Having all the new guards, use them in the 8250 code. This improves
readability, makes error handling easier, and marks locked portions of
code explicit.

serial_unlink_irq_chain() is done separately here because with the
guard() used, those BUG_ON()s can be switched WARN_ON()s as we can
actually handle the conditions and return (despite something went really
wrong).

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
---
 drivers/tty/serial/8250/8250_core.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 82c3636451e5..7d931693b311 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -178,20 +178,22 @@ static void serial_unlink_irq_chain(struct uart_8250_port *up)
 {
 	struct irq_info *i;
 
-	mutex_lock(&hash_mutex);
+	guard(mutex)(&hash_mutex);
 
 	hash_for_each_possible(irq_lists, i, node, up->port.irq)
-		if (i->irq == up->port.irq)
-			break;
+		if (i->irq == up->port.irq) {
+			if (WARN_ON(i->head == NULL))
+				return;
 
-	BUG_ON(i == NULL);
-	BUG_ON(i->head == NULL);
+			if (list_empty(i->head))
+				free_irq(up->port.irq, i);
 
-	if (list_empty(i->head))
-		free_irq(up->port.irq, i);
+			serial_do_unlink(i, up);
+
+			return;
+		}
 
-	serial_do_unlink(i, up);
-	mutex_unlock(&hash_mutex);
+	WARN_ON(1);
 }
 
 /*
-- 
2.50.1