ext4: forbid journal_async_commit in data=ordered mode
Option journal_async_commit breaks gurantees of data=ordered mode as it sends only a single cache flush after writing a transaction commit block. Thus even though the transaction including the commit block is fully stored on persistent storage, file data may still linger in drives caches and will be lost on power failure. Since all checksums match on journal recovery, we replay the transaction thus possibly exposing stale user data. To fix this data exposure issue, remove the possibility to use journal_async_commit in data=ordered mode. Signed-off-by: NJan Kara <jack@suse.cz> Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
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