On Sat 24-10-15 17:14:15, Eunji Lee wrote: > This patch is to fix a (seemingly) bug of asynchronous commit process > (pinging w/ a patch). > > In asynchronous commit, JBD2 issues a "FLUSH" request only once after > issuing a commit record if a file system and a journal reside on the same > device. This can reduce redundant storage flushes relying on the checksum. > > However, it seems to incur an undesirable result in ordered mode. > Specifically, the system can crash after metadata blocks and a commit record > are successfully written to the journal (i.e., with no checksum error), but > before data blocks are reflected to the file system. Then, on the system > recovery, metadata updates in a journal area will be replayed as the > checksum has no error, even though the associated data blocks are not > reflected to the file system. This fails to provide the correct ordering - > associated data blocks are written before metadata updates are written. > > This patch flushes a storage device before issuing a commit record, even if > a journal and a file system use a same device, thereby guaranteeing the > correct ordering between metadata and data block updates. > > Without 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. Thanks for your report and detailed analysis. However this bug is already fixed - parse_options() in fs/ext4/super.c already makes sure that journal_async_commit cannot be enabled in data=ordered mode. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- 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
