Re: [PATCH v2] RDMA/srpt: Clamp the CQ size request to max_cqe

[Leon Romanovsky <leon@kernel.org>]

On Fri, Sep 04, 2026 at 11:02:40PM +0300, Serhat Kumral wrote:
> srpt_create_ch_ib() asks ib_cq_pool_get() for ch->rq_size + sq_size
> completion queue entries. rq_size is bounded by max_qp_wr, but sq_size
> comes from the per-port srp_sq_size configfs attribute, which is only
> validated against MAX_SRPT_SRQ_SIZE (65535) and never compared with
> dev->attrs.max_cqe. The largest configuration srpt accepts therefore
> asks for 128 + 65535 = 65663 entries, while rxe caps max_cqe at 32767
> and cxgb4 and ionic are in the same range.
> 
> Such a request cannot be met, and ib_cq_pool_get() does not reject it.
> It clamps every CQ it creates to max_cqe, so no CQ it adds to the pool
> can ever fit the request, and it keeps allocating batches until the
> allocation fails. A single SRP login against such a target exhausts
> memory:
> 
>   Out of memory and no killable processes...
>   Kernel panic - not syncing: System is deadlocked on memory
>   Workqueue: ib_cm cm_work_handler
>   Call Trace:
>    __vmalloc_node_range_noprof
>    vmalloc_user_noprof
>    rxe_queue_init
>    rxe_cq_from_init
>    rxe_create_cq
>    __ib_alloc_cq
>    ib_cq_pool_get
>    srpt_cm_req_recv.cold
> 
> Before commit c804af2c1d31 ("IB/srpt: use new shared CQ mechanism") the
> same request went to ib_alloc_cq_any(), which rejected it with -EINVAL.
> 
> The existing backoff, which halves sq_size when queue pair creation
> fails, only runs after ib_cq_pool_get() has returned, so shrink sq_size
> before asking for the CQ. rq_size never exceeds MAX_SRPT_RQ_SIZE (128),
> far below the max_cqe any device reports in practice, so the
> subtraction does not underflow. With the clamp the same login proceeds
> exactly like a correctly sized target.
> 
> Fixes: c804af2c1d31 ("IB/srpt: use new shared CQ mechanism")
> Signed-off-by: Serhat Kumral <serhatkumral1@gmail.com>
> ---
> Changes since v1:
> - Move the fix from the RDMA core to ib_srpt, as requested by Leon
>   Romanovsky.
> - Clamp sq_size before the CQ request instead of rejecting oversized
>   requests in ib_cq_pool_get().
> 
> v1: https://lore.kernel.org/linux-rdma/20260831171354.72140-1-serhatkumral1@gmail.com/
> 
>  drivers/infiniband/ulp/srpt/ib_srpt.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/infiniband/ulp/srpt/ib_srpt.c b/drivers/infiniband/ulp/srpt/ib_srpt.c
> index 7197d95f2216..58064a4c606b 100644
> --- a/drivers/infiniband/ulp/srpt/ib_srpt.c
> +++ b/drivers/infiniband/ulp/srpt/ib_srpt.c
> @@ -1867,6 +1867,13 @@ static int srpt_create_ch_ib(struct srpt_rdma_ch *ch)
>  	if (!qp_init)
>  		goto out;
>  
> +	/* The send and receive queues share a single CQ. */
> +	if (ch->rq_size + sq_size > attrs->max_cqe) {
> +		sq_size = attrs->max_cqe - ch->rq_size;

I don't think that Sashiko concern is real
https://sashiko.dev/#/patchset/20260904200240.48976-1-serhatkumral1@gmail.com
but it is worth to write it in a way to avoid triggering this warning.

For example
/* Catch drivers that incorrectly set ch->rq_size */
WARN_ON_ONCE(attrs->max_cqe < ch->rq_size)

Thanks

> +		pr_debug("reduced sq_size to %u because max_cqe is %u\n",
> +			 sq_size, attrs->max_cqe);
> +	}
> +
>  retry:
>  	ch->cq = ib_cq_pool_get(sdev->device, ch->rq_size + sq_size, -1,
>  				 IB_POLL_WORKQUEUE);
> 
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> -- 
> 2.53.0
>