Re: [PATCH rdma-next v1] RDMA/uverbs: Propagate errors from rdma_lookup_get_uobject()

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Feb 26, 2025 at 03:54:13PM +0200, Leon Romanovsky wrote:
> From: Maher Sanalla <msanalla@nvidia.com>
> 
> Currently, the IB uverbs API calls uobj_get_uobj_read(), which in turn
> uses the rdma_lookup_get_uobject() helper to retrieve user objects.
> In case of failure, uobj_get_uobj_read() returns NULL, overriding the
> error code from rdma_lookup_get_uobject(). The IB uverbs API then
> translates this NULL to -EINVAL, masking the actual error and
> complicating debugging. For example, applications calling ibv_modify_qp
> that fails with EBUSY when retrieving the QP uobject will see the
> overridden error code EINVAL instead, masking the actual error.

I still didn't see an answer to the question of why userspace would
hit an EBUSY down that path in a way we need to care about? That is
doing dumb racing thread stuff that nothing should be doing..

> Furthermore, based on rdma-core commit:
> "2a22f1ced5f3 ("Merge pull request #1568 from jakemoroni/master")"
> Kernel's IB uverbs return values are either ignored and passed on as is
> to application or overridden with other errnos in a few cases.

I don't understand this sentence

Is this the defence of why it is safe to do this? But if the rdma-core
overrides them what is the point of forwarding?

Jason