Re: [PATCH] ublk: restore auto buf unregister refcount optimization

[Ming Lei <ming.lei@redhat.com>]

On Wed, Jan 28, 2026 at 01:56:34PM -0700, Caleb Sander Mateos wrote:
> Commit 1ceeedb59749 ("ublk: optimize UBLK_IO_UNREGISTER_IO_BUF on daemon
> task") optimized ublk request buffer unregistration to use a non-atomic
> reference count decrement when performed on the ublk_io's daemon task.
> The optimization applied to auto buffer unregistration, which happens as
> part of handling UBLK_IO_COMMIT_AND_FETCH_REQ on the daemon task.
> However, commit b749965edda8 ("ublk: remove ublk_commit_and_fetch()")
> reordered the ublk_sub_req_ref() for the completed request before the
> io_buffer_unregister_bvec() call. As a result, task_registered_buffers
> is already 0 when io_buffer_unregister_bvec() calls ublk_io_release()
> and the non-atomic refcount optimization doesn't apply.
> Move the io_buffer_unregister_bvec() call back to before
> ublk_need_complete_req() to restore the reference counting optimization.
> 
> Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
> Fixes: b749965edda8 ("ublk: remove ublk_commit_and_fetch()")

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming