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

[Serhat Kumral <serhatkumral1@gmail.com>]

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;
+		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