media: cec-pin.c: disabling the adapter cannot call kthread_stop

When the adap_enable callback is called the adap->lock is held.
When disabling the adapter it attempts to stop the kthread that
deals with receiving and transmitting messages. However, kthread_stop
waits for the thread to stop, so all that time adap->lock is held.

Unfortunately, the kernel thread itself can call functions that take
that same lock, so a deadlock can occur.

Change the logic to keep the kernel thread running and instead when
disabling the adapter, just set the pin to high, go to idle and then
to state OFF and disable the interrupt. Only stop the kernel thread
when the adapter is deleted.

This way disabling the adapter will not wait for anything and the
deadlock is avoided.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/cec/core/cec-pin.c

@@ -1043,6 +1043,9 @@ static int cec_pin_thread_func(void *_adap)
 					 atomic_read(&pin->work_irq_change) ||
 					 atomic_read(&pin->work_pin_num_events));
 
+		if (kthread_should_stop())
+			break;
+
 		if (pin->work_rx_msg.len) {
 			struct cec_msg *msg = &pin->work_rx_msg;
 
@@ -1090,6 +1093,8 @@ static int cec_pin_thread_func(void *_adap)
 				irq_enabled = false;
 			}
 			cec_pin_high(pin);
+			if (pin->state == CEC_ST_OFF)
+				break;
 			cec_pin_to_idle(pin);
 			hrtimer_start(&pin->timer, ns_to_ktime(0),
 				      HRTIMER_MODE_REL);
@@ -1109,15 +1114,7 @@ static int cec_pin_thread_func(void *_adap)
 		default:
 			break;
 		}
-		if (kthread_should_stop())
-			break;
 	}
-	if (irq_enabled)
-		call_void_pin_op(pin, disable_irq);
-	hrtimer_cancel(&pin->timer);
-	cec_pin_read(pin);
-	cec_pin_to_idle(pin);
-	pin->state = CEC_ST_OFF;
 	return 0;
 }
 
@@ -1134,16 +1131,28 @@ static int cec_pin_adap_enable(struct cec_adapter *adap, bool enable)
 		pin->tx_msg.len = 0;
 		pin->timer_ts = ns_to_ktime(0);
 		atomic_set(&pin->work_irq_change, CEC_PIN_IRQ_UNCHANGED);
+		if (!pin->kthread) {
 			pin->kthread = kthread_run(cec_pin_thread_func, adap,
 						   "cec-pin");
 			if (IS_ERR(pin->kthread)) {
+				int err = PTR_ERR(pin->kthread);
+
 				pr_err("cec-pin: kernel_thread() failed\n");
-			return PTR_ERR(pin->kthread);
+				pin->kthread = NULL;
+				return err;
+			}
 		}
 		hrtimer_start(&pin->timer, ns_to_ktime(0),
 			      HRTIMER_MODE_REL);
-	} else {
-		kthread_stop(pin->kthread);
+	} else if (pin->kthread) {
+		hrtimer_cancel(&pin->timer);
+		cec_pin_high(pin);
+		cec_pin_to_idle(pin);
+		pin->state = CEC_ST_OFF;
+		pin->work_tx_status = 0;
+		atomic_set(&pin->work_pin_num_events, 0);
+		atomic_set(&pin->work_irq_change, CEC_PIN_IRQ_DISABLE);
+		wake_up_interruptible(&pin->kthread_waitq);
 	}
 	return 0;
 }
@@ -1276,7 +1285,10 @@ static void cec_pin_adap_free(struct cec_adapter *adap)
 {
 	struct cec_pin *pin = adap->pin;
 
-	if (pin && pin->ops->free)
+	if (pin->kthread)
+		kthread_stop(pin->kthread);
+	pin->kthread = NULL;
+	if (pin->ops->free)
 		pin->ops->free(adap);
 	adap->pin = NULL;
 	kfree(pin);