linux-kernel - [PATCH v2] net: macb: Relocate mog_init_rings() callback from macb_mac_link_up() to macb

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Message-ID: <20251209085238.2570041-1-xiaolei.wang@windriver.com>
Date: Tue,  9 Dec 2025 16:52:37 +0800
From: Xiaolei Wang <xiaolei.wang@...driver.com>
To: pabeni@...hat.com, nicolas.ferre@...rochip.com, claudiu.beznea@...on.dev,
        andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, rmk+kernel@...linux.org.uk, Kexin.Hao@...driver.com,
        xiaolei.wang@...driver.com
Cc: netdev@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] net: macb: Relocate mog_init_rings() callback from macb_mac_link_up() to macb_open()

In the non-RT kernel, local_bh_disable() merely disables preemption,
whereas it maps to an actual spin lock in the RT kernel. Consequently,
when attempting to refill RX buffers via netdev_alloc_skb() in
macb_mac_link_up(), a deadlock scenario arises as follows:
  Chain caused by macb_mac_link_up():
   &bp->lock --> (softirq_ctrl.lock)

   Chain caused by macb_start_xmit():
   (softirq_ctrl.lock) --> _xmit_ETHER#2 --> &bp->lock

Notably, invoking the mog_init_rings() callback upon link establishment
is unnecessary. Instead, we can exclusively call mog_init_rings() within
the ndo_open() callback. This adjustment resolves the deadlock issue.
Given that mog_init_rings() is only applicable to
non-MACB_CAPS_MACB_IS_EMAC cases, we can simply move it to macb_open()
and simultaneously eliminate the MACB_CAPS_MACB_IS_EMAC check.

Fixes: 633e98a711ac ("net: macb: use resolved link config in mac_link_up()")
Cc: stable@...r.kernel.org
Suggested-by: Kevin Hao <kexin.hao@...driver.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@...driver.com>
---

V1: https://patchwork.kernel.org/project/netdevbpf/patch/20251128103647.351259-1-xiaolei.wang@windriver.com/
V2: Update the correct lock dependency chain and add the Fix tag.

 drivers/net/ethernet/cadence/macb_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index ca2386b83473..064fccdcf699 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -744,7 +744,6 @@ static void macb_mac_link_up(struct phylink_config *config,
 		/* Initialize rings & buffers as clearing MACB_BIT(TE) in link down
 		 * cleared the pipeline and control registers.
 		 */
-		bp->macbgem_ops.mog_init_rings(bp);
 		macb_init_buffers(bp);

 		for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue)
@@ -2991,6 +2990,8 @@ static int macb_open(struct net_device *dev)
 		goto pm_exit;
 	}

+	bp->macbgem_ops.mog_init_rings(bp);
+
 	for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
 		napi_enable(&queue->napi_rx);
 		napi_enable(&queue->napi_tx);
-- 
2.43.0