[Cluster-devel] [GFS2 PATCH 2/2] GFS2: Take advantage of new EXSH glock mode for rgrps

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
> Hi,
> 
> 
> On 18/04/18 17:58, Bob Peterson wrote:
> > This patch switches rgrp locking to EXSH mode so that it's only
> > taken when the rgrp is added to an active transaction, or when
> > blocks are being reserved. As soon as the transaction is ended,
> > the rgrp exclusivity is released. This allows for rgrp sharing.
> Adding the rwsem looks like a good plan. I'm not sure that I understand
> why you need to lock the rgrp exclusively for the whole transaction and
> have added the new list. Do we really need to save the pid, or is that
> just there for debugging?
> 
> Steve.

Hi,

The reason I chose to do it this way is because I wanted to guarantee
any process twiddling any bit in the bitmap or any rgrp value would
have the lock exclusively. Before anyone can twiddle a bit, they need
to add the data to the transaction. Simple way to guarantee it.

I could add the appropriate locking before every place it needs
to twiddle the bits, but the patch will look a lot bigger.
I thought the transaction is a convenient and centrally-located
place for the locking, rather than scattering them about where
future maintainers could introduce deadlocks and such.

Regards,

Bob Peterson
Red Hat File Systems