The uart_set_options() code unconditionally initalizes the spinlock
on the port. This can cause a deadlock in some situations.
One instance that exposed the problem, was when writing to
/sys/module/kgdboc/parameters/kgdboc to use ttyS0 when the console
is already running on ttyS0. If the spinlock is re-initialized
while the lock is held due to output to the console, there
is a deadlock.
Assume the spinlock is initialized if the port is a console.
Signed-off-by: Randy Witt <rewitt@xxxxxxxxxxxxxxx>
---
drivers/tty/serial/serial_core.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 28cdd28..0a2d277 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1830,9 +1830,13 @@ uart_set_options(struct uart_port *port, struct console *co,
/*
* Ensure that the serial console lock is initialised
* early.
+ * If this port is a console, then the spinlock is already
+ * initialised.
*/
- spin_lock_init(&port->lock);
- lockdep_set_class(&port->lock, &port_lock_key);
+ if (!(uart_console(port) && (port->cons->flags & CON_ENABLED))) {
+ spin_lock_init(&port->lock);
+ lockdep_set_class(&port->lock, &port_lock_key);
+ }
memset(&termios, 0, sizeof(struct ktermios));
--
1.8.3.1
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