIER)) blkdev_issue_flush(journal->j_fs_dev, GFP_NOFS, NULL); Any comments will be very appreciated. Thanks, Eunji -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
