[Cluster-devel] Why does dlm_lock function fails when downconvert a dlm lock?

[David Teigland]

On Thu, Aug 12, 2021 at 01:44:53PM +0800, Gang He wrote:
> In fact, I can reproduce this problem stably.
> I want to know if this error happen is by our expectation? since there is
> not any extreme pressure test.
> Second, how should we handle these error cases? call dlm_lock function
> again? maybe the function will fails again, that will lead to kernel
> soft-lockup after multiple re-tries.

What's probably happening is that ocfs2 calls dlm_unlock(CANCEL) to cancel
an in-progress dlm_lock() request.  Before the cancel completes (or the
original request completes), ocfs2 calls dlm_lock() again on the same
resource.  This dlm_lock() returns -EBUSY because the previous request has
not completed, either normally or by cancellation.  This is expected.

A couple options to try: wait for the original request to complete
(normally or by cancellation) before calling dlm_lock() again, or retry
dlm_lock() on -EBUSY.

Dave