[PATCH net v3 3/4] net: wan: hdlc: close active devices before protocol detach

[Myeonghun Pak]

Commit ff3516442768 ("WAN: HDLC: Detach protocol before unregistering
device") moved protocol detach ahead of netdev unregister so detach could
still use its state. However, detach_hdlc_protocol() calls
hdlc_setup_dev(), which clears IFF_UP. unregister_netdevice() then sees an
already-down device and skips ndo_stop, leaving an active HDLC device
running while its driver releases resources.

Close the device under RTNL while its protocol is still attached, then
keep the existing detach-before-unregister order. This runs the hardware
stop callback and the protocol close callback before their state is
released.

Audit all current users: c101, n2, pc300too, pci200syn, wanxl,
ixp4xx_hss, fsl_qmc_hdlc and farsync unregister before releasing the
resources used by their close callbacks. The farsync probe unwind can
disable interrupts and free its RX DMA buffer first, but fst_close() does
not use that buffer or require interrupts; the card is also in FST_RESET,
so fst_closeport() does not access the port hardware.

Fixes: ff3516442768 ("WAN: HDLC: Detach protocol before unregistering device")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20260806020541.2011936-2-kuba@xxxxxxxxxx
Co-developed-by: Ijae Kim <ae878000@xxxxxxxxx>
Signed-off-by: Ijae Kim <ae878000@xxxxxxxxx>
Signed-off-by: Myeonghun Pak <mhun512@xxxxxxxxx>
---
 drivers/net/wan/hdlc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/wan/hdlc.c b/drivers/net/wan/hdlc.c
index cbed10b1d862e..a38f90d3006ed 100644
--- a/drivers/net/wan/hdlc.c
+++ b/drivers/net/wan/hdlc.c
@@ -263,6 +263,7 @@ EXPORT_SYMBOL(alloc_hdlcdev);
 void unregister_hdlc_device(struct net_device *dev)
 {
 	rtnl_lock();
+	dev_close(dev);
 	detach_hdlc_protocol(dev);
 	unregister_netdevice(dev);
 	rtnl_unlock();
-- 
2.47.1