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

[David Nyström]

On Wed, 13 May 2026, Adrian Hunter wrote:

> On 12/05/2026 22:42, David Nyström wrote:
>>
>>
>> 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
>
> "i3c: master: Add sysfs option to rescan bus via entdaa" added "do_daa".
> "hotjoin" is a different sysfs attribute.

Replied to wrong patch, correct patch commented now.

>>
>>> 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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>>>
>
>