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

[David Nyström]

On Tue, 12 May 2026, 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.

Agreed, Fixes: "i3c: master: Add sysfs option to rescan bus via entdaa"
Is this series headed for 7.1-rc3 ? if not, its probably wise to revert 
the sysfs addition from 7.1-rc

> Frank
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter at intel.com>
>> ---
>>  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
>>
>
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