[PATCH net 2/2] net: macb: Protect access to net_device::in_ptr with RCU lock

[Kevin Hao <haokexin@gmail.com>]

Access to net_device::in_ptr and its members should be protected by RCU
lock. This resolves the following RCU check warning:
  WARNING: suspicious RCU usage
  7.0.0-rc3-next-20260310-yocto-standard+ #122 Not tainted
  -----------------------------
  drivers/net/ethernet/cadence/macb_main.c:5944 suspicious rcu_dereference_check() usage!

  other info that might help us debug this:

  rcu_scheduler_active = 2, debug_locks = 1
  5 locks held by rtcwake/518:
   #0: ffff000803ab1408 (sb_writers#5){.+.+}-{0:0}, at: vfs_write+0xf8/0x368
   #1: ffff0008090bf088 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0xbc/0x1c8
   #2: ffff00080098d588 (kn->active#70){.+.+}-{0:0}, at: kernfs_fop_write_iter+0xcc/0x1c8
   #3: ffff800081c84888 (system_transition_mutex){+.+.}-{4:4}, at: pm_suspend+0x1ec/0x290
   #4: ffff0008009ba0f8 (&dev->mutex){....}-{4:4}, at: device_suspend+0x118/0x4f0

  stack backtrace:
  CPU: 3 UID: 0 PID: 518 Comm: rtcwake Not tainted 7.0.0-rc3-next-20260310-yocto-standard+ #122 PREEMPT
  Hardware name: ZynqMP ZCU102 Rev1.1 (DT)
  Call trace:
   show_stack+0x24/0x38 (C)
   __dump_stack+0x28/0x38
   dump_stack_lvl+0x64/0x88
   dump_stack+0x18/0x24
   lockdep_rcu_suspicious+0x134/0x1d8
   macb_suspend+0xd8/0x4c0
   device_suspend+0x218/0x4f0
   dpm_suspend+0x244/0x3a0
   dpm_suspend_start+0x50/0x78
   suspend_devices_and_enter+0xec/0x560
   pm_suspend+0x194/0x290
   state_store+0x110/0x158
   kobj_attr_store+0x1c/0x30
   sysfs_kf_write+0xa8/0xd0
   kernfs_fop_write_iter+0x11c/0x1c8
   vfs_write+0x248/0x368
   ksys_write+0x7c/0xf8
   __arm64_sys_write+0x28/0x40
   invoke_syscall+0x4c/0xe8
   el0_svc_common+0x98/0xf0
   do_el0_svc+0x28/0x40
   el0_svc+0x54/0x1e0
   el0t_64_sync_handler+0x84/0x130
   el0t_64_sync+0x198/0x1a0

Fixes: 0cb8de39a776 ("net: macb: Add ARP support to WOL")
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Cc: stable@vger.kernel.org
---
 drivers/net/ethernet/cadence/macb_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index f290bc44020e76e681f403306cba998e540a4991..d35bb5f079cd103eea5af7584576c9582a18d22a 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -5915,13 +5915,16 @@ static int __maybe_unused macb_suspend(struct device *dev)
 
 	if (bp->wol & MACB_WOL_ENABLED) {
 		/* Check for IP address in WOL ARP mode */
+		rcu_read_lock();
 		idev = __in_dev_get_rcu(bp->dev);
 		if (idev)
 			ifa = rcu_dereference(idev->ifa_list);
 		if ((bp->wolopts & WAKE_ARP) && !ifa) {
 			netdev_err(netdev, "IP address not assigned as required by WoL walk ARP\n");
+			rcu_read_unlock();
 			return -EOPNOTSUPP;
 		}
+
 		spin_lock_irqsave(&bp->lock, flags);
 
 		/* Disable Tx and Rx engines before  disabling the queues,
@@ -5963,6 +5966,7 @@ static int __maybe_unused macb_suspend(struct device *dev)
 			tmp |= MACB_BFEXT(IP, be32_to_cpu(ifa->ifa_local));
 		}
 		spin_unlock_irqrestore(&bp->lock, flags);
+		rcu_read_unlock();
 
 		/* Change interrupt handler and
 		 * Enable WoL IRQ on queue 0

-- 
2.53.0