netdev - [PATCH v2 2/2] net: io_uring/zcrx: call netdev_queue_get_dma

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Message-ID: <20251029231654.1156874-3-dw@davidwei.uk>
Date: Wed, 29 Oct 2025 16:16:54 -0700
From: David Wei <dw@...idwei.uk>
To: io-uring@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>,
	Pavel Begunkov <asml.silence@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>
Subject: [PATCH v2 2/2] net: io_uring/zcrx: call netdev_queue_get_dma_dev() under instance lock

netdev ops must be called under instance lock or rtnl_lock, but
io_register_zcrx_ifq() isn't doing this for netdev_queue_get_dma_dev().
Fix this by taking the instance lock using netdev_get_by_index_lock().

Extended the instance lock section to include attaching a memory
provider. Could not move io_zcrx_create_area() outside, since the dmabuf
codepath IORING_ZCRX_AREA_DMABUF requires ifq->dev.

Fixes: 59b8b32ac8d4 ("io_uring/zcrx: add support for custom DMA devices")
Signed-off-by: David Wei <dw@...idwei.uk>
---
 io_uring/zcrx.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index a816f5902091..5599883f8941 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -599,27 +599,28 @@ int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 	if (ret)
 		goto err;
 
-	ifq->netdev = netdev_get_by_index(current->nsproxy->net_ns, reg.if_idx,
-					  &ifq->netdev_tracker, GFP_KERNEL);
+	ifq->netdev = netdev_get_by_index_lock(current->nsproxy->net_ns, reg.if_idx);
 	if (!ifq->netdev) {
 		ret = -ENODEV;
-		goto err;
+		goto netdev_unlock;
 	}
 
 	ifq->dev = netdev_queue_get_dma_dev(ifq->netdev, reg.if_rxq);
 	if (!ifq->dev) {
 		ret = -EOPNOTSUPP;
-		goto err;
+		goto netdev_unlock;
 	}
+	netdev_hold(ifq->netdev, &ifq->netdev_tracker, GFP_KERNEL);
 	get_device(ifq->dev);
 
 	ret = io_zcrx_create_area(ifq, &area);
 	if (ret)
-		goto err;
+		goto netdev_unlock;
 
 	mp_param.mp_ops = &io_uring_pp_zc_ops;
 	mp_param.mp_priv = ifq;
-	ret = net_mp_open_rxq(ifq->netdev, reg.if_rxq, &mp_param);
+	ret = __net_mp_open_rxq(ifq->netdev, reg.if_rxq, &mp_param, NULL);
+	netdev_unlock(ifq->netdev);
 	if (ret)
 		goto err;
 	ifq->if_rxq = reg.if_rxq;
@@ -640,6 +641,8 @@ int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 		goto err;
 	}
 	return 0;
+netdev_unlock:
+	netdev_unlock(ifq->netdev);
 err:
 	scoped_guard(mutex, &ctx->mmap_lock)
 		xa_erase(&ctx->zcrx_ctxs, id);
-- 
2.47.3