Re: [PATCH rdma-next 11/23] RDMA/mlx5: Add shadow FIFO infrastructure for UMR completions

[Yishai Hadas <yishaih@nvidia.com>]

On 07/11/2026 22:24, netdev-bot+sashiko@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found more severe
> issue(s) in other patches of this series. This mail is only an FYI, in case
> you want to address the nit picks below when you respin.
> 
> Low priority / nit picks for your consideration:
> 
> - [Low] The commit message's design premise is wrong.
> 
> --
> 
> RDMA/mlx5: Add shadow FIFO infrastructure for UMR completions
> 
> This commit adds a shadow FIFO of posted UMR contexts in adversarial
> mode. A later patch can then check each UMR CQE against the oldest
> pending request instead of trusting the CQE wqe_counter. Each context
> also records the SQ producer counter it was posted at.
> 
>> The UMR QP is RC and signals every WR, so its completions arrive in
>> posting order.
> 
> [Severity: Low]
> Is this description accurate? The UMR QP does not look like an RC QP.
> 
> mlx5r_umr_resource_init() in drivers/infiniband/hw/mlx5/umr.c creates it
> as a REG_UMR QP:
> 
> drivers/infiniband/hw/mlx5/umr.c:mlx5r_umr_resource_init() {
>      ...
> 	init_attr.qp_type = MLX5_IB_QPT_REG_UMR;
>      ...
> }
> 
> to_mlx5_st() in drivers/infiniband/hw/mlx5/qp.c maps that type to its
> own service type, not MLX5_QP_ST_RC:
> 
> 	case MLX5_IB_QPT_REG_UMR:	return MLX5_QP_ST_REG_UMR;
> 
> mlx5r_umr_qp_rst2rts() also moves the QP to RTS without a remote QPN or
> a path, which an RC connection would need.
> 
> The shadow FIFO design depends on in-order completion. The consumer added
> later in the series, mlx5_ib_poll_one_umr(), treats any CQE whose
> wqe_counter differs from the FIFO head as forged.
> 
> The in-order conclusion is probably still correct, since mlx5 send queues
> complete in order and the generic poll path already relies on that when
> it sets wq->tail = wq->wqe_head[idx] + 1. Only the stated reason seems
> wrong.
> 
> Could the message say that the UMR SQ (a REG_UMR service type QP)
> completes in posting order, instead of calling the QP RC?
> 

Right, will fix the commit message in V1.

Yishai