[PATCH v2] RDMA/siw: publish QP after initialization

[Ruoyu Wang <ruoyuw560@gmail.com>]

siw_create_qp() currently calls siw_qp_add() before the queues, CQ
pointers, state, completion, and device list entry are ready. A QPN
lookup can therefore reach a QP that is still being constructed.

Move the siw_qp_add() publication step to the end of siw_create_qp(),
after the kernel-visible QP state is initialized. The QPN must still be
known before copying the siw-specific create response to userspace, so
reserve the QPN first with an empty XArray entry. This lets
siw_create_qp() report the QPN while QPN lookups still return NULL until
the QP is published.

Fixes: f29dd55b0236 ("rdma/siw: queue pair methods")
Suggested-by: Bernard Metzler <bernard.metzler@linux.dev>
Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
---
Changes in v2:
- Move the siw_qp_add() publication step to the end of siw_create_qp().
- Add siw_qp_reserve_qpn() so the udata response can still report qp_num
  before the QP becomes visible to QPN lookups.

 drivers/infiniband/sw/siw/siw.h       |  1 +
 drivers/infiniband/sw/siw/siw_qp.c    | 26 ++++++++++++++++++--------
 drivers/infiniband/sw/siw/siw_verbs.c | 14 ++++++++++++--
 3 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/drivers/infiniband/sw/siw/siw.h b/drivers/infiniband/sw/siw/siw.h
index f5fd71717b80..f8d28dd7dd86 100644
--- a/drivers/infiniband/sw/siw/siw.h
+++ b/drivers/infiniband/sw/siw/siw.h
@@ -510,6 +510,7 @@ void siw_send_terminate(struct siw_qp *qp);
 
 void siw_qp_get_ref(struct ib_qp *qp);
 void siw_qp_put_ref(struct ib_qp *qp);
+int siw_qp_reserve_qpn(struct siw_device *sdev, struct siw_qp *qp);
 int siw_qp_add(struct siw_device *sdev, struct siw_qp *qp);
 void siw_free_qp(struct kref *ref);
 
diff --git a/drivers/infiniband/sw/siw/siw_qp.c b/drivers/infiniband/sw/siw/siw_qp.c
index bb780e3904a2..7d6224ebfe71 100644
--- a/drivers/infiniband/sw/siw/siw_qp.c
+++ b/drivers/infiniband/sw/siw/siw_qp.c
@@ -1279,17 +1279,27 @@ void siw_rq_flush(struct siw_qp *qp)
 	}
 }
 
+int siw_qp_reserve_qpn(struct siw_device *sdev, struct siw_qp *qp)
+{
+	qp->sdev = sdev;
+
+	return xa_alloc(&sdev->qp_xa, &qp->base_qp.qp_num, NULL,
+			xa_limit_32b, GFP_KERNEL);
+}
+
 int siw_qp_add(struct siw_device *sdev, struct siw_qp *qp)
 {
-	int rv = xa_alloc(&sdev->qp_xa, &qp->base_qp.qp_num, qp, xa_limit_32b,
-			  GFP_KERNEL);
+	void *old;
 
-	if (!rv) {
-		kref_init(&qp->ref);
-		qp->sdev = sdev;
-		siw_dbg_qp(qp, "new QP\n");
-	}
-	return rv;
+	kref_init(&qp->ref);
+
+	old = xa_store(&sdev->qp_xa, qp_id(qp), qp, GFP_KERNEL);
+	if (xa_is_err(old))
+		return xa_err(old);
+
+	siw_dbg_qp(qp, "new QP\n");
+
+	return 0;
 }
 
 void siw_free_qp(struct kref *ref)
diff --git a/drivers/infiniband/sw/siw/siw_verbs.c b/drivers/infiniband/sw/siw/siw_verbs.c
index 1e1d262a4ae2..ef9fa9c5bf88 100644
--- a/drivers/infiniband/sw/siw/siw_verbs.c
+++ b/drivers/infiniband/sw/siw/siw_verbs.c
@@ -369,7 +369,7 @@ int siw_create_qp(struct ib_qp *ibqp, struct ib_qp_init_attr *attrs,
 	spin_lock_init(&qp->rq_lock);
 	spin_lock_init(&qp->orq_lock);
 
-	rv = siw_qp_add(sdev, qp);
+	rv = siw_qp_reserve_qpn(sdev, qp);
 	if (rv)
 		goto err_atomic;
 
@@ -482,14 +482,24 @@ int siw_create_qp(struct ib_qp *ibqp, struct ib_qp_init_attr *attrs,
 		goto err_out_xa;
 	}
 	INIT_LIST_HEAD(&qp->devq);
+	init_completion(&qp->qp_free);
+
 	spin_lock_irqsave(&sdev->lock, flags);
 	list_add_tail(&qp->devq, &sdev->qp_list);
 	spin_unlock_irqrestore(&sdev->lock, flags);
 
-	init_completion(&qp->qp_free);
+	rv = siw_qp_add(sdev, qp);
+	if (rv)
+		goto err_out_list;
 
 	return 0;
 
+err_out_list:
+	spin_lock_irqsave(&sdev->lock, flags);
+	list_del(&qp->devq);
+	spin_unlock_irqrestore(&sdev->lock, flags);
+
+	siw_put_tx_cpu(qp->tx_cpu);
 err_out_xa:
 	xa_erase(&sdev->qp_xa, qp_id(qp));
 	if (uctx) {