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

[Gang He]

Hi David,

On 2021/8/13 1:45, David Teigland wrote:
> 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.
These dlm_lock and dlm_unlock are invoked in the same node, or the 
different nodes?

> 
> 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.
If I retry dlm_lock() repeatedly, I just wonder if this will lead to 
kernel soft lockup or waste lots of CPU.
If dlm_lock() function returns -EAGAIN, how should we handle this case?
retry it repeatedly?

Thanks
Gang

> 
> Dave
>