Re: [PATCH 2/8] i3c: master: Serialize i3c_set_hotjoin() with the maintenance lock

[Adrian Hunter]

On 12/05/2026 19:11, Frank Li wrote:
> On Tue, May 12, 2026 at 03:17:26PM +0300, Adrian Hunter wrote:
>> i3c_set_hotjoin() dispatches the controller's enable_hotjoin() or
>> disable_hotjoin() op and updates master->hotjoin under
>> i3c_bus_normaluse_lock(). That lock is a read-side acquisition of
>> bus->lock (down_read()), so it does not exclude concurrent callers.
>>
>> The hotjoin sysfs attribute can be opened multiple times, and writes
>> through different opens are not serialized.  Two concurrent writers
>> to "hotjoin" can therefore race in i3c_set_hotjoin(), with the
>> controller op and the master->hotjoin store from one call interleaving
>> with the other.  The hardware enable/disable state and the value reported
>> by hotjoin_show() can end up out of sync.
>>
>> Take i3c_bus_maintenance_lock() instead. Toggling Hot Join enable
>> changes bus state and is conceptually a maintenance operation, so the
>> write-side acquisition of bus->lock is the appropriate lock and
>> serializes concurrent callers against each other and against other
>> maintenance operations.
> 
> It should be bug fix, add fix tag here.

Ok

Note, currently it can only go wrong if user space is trying to enable
and disable hotjoin at the same time, which is already broken - user
space itself needs a way to synchronize its hotjoin policy.

> 
> Frank
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>> ---
>>  drivers/i3c/master.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
>> index ab11e2d79aab..38ffc8713167 100644
>> --- a/drivers/i3c/master.c
>> +++ b/drivers/i3c/master.c
>> @@ -649,7 +649,7 @@ static int i3c_set_hotjoin(struct i3c_master_controller *master, bool enable)
>>  			return ret;
>>  	}
>>
>> -	i3c_bus_normaluse_lock(&master->bus);
>> +	i3c_bus_maintenance_lock(&master->bus);
>>
>>  	if (enable)
>>  		ret = master->ops->enable_hotjoin(master);
>> @@ -659,7 +659,7 @@ static int i3c_set_hotjoin(struct i3c_master_controller *master, bool enable)
>>  	if (!ret)
>>  		master->hotjoin = enable;
>>
>> -	i3c_bus_normaluse_unlock(&master->bus);
>> +	i3c_bus_maintenance_unlock(&master->bus);
>>
>>  	if ((enable && ret) || (!enable && !ret) || master->rpm_ibi_allowed)
>>  		i3c_master_rpm_put(master);
>> --
>> 2.51.0
>>