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

[Adrian Hunter]

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.

> 
>> 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
>>>
>>
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