net: dsa: mv88e6xxx: fix races between lock and irq freeing

free_irq() waits until all handlers for this IRQ have completed. As the
relevant handler (mv88e6xxx_g1_irq_thread_fn()) takes the chip's reg_lock
it might never return if the thread calling free_irq() holds this lock.

For the same reason kthread_cancel_delayed_work_sync() in the polling case
must not hold this lock.

Also first free the irq (or stop the worker respectively) such that
mv88e6xxx_g1_irq_thread_work() isn't called any more before the irq
mappings are dropped in mv88e6xxx_g1_irq_free_common() to prevent the
worker thread to call handle_nested_irq(0) which results in a NULL-pointer
exception.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -343,6 +343,7 @@ static const struct irq_domain_ops mv88e6xxx_g1_irq_domain_ops = {
 	.xlate	= irq_domain_xlate_twocell,
 };
 
+/* To be called with reg_lock held */
 static void mv88e6xxx_g1_irq_free_common(struct mv88e6xxx_chip *chip)
 {
 	int irq, virq;
@@ -362,9 +363,15 @@ static void mv88e6xxx_g1_irq_free_common(struct mv88e6xxx_chip *chip)
 
 static void mv88e6xxx_g1_irq_free(struct mv88e6xxx_chip *chip)
 {
-	mv88e6xxx_g1_irq_free_common(chip);
-
+	/*
+	 * free_irq must be called without reg_lock taken because the irq
+	 * handler takes this lock, too.
+	 */
 	free_irq(chip->irq, chip);
+
+	mutex_lock(&chip->reg_lock);
+	mv88e6xxx_g1_irq_free_common(chip);
+	mutex_unlock(&chip->reg_lock);
 }
 
 static int mv88e6xxx_g1_irq_setup_common(struct mv88e6xxx_chip *chip)
@@ -469,10 +476,12 @@ static int mv88e6xxx_irq_poll_setup(struct mv88e6xxx_chip *chip)
 
 static void mv88e6xxx_irq_poll_free(struct mv88e6xxx_chip *chip)
 {
-	mv88e6xxx_g1_irq_free_common(chip);
-
 	kthread_cancel_delayed_work_sync(&chip->irq_poll_work);
 	kthread_destroy_worker(chip->kworker);
+
+	mutex_lock(&chip->reg_lock);
+	mv88e6xxx_g1_irq_free_common(chip);
+	mutex_unlock(&chip->reg_lock);
 }
 
 int mv88e6xxx_wait(struct mv88e6xxx_chip *chip, int addr, int reg, u16 mask)
@@ -4506,12 +4515,10 @@ out_g2_irq:
 	if (chip->info->g2_irqs > 0)
 		mv88e6xxx_g2_irq_free(chip);
 out_g1_irq:
-	mutex_lock(&chip->reg_lock);
 	if (chip->irq > 0)
 		mv88e6xxx_g1_irq_free(chip);
 	else
 		mv88e6xxx_irq_poll_free(chip);
-	mutex_unlock(&chip->reg_lock);
 out:
 	if (pdata)
 		dev_put(pdata->netdev);
@@ -4539,12 +4546,10 @@ static void mv88e6xxx_remove(struct mdio_device *mdiodev)
 	if (chip->info->g2_irqs > 0)
 		mv88e6xxx_g2_irq_free(chip);
 
-	mutex_lock(&chip->reg_lock);
 	if (chip->irq > 0)
 		mv88e6xxx_g1_irq_free(chip);
 	else
 		mv88e6xxx_irq_poll_free(chip);
-	mutex_unlock(&chip->reg_lock);
 }
 
 static const struct of_device_id mv88e6xxx_of_match[] = {