[PATCH 4/4] jbd2: use mutex_lock_io() for journal->j_checkpoint_mutex

When an ext4 fs is bogged down by a lot of metadata IOs (in the reported case, it was deletion of millions of files, but any massive amount of journal writes would do), after the journal is filled up, tasks which try to access the filesystem and aren't currently performing the journal writes end

[PATCH 4/4] jbd2: use mutex_lock_io() for journal->j_checkpoint_mutex

When an ext4 fs is bogged down by a lot of metadata IOs (in the reported case, it was deletion of millions of files, but any massive amount of journal writes would do), after the journal is filled up, tasks which try to access the filesystem and aren't currently performing the journal writes end