Re: [RFC PATCH v2 16/19] RDMA/uverbs: Add back pointer to system file object

Jason Gunthorpe
2019-08-13T18:00:22Z

On Tue, Aug 13, 2019 at 10:41:42AM -0700, Ira Weiny wrote:

> And I was pretty sure uverbs_destroy_ufile_hw() would take care of (or ensure
> that some other thread is) destroying all the MR's we have associated with this
> FD.

fd's can't be revoked, so destroy_ufile_hw() can't touch them. It
deletes any underlying HW resources, but the FD persists.

> > This is why having a back pointer like this is so ugly, it creates a
> > reference counting cycle
>
> Yep... I worked through this... and it was giving me fits...
>
> Anyway, the struct file is the only object in the core which was reasonable to
> store this information in since that is what is passed around to other
> processes...

It could be passed down in the uattr_bundle, once you are in file operations
handle the file is guarenteed to exist, and we've now arranged things
so the uattr_bundle flows into the umem, as umems can only be
established under a system call.

Jason