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

[Frank Li]

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.

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
>