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Description of problem:

VDO has a journal. This journal is reaped to regain space. In order to record the new start of the journal after reaping, the journal must issue a flush to insure all metadata depending on the reaped journal entries is stably committed in disk.

In the case where we switch sync->async, the journal doesn't make a object with which to flush when it is created in sync mode, and then since it does not have an object with which to flush doesn't do the flush when reaping when it is in async mode. 

This can result in loss of metadata consistency or data loss under certain very rare (never observed) circumstances.



Version-Release number of selected component (if applicable):
6.1.0.123

How reproducible:
Theoretical.

Steps to Reproduce:
0. Switch sync->async write policy.
1. Get exceedingly lucky in crashing at just the right time on a disk which drops writes out of order on crash. One needs the new recovery journal start written and committed to disk, but some metadata depending on the reaped journal blocks, written earlier, not committed to disk.
3.

Actual results:
Observe metadata inconsistency or data loss.

Expected results:
No such problem

Additional info: