[dm-devel] dm-cache coherence issue

[Joe Thornber]

On Mon, Jun 26, 2017 at 12:33:42PM +0100, Joe Thornber wrote:
> On Sat, Jun 24, 2017 at 03:56:54PM +0200, Johannes Bauer wrote:
> > So I seem to have a very basic misunderstanding of what the cleaner
> > policy/dirty pages mean. Is there a way to force the cache to flush
> > entirely? Apparently, "dmsetup wait" and/or "sync" don't do the job.
> 
> I'll try and reproduce your scenario and get back to you.

Here's a similar scenario that I've added to the dm test suite:

https://github.com/jthornber/device-mapper-test-suite/commit/457e889b0c4d510609c0d7464af07f2ebee20768

It goes through all the steps you need to use to decommission a cache
with dirty blocks.  Namely:

- switch to writethrough mode (so new io can't create new dirty blocks)
- switch to the cleaner policy
- wait for clean
- remove the cache device before accessing the origin directly

I've run it with a recent kernel, and one from about a year ago and it
passes fine.

- Joe