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

From: Vladimir Oltean <[email-masked]>
Date: Thu, 9 Sep 2021 13:14:51 +0300

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 <[email-masked]>
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: