Re: [PATCH net] net: bridge: mst: move switchdev call outside rcu

[Nikolay Aleksandrov <razor@blackwall.org>]

On 15/09/2026 13:25, Nikolay Aleksandrov wrote:
> On 15/09/2026 13:23, Paolo Abeni wrote:
>> On 9/11/26 12:50 PM, Nikolay Aleksandrov wrote:
>>> This is a follow-up of one of sashiko's pre-existing bug reports.
>>> br_mst_set_state() calls switchdev_port_attr_set() for nonzero MSTIs
>>> while holding rcu_read_lock() which invokes the blocking switchdev
>>> notifier chain and may sleep. Nonzero MSTI changes come from netlink
>>> with rtnl held. Move the switchdev call before entering the rcu section and
>>> assert that rtnl is held.
>>>
>>> The call cannot be deferred because netlink needs its error and extack.
>>> Also DSA reads the old bridge MST state during the callback and checks it.
>>> A deferred callback will be late and will see the updated state.
>>>
>>> Fixes: 7ae9147f4312 ("net: bridge: mst: Notify switchdev drivers of MST state changes")
>>> Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
>> Clashiko noted that the fixes tag looks inaccurate, should be:
>>
>> Fixes: 3a7c1661ae1383 ("net: bridge: mst: fix vlan use-after-free")
>>
>> do you agree? I can fix the tag while applying the patch no need to repost.
>>
>> /P
>>
> 
> Yeah, I agree. As Ido also noted, that is the correct commit id but it is
> from the same set. :)

err, I meant same release

> Thank you for taking care of this.