Re: [PATCH 0/3] Fix for KSZ DSA switch shutdown

On Thu, Sep 09, 2021 at 11:53:21AM +0200, Lino Sanfilippo wrote:

This patch series fixes a system hang I got each time i tried to shutdown
or reboot a system that uses a KSZ9897 as a DSA switch with a broadcom
GENET network device as the DSA master device. At the time the system hangs
the message "unregister_netdevice: waiting for eth0 to become free. Usage
count = 2." is dumped periodically to the console.

After some investigation I found the reason to be unreleased references to
the master device which are still held by the slave devices at the time the
system is shut down (I have two slave devices in use).

While these references are supposed to be released in ksz_switch_remove()
this function never gets the chance to be called due to the system hang at
the master device deregistration which happens before ksz_switch_remove()
is called.

The fix is to make sure that the master device references are already
released when the device is unregistered. For this reason PATCH1 provides
a new function dsa_tree_shutdown() that can be called by DSA drivers to
untear the DSA switch at shutdown. PATCH2 uses this function in a new
helper function for KSZ switches to properly shutdown the KSZ switch.
PATCH 3 uses the new helper function in the KSZ9477 shutdown handler.

Theses patches have been tested on a Raspberry PI 5.10 kernel with a
KSZ9897. The patches have been adjusted to apply against net-next and are
compile tested with next-next.

Can you try this patch

commit 07b90056cb15ff9877dca0d8f1b6583d1051f724
Author: Vladimir Oltean [off-list ref]
Date:   Tue Jan 12 01:09:43 2021 +0200

    net: dsa: unbind all switches from tree when DSA master unbinds

    Currently the following happens when a DSA master driver unbinds while
    there are DSA switches attached to it: