i2c: designware: Synchronize IRQs when unregistering slave client

Make sure interrupt handler i2c_dw_irq_handler_slave() has finished
before clearing the the dev->slave pointer in i2c_dw_unreg_slave().

There is possibility for a race if i2c_dw_irq_handler_slave() is running
on another CPU while clearing the dev->slave pointer.

Reported-by: Krzysztof Adamski <[email protected]>
Reported-by: Wolfram Sang <[email protected]>
Signed-off-by: Jarkko Nikula <[email protected]>
Signed-off-by: Wolfram Sang <[email protected]>

Author: jhnikula

drivers/i2c/busses/i2c-designware-slave.c

@@ -94,6 +94,7 @@ static int i2c_dw_unreg_slave(struct i2c_client *slave)
 
 	dev->disable_int(dev);
 	dev->disable(dev);
+	synchronize_irq(dev->irq);
 	dev->slave = NULL;
 	pm_runtime_put(dev->dev);